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Around the Internet => Antimustachian Wall of Shame and Comedy => Topic started by: Bob W on June 15, 2015, 10:12:00 AM

Title: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 15, 2015, 10:12:00 AM
Yeah,  I know,  funny huh?

So I checked my tires on the 1999 Mercury Mountaineer.  Damn 32 lbs!   Max inflate rated at 44 lbs.   I filled those babies up to 46 lbs.

Took daughter home to her moms house which is about 45 miles at 32 lbs and MPG 18.5 (I have a digital tracker)   Filled up the air.   Return trip 21.4 MPG.

That is a 15% increase in MPG!  Our annual car gas bill for 2 cars runs about $2,400 (yeah, I know I'm researching higher MPG cars)   So this little trick will save us $400 per year if we do nothing different. 

So yeah,   check your tires and don't be shy about going a tad over the max inflate.    By the way,  hypermilers increase their Prius mileage to 65 mpg simply by overinflating a tad.  Bike riders take note as well --- you could be peddling with 15% less effort. 


YMMV!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: forummm on June 15, 2015, 10:35:07 AM
Filling your tires is great. But you may also have gone uphill on the way there and downhill on the way back. Or driven more efficiently on the way back. The research says any increase should be a few percent or less. Not 15%.

For example:
https://www.fueleconomy.gov/feg/maintain.jsp
http://www.popularmechanics.com/cars/a940/4199963/
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 15, 2015, 10:51:34 AM
The maximum inflation rate only tells you the maximum safe pressure for the tire. The recommended pressure is determined by the manufacturer for optimum performance, and that is what you should follow:

http://blog.tirerack.com/blog/docs-advice-on-tires/what-is-the-best-tire-pressure-for-my-new-tires
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 15, 2015, 10:52:51 AM
You filled your SUV tires to 46lbs?  I bet that thing rides like a buckboard.  And given that it's just a Ford Explorer in a fancy dress, and Ford Explorers are notoriously sensitive to tire failure, I'd say that's a pretty stupid thing to do.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Midwestache on June 15, 2015, 12:26:41 PM
Doesn't over inflation cause a higher likelihood of popping the tire? Also doesn't it decrease the tread unevenly causing you to replace tires earlier? May be a wash in the long run.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: WranglerBowman on June 15, 2015, 12:38:34 PM
Don't over inflate your tires as that can lead to premature tire failure such as tread separation.  Traveling at higher speeds over extended periods of time will cause the tire to heat up and increase the PSI even more, which will likely cause a blow out.  It's not fun when a tire blows at 70 mph and it can cause a lot of damage to your car.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 15, 2015, 12:39:33 PM
You filled your SUV tires to 46lbs?  I bet that thing rides like a buckboard.  And given that it's just a Ford Explorer in a fancy dress, and Ford Explorers are notoriously sensitive to tire failure, I'd say that's a pretty stupid thing to do.

No noticeable difference in ride quality.   

The tires are riding even across contact with the road.   I suppose tire failure is a possibility but I have read a lot of the hypermiler posts on this.   It appears their consensus is that at max inflation or slightly above is oky doky.

Higher inflation pressures usually provide an improvement in steering response and cornering stability while diminishing braking response.  So that is a trade off.   I use my brakes minimally and usually cost up to stop signs and lights.  (I corner and steer way more than brake)

So yeah,  I'll run this little experiment a bit longer.

For those not interested in maxing their MPGs still be sure to check your tires for pressure.   Even a few pounds low can diminish MPG and lead to excess tire wear and possible overheating. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: FrugalSpendthrift on June 15, 2015, 12:57:01 PM
Doesn't over inflation cause a higher likelihood of popping the tire? Also doesn't it decrease the tread unevenly causing you to replace tires earlier? May be a wash in the long run.
I guess they could be more likely to puncture, because they will ride a little stiffer making it tough to absorb potholes.  Over inflated tires are more likely to wear the center prematurely.  They are also more likely to hydroplane in water.

It's all a trade off.  Tires that don't have good traction are good for mpg, because they reduce rolling resistance.  My old subaru came with what I though were terrible tires, until I discovered the tires won awards for low rolling resistance.  They weren't the best for cornering or braking, but they are good for their fleet MPG rating.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Xlar on June 15, 2015, 01:21:00 PM
You filled your SUV tires to 46lbs?  I bet that thing rides like a buckboard.  And given that it's just a Ford Explorer in a fancy dress, and Ford Explorers are notoriously sensitive to tire failure, I'd say that's a pretty stupid thing to do.

No noticeable difference in ride quality.   

The tires are riding even across contact with the road.   I suppose tire failure is a possibility but I have read a lot of the hypermiler posts on this.   It appears their consensus is that at max inflation or slightly above is oky doky.

Higher inflation pressures usually provide an improvement in steering response and cornering stability while diminishing braking response.  So that is a trade off.   I use my brakes minimally and usually cost up to stop signs and lights.  (I corner and steer way more than brake)

So yeah,  I'll run this little experiment a bit longer.

For those not interested in maxing their MPGs still be sure to check your tires for pressure.   Even a few pounds low can diminish MPG and lead to excess tire wear and possible overheating.

Over inflating your tires is definitely dangerous. If by 44 psi max you mean that is the specification in the door jam and you're still under the tire's max rating that is one thing but if you mean that you are over the tire's max rating that is dangerous.

BobW, you have a ton of posts and you're definitely respected within the community so I'd ask you to be very careful when making recommendations that could endanger other readers if they put the recommendation into practice.

I'm also not sure why you put this under the Antimustachian Wall of Shame and Comedy.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Ashyukun on June 15, 2015, 01:24:28 PM
Yeah,  I know,  funny huh?

So I checked my tires on the 1999 Mercury Mountaineer.  Damn 32 lbs!   Max inflate rated at 44 lbs.   I filled those babies up to 46 lbs.

Took daughter home to her moms house which is about 45 miles at 32 lbs and MPG 18.5 (I have a digital tracker)   Filled up the air.   Return trip 21.4 MPG.

That is a 15% increase in MPG!  Our annual car gas bill for 2 cars runs about $2,400 (yeah, I know I'm researching higher MPG cars)   So this little trick will save us $400 per year if we do nothing different. 

So yeah,   check your tires and don't be shy about going a tad over the max inflate.    By the way,  hypermilers increase their Prius mileage to 65 mpg simply by overinflating a tad.  Bike riders take note as well --- you could be peddling with 15% less effort. 


YMMV!

I'm definitely with the others in that inflating the tires to the max rated pressure is courting disaster. If you're not inflating them after driving a LOT in 100-degree weather you're running the risk of them failing when they heat up while driving. That said- inflating them a bit more than the recommended pressure isn't likely to cause a failure, but likely will wear the tires oddly.

On bikes, I'd caution against over-inflating the tires even more strongly- a blowout on a bike is far more likely to hurt you a LOT more than a blowout in a car. However, there is a NOTICEABLE difference in riding when you have the tires properly inflated vs under-inflated, so do keep an eye on the pressure and keep it topped off, it makes the ride a LOT easier.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: MgoSam on June 15, 2015, 01:39:54 PM
Why is this in the anti-mustachian section? Shouldn't this be in the "Share your Badassity!"
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Rollin on June 15, 2015, 02:07:25 PM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.  In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 15, 2015, 02:14:11 PM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.   In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).

No.  Tires offer a suggested range, and an absolute maximum pressure.  Usually the suggested range is something like "32-36 PSI" and the max is something like 44 PSI.  I would recommend you inflate to the 36 in this scenario, not the 44.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 15, 2015, 05:21:29 PM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.  In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).
yep,  I figured this post would bring out the naysayer parrots.   I might sugeest researching the hypermiler tire guys who are experts on this hack.   For the record slight over inflation does not cause uneven wear,  improves cornering,  makes for a stiffer ride,  decreases braking efficiency,  improves traction, decreases braking efficiency and improves mileage significantly.   The hot tire comes from under inflation and the max inflation number already includes anticipation of tire heat up.   You should check your tire inflation when cold.   Of course I could be wrong.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: milesdividendmd on June 15, 2015, 06:07:51 PM
Bob W, I like it!

But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.

Keep us posted either way.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: forummm on June 15, 2015, 06:51:38 PM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.  In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).
yep,  I figured this post would bring out the naysayer parrots.   

(http://i.imgur.com/HW4Yi4B.jpg)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 15, 2015, 07:03:22 PM
That was awesome forummmmm!   
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: TRBeck on June 15, 2015, 07:32:21 PM

But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.


Need more info, please. Instructable or something?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Rollin on June 15, 2015, 08:07:24 PM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.  In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).
yep,  I figured this post would bring out the naysayer parrots.   I might sugeest researching the hypermiler tire guys who are experts on this hack.   For the record slight over inflation does not cause uneven wear,  improves cornering,  makes for a stiffer ride,  decreases braking efficiency,  improves traction, decreases braking efficiency and improves mileage significantly.   The hot tire comes from under inflation and the max inflation number already includes anticipation of tire heat up.   You should check your tire inflation when cold.   Of course I could be wrong.

Yes, as it seems like a lot of misinformation and if you read through they kinda say different things (contradictory).

From USDOT - Understanding Tire Pressure and Load Limits

Tire inflation pressure is the level of air in the tire that provides it with load-carrying capacity and affects the overall performance of the vehicle. The tire inflation pressure is a number that indicates the amount of air pressure– measured in pounds per square inch (psi)–a tire requires to be properly inflated. (You will also find this number on the vehicle information placard expressed in kilopascals (kPa), which is the metric measure used internationally.)

Manufacturers of passenger vehicles and light trucks determine this number based on the vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size.The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure." (As you will read below, it is difficult to obtain the recommended tire pressure if your tires are not cold.)

Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.


Or just look at some of the tables in the link below and see how load capacity increases with tire pressure, so if I add 7 passengers to my van I add probably 900-1200 extra pounds and should increase my pressure to accommodate that - up to the maximum of course.  Believe me when I say i can feel the difference when I am at the lower recommended inflation pressure of 32 psi and have my van full of buddies and their camping gear and mountain bikes, and when I'm up near the high end of the inflation max.


http://toyotires.com/sites/default/files/page-files/LoadInflation_Table_P-LT_102913.pdf
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: milesdividendmd on June 15, 2015, 09:38:44 PM


But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.


Need more info, please. Instructable or something?

This captures the essence of the pursuit.

http://www.varasanos.com/pizzarecipe.htm

Or if you want the specifics of my personal quest I wrote a post about it on my eponymous blog entitled "penny wise and pound foolish."
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: RWD on June 15, 2015, 09:51:56 PM
You filled your SUV tires to 46lbs?  I bet that thing rides like a buckboard.  And given that it's just a Ford Explorer in a fancy dress, and Ford Explorers are notoriously sensitive to tire failure, I'd say that's a pretty stupid thing to do.

The tires are riding even across contact with the road.

To verify an even contact patch you'll need to measure tread depth at three points (inside, middle, outside) after putting on some significant mileage. Definitely something to keep an eye on.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Xlar on June 16, 2015, 07:11:38 AM
It has always been my practice to inflate to recommended tire pressures when I am not hauling a heavy load of people or cargo.  So, when I am loaded up I pressure up.  The maximum load rating for a tire is based on the higher pressure.  In other words you should increase the tire pressure as your load is increased.  How can having higher pressure (to the load rating) with a light load of people or cargo cause a blowout problem other than some premature wear down the center?

For those that suggest the tire getting hotter under higher pressure, therefore increasing the chances of a blowout, I'm not sure you have this correct.  Now, if the tires are underinflated you can have significant issues with heat causing blowouts.  Remember all the Explorer tire blowouts with Firestone years ago?  Much of that was underinflation, increased heat, coupled with significant steering movement at high speeds (avoiding an obstacle for example).
yep,  I figured this post would bring out the naysayer parrots.   I might sugeest researching the hypermiler tire guys who are experts on this hack.   For the record slight over inflation does not cause uneven wear,  improves cornering,  makes for a stiffer ride,  decreases braking efficiency,  improves traction, decreases braking efficiency and improves mileage significantly.   The hot tire comes from under inflation and the max inflation number already includes anticipation of tire heat up.   You should check your tire inflation when cold.   Of course I could be wrong.

Yes, as it seems like a lot of misinformation and if you read through they kinda say different things (contradictory).

From USDOT - Understanding Tire Pressure and Load Limits

Tire inflation pressure is the level of air in the tire that provides it with load-carrying capacity and affects the overall performance of the vehicle. The tire inflation pressure is a number that indicates the amount of air pressure– measured in pounds per square inch (psi)–a tire requires to be properly inflated. (You will also find this number on the vehicle information placard expressed in kilopascals (kPa), which is the metric measure used internationally.)

Manufacturers of passenger vehicles and light trucks determine this number based on the vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size.The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure." (As you will read below, it is difficult to obtain the recommended tire pressure if your tires are not cold.)

Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.


Or just look at some of the tables in the link below and see how load capacity increases with tire pressure, so if I add 7 passengers to my van I add probably 900-1200 extra pounds and should increase my pressure to accommodate that - up to the maximum of course.  Believe me when I say i can feel the difference when I am at the lower recommended inflation pressure of 32 psi and have my van full of buddies and their camping gear and mountain bikes, and when I'm up near the high end of the inflation max.


http://toyotires.com/sites/default/files/page-files/LoadInflation_Table_P-LT_102913.pdf

I agree that you need to increase the pressure in the tire when you add more load. I even would agree that increasing the pressure would improve fuel economy and all the rest of it. The bit that I disagree about and that is dangerous is inflating the tire over the maximum tire pressure listed on the tire. The manufacture chose that pressure to be the maximum because, from their testing, it was the maximum safe pressure that the tire could be filled before failing...

I don't see how there could be any disagreement that this is dangerous. Now if Bob W had said that he inflated up to the maximum tire pressure then I would be totally okay with that and agree that it would improve fuel economy while reducing braking performance.

Also, as a note, all tire pressures should be measured when the tire is cold (not after driving on your tires). So Bob W is correct in saying that the listed maximum pressure takes into account that the tire will heat up during regular driving.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: forummm on June 16, 2015, 07:17:35 AM


But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.


Need more info, please. Instructable or something?

This captures the essence of the pursuit.

http://www.varasanos.com/pizzarecipe.htm

Or if you want the specifics of my personal quest I wrote a post about it on my eponymous blog entitled "penny wise and pound foolish."

I've met Varasano a couple times. He even offered me pizza during the middle of a 10k I was running as I passed by his restaurant (I declined). True story. They have Rubik's cubes at some of the tables.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: TheGrimSqueaker on June 16, 2015, 07:59:51 AM
I recently bought tires for the Squeakmobile (Scion). To maximize my benefit, and because the factory tires had turned out to be such crap that they wore out long before their estimated mileage, I decided to get some more expensive tires that came with a mileage warranty. If the tires fail or wear out before the warranty period expires, the manufacturer will either replace the tire, or amortize the cost of the remaining mileage and give that to me as a credit toward the replacement tire. This worked out to a better cost per actual mile than if I did a like-for-like replacement.

Does over-inflating the tires affect the warranty coverage? I like the idea of extra mileage, but do have to go over potholes and rough terrain sometimes (while camping or hiking). It makes sense for me to consider other costs.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Rollin on June 16, 2015, 08:20:24 AM
I agree that you need to increase the pressure in the tire when you add more load. I even would agree that increasing the pressure would improve fuel economy and all the rest of it. The bit that I disagree about and that is dangerous is inflating the tire over the maximum tire pressure listed on the tire. The manufacture chose that pressure to be the maximum because, from their testing, it was the maximum safe pressure that the tire could be filled before failing...

I don't see how there could be any disagreement that this is dangerous. Now if Bob W had said that he inflated up to the maximum tire pressure then I would be totally okay with that and agree that it would improve fuel economy while reducing braking performance.

Also, as a note, all tire pressures should be measured when the tire is cold (not after driving on your tires). So Bob W is correct in saying that the listed maximum pressure takes into account that the tire will heat up during regular driving.

Correct, correct!  Everything that I have read says DO NOT inflate about the maximum.  I think there was some confusion in earlier posts when they used the term "over-inflate" when they actually meant to write "inflate above the recommended psi" - not the max psi.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Mr. Green on June 16, 2015, 09:20:50 AM
No on here has asked the question why slightly over-inflating those tires would increase gas mileage. It is most certainly because you have created a more "rounded" contact surface. Less surface contact equals less friction to cause rolling resistance. I would simply caution you that less surface contact also equals poorer handling.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Xlar on June 16, 2015, 09:24:08 AM
I agree that you need to increase the pressure in the tire when you add more load. I even would agree that increasing the pressure would improve fuel economy and all the rest of it. The bit that I disagree about and that is dangerous is inflating the tire over the maximum tire pressure listed on the tire. The manufacture chose that pressure to be the maximum because, from their testing, it was the maximum safe pressure that the tire could be filled before failing...

I don't see how there could be any disagreement that this is dangerous. Now if Bob W had said that he inflated up to the maximum tire pressure then I would be totally okay with that and agree that it would improve fuel economy while reducing braking performance.

Also, as a note, all tire pressures should be measured when the tire is cold (not after driving on your tires). So Bob W is correct in saying that the listed maximum pressure takes into account that the tire will heat up during regular driving.

Correct, correct!  Everything that I have read says DO NOT inflate about the maximum.  I think there was some confusion in earlier posts when they used the term "over-inflate" when they actually meant to write "inflate above the recommended psi" - not the max psi.

Glad we're on the same page :)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 16, 2015, 09:46:20 AM
So after much consideration of everyone's input I am backing off from 46 to 44 lbs.   That should hopefully end the debate on the over(hyper) inflation question.   My braking distance will remain relatively high,  my cornering will remain improved,  my mpg will be substantially increased,  my ride somewhat rougher (I have not noticed this at all) and I should be within safety specs.   Regarding the tires wearing more in the middle, this is old school pre radial talk.

I don't think there is a perfect inflation number for all the variables and I may be on the high side.  But my vehicle does weigh 4,000 pounds.  Since I will be buying a high MPG car in the not too distant future this will be my temporary behavior for this vehicle.   

From my understanding of it, hysteresis plays the biggest role in tire fatigue. This seems to be demonstrated by the fact that tires which have been run at low pressure for extended periods of time are prone to cord failure and tread separation. So reducing sidewall hysteresis by means of increased pressure would appear like a good way to reduce the occurrence of fatigue failure.

It would also suggest that a tire inflated towards the higher end of its Max inflation stamp will last longer than one inflated below the suggested rates.   

It is a very interesting discussion over at eccomodder.com regarding this topic.  Considering a tire may make 30 million rotations in its useable life, that is a lot of freaking rotations!

Appreciate everyone's cautioning about safety --- safety first!   I am taking that into consideration. 

I am saving my pennies and looking towards a 5-10K fuel efficient vehicle and retiring the gas hog to back up,  camping and snow duty.   It is a great SUV but at 300K it is time to consider options. 

Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: r3dt4rget on June 16, 2015, 09:52:01 AM
No on here has asked the question why slightly over-inflating those tires would increase gas mileage. It is most certainly because you have created a more "rounded" contact surface. Less surface contact equals less friction to cause rolling resistance. I would simply caution you that less surface contact also equals poorer handling.
That's not correct. Modern tire's are designed with metal ribs that force a tire to hold it's shape within reasonable pressure ranges. So the shape of the tire between 30 PSI and 50 PSI is not really changed when it's under the weight of the vehicle. It is a myth that higher pressure = more tire wear. This myth originates from pre-radial tire design, when indeed tires would be shaped like donuts.

It's more efficient because less energy is lost. Have you ever tried to ride a bike with a flat tire? A lot of energy is wasted trying to get force to the ground through a flat tire.

I have a lot of personal experience with this subject. On my last set of tires I ran them at about 50 PSI. Max rating was 44 PSI. Tread warranty on those tires was 80,000 miles. With regular balancing, alignments, and checking the pressure, I made them last the full warranty period before replacement. In my own data I discovered a 7% increase in fuel economy going from 30 PSI to 40 PSI.

What people have to realize is that the "Max Pressure" is not the true maximum pressure. There is a large safety margin put in place by the manufacturer. Risk management departments would never allow a manufacturer to state the actual maximum performance of a product. If you visit hypermiler forums you will encounter people who inflate their tires to 50, even 65 PSI without a single issue, despite the max ratings being 44 or 51 PSI. The tires can handle much more than their stated maximum, especially when these tires are for light commuter cars not driving under extreme circumstances.

Also realize that the tire pressure information for your car is calculated for maximum ride comfort, not efficiency or performance. A car with tires inflated to 30 PSI will ride more comfortably than an identical car with tires inflated to 45 PSI, without costing the car maker any money in suspension design. The reality is that a car will handle, stop, accelerate, and get better economy at higher tire pressures while sacrificing some ride and noise comfort.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 16, 2015, 09:54:46 AM
No on here has asked the question why slightly over-inflating those tires would increase gas mileage. It is most certainly because you have created a more "rounded" contact surface. Less surface contact equals less friction to cause rolling resistance. I would simply caution you that less surface contact also equals poorer handling.

Yeah,  it doesn't actually work like that with radials.   A slight over inflation does not cause a rounding from side to side. (a hump in the middle of the tread)  The rolling resistance is diminished as the tire is rounder and there is less contact from front to back on the tire.  The tire does not hump in the middle of the tread as has been suggested.   (to test your tires for even wear simply use a paint roller and paint the tire tread.  Let dry and then drive for a bit.   You will be able to see the wear patterns pretty quickly)

As far as handling,  autocrossers (those who play parking lot swerve and steer time trial contests) overinflate as a rule.   The over inflation improves cornering significantly.    Over inflation does effect braking distance by increasing it.   
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: milesdividendmd on June 16, 2015, 09:59:19 AM



But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.


Need more info, please. Instructable or something?

This captures the essence of the pursuit.

http://www.varasanos.com/pizzarecipe.htm

Or if you want the specifics of my personal quest I wrote a post about it on my eponymous blog entitled "penny wise and pound foolish."

I've met Varasano a couple times. He even offered me pizza during the middle of a 10k I was running as I passed by his restaurant (I declined). True story. They have Rubik's cubes at some of the tables.

You must be an atlantite.

How's the pie?!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 16, 2015, 10:03:24 AM
No on here has asked the question why slightly over-inflating those tires would increase gas mileage. It is most certainly because you have created a more "rounded" contact surface. Less surface contact equals less friction to cause rolling resistance. I would simply caution you that less surface contact also equals poorer handling.
That's not correct. Modern tire's are designed with metal ribs that force a tire to hold it's shape within reasonable pressure ranges. So the shape of the tire between 30 PSI and 50 PSI is not really changed when it's under the weight of the vehicle. It is a myth that higher pressure = more tire wear. This myth originates from pre-radial tire design, when indeed tires would be shaped like donuts.

It's more efficient because less energy is lost. Have you ever tried to ride a bike with a flat tire? A lot of energy is wasted trying to get force to the ground through a flat tire.

I have a lot of personal experience with this subject. On my last set of tires I ran them at about 50 PSI. Max rating was 44 PSI. Tread warranty on those tires was 80,000 miles. With regular balancing, alignments, and checking the pressure, I made them last the full warranty period before replacement. In my own data I discovered a 7% increase in fuel economy going from 30 PSI to 40 PSI.

What people have to realize is that the "Max Pressure" is not the true maximum pressure. There is a large safety margin put in place by the manufacturer. Risk management departments would never allow a manufacturer to state the actual maximum performance of a product. If you visit hypermiler forums you will encounter people who inflate their tires to 50, even 65 PSI without a single issue, despite the max ratings being 44 or 51 PSI. The tires can handle much more than their stated maximum, especially when these tires are for light commuter cars not driving under extreme circumstances.

Also realize that the tire pressure information for your car is calculated for maximum ride comfort, not efficiency or performance. A car with tires inflated to 30 PSI will ride more comfortably than an identical car with tires inflated to 45 PSI, without costing the car maker any money in suspension design. The reality is that a car will handle, stop, accelerate, and get better economy at higher tire pressures while sacrificing some ride and noise comfort.

Yes,  glad to see you did an 80K test.   You are spot on with the exception of the "stop" part.  Everything I've read from hypermilers and autocrossers suggests that stopping is diminished.   

Thanks for you input!!!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Rollin on June 16, 2015, 10:14:50 AM
No on here has asked the question why slightly over-inflating those tires would increase gas mileage. It is most certainly because you have created a more "rounded" contact surface. Less surface contact equals less friction to cause rolling resistance. I would simply caution you that less surface contact also equals poorer handling.
That's not correct. Modern tire's are designed with metal ribs that force a tire to hold it's shape within reasonable pressure ranges. So the shape of the tire between 30 PSI and 50 PSI is not really changed when it's under the weight of the vehicle. It is a myth that higher pressure = more tire wear. This myth originates from pre-radial tire design, when indeed tires would be shaped like donuts.

It's more efficient because less energy is lost. Have you ever tried to ride a bike with a flat tire? A lot of energy is wasted trying to get force to the ground through a flat tire.

I have a lot of personal experience with this subject. On my last set of tires I ran them at about 50 PSI. Max rating was 44 PSI. Tread warranty on those tires was 80,000 miles. With regular balancing, alignments, and checking the pressure, I made them last the full warranty period before replacement. In my own data I discovered a 7% increase in fuel economy going from 30 PSI to 40 PSI.

What people have to realize is that the "Max Pressure" is not the true maximum pressure. There is a large safety margin put in place by the manufacturer. Risk management departments would never allow a manufacturer to state the actual maximum performance of a product. If you visit hypermiler forums you will encounter people who inflate their tires to 50, even 65 PSI without a single issue, despite the max ratings being 44 or 51 PSI. The tires can handle much more than their stated maximum, especially when these tires are for light commuter cars not driving under extreme circumstances.

Also realize that the tire pressure information for your car is calculated for maximum ride comfort, not efficiency or performance. A car with tires inflated to 30 PSI will ride more comfortably than an identical car with tires inflated to 45 PSI, without costing the car maker any money in suspension design. The reality is that a car will handle, stop, accelerate, and get better economy at higher tire pressures while sacrificing some ride and noise comfort.

...and you are still alive to type this out!?  My gawd, you live on the edge :)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Posthumane on June 16, 2015, 10:38:49 AM
I would like to point out that the max inflation pressure on a tire sidewall has a fair amount of safety margin built into it. Tires are often inflated above the rated max inflation pressure in order to seat the bead on the rim when it is being installed. Modern car tires in good shape won't catastrophically fail from over inflation until about 120 psi. That being said, when one does go it is indeed very spectacular and dangerous. I'm sure you can find a mechanic training video on youtube which shows a tire being shot 100 m in the air as it explodes, and taking out the dummy standing over it.

There are optimal pressure calculators for bicycle tires which will specify the inflation pressure for minimal rolling resistance given the tire size and load place on it. Going either above or below that will increase resistance. For me with a slightly loaded bike the optimal inflation pressure is around 90 psi on 700c-28 tires. Some tire brands will let me reach that pressure, some won't (my current ones have a max rating of 85 psi so that's what I run them at).

For autocrossing tires are typically inflated to get optimal cornering grip, not lowest rolling resistance. At low pressures the tire will roll over onto the sidewall slightly under hard cornering, reducing contact patch and grip. This can be checked by putting white shoe polish or on your sidewalls and running a course, then adjusting the pressure and repeating. A more accurate way is to measure tire temperatures at various points on the tire with an IR thermometer. However, pressures for optimal rolling resistance tend to be much higher than for optimal cornering.

Although radial tires don't really balloon as much as old bias ply ones did, they don't hold their shape perfectly and you may still find slightly increased wear in the centre of the tread compared to the sides. Conversely, under inflated tires will wear more on the edges of the tread. It's up to you to determine if this tradeoff is worth the decreased fuel consumption.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 16, 2015, 01:42:34 PM
Yeah,  I'm doing the paint the tire trick to assure myself of the wear pattern.  I'll report back on the outcome. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: JAYSLOL on June 16, 2015, 07:35:04 PM
I run my work truck and my car tires slightly over-inflated, but only by 2-4 lbs.  I think its good to keep in mind is that tire size makes a difference.  On a small car (example my tercel) the standard rims can use anywhere from 155 - 185 wide tires (although at one point i had an un-mustachian set of much wider fancy alloy rims and low profile tires on it, face palm).   The 185s take 10+% off the fuel economy and cost more to buy compared to the 155s.  I've found it has been better having a small car and running narrower tires only slightly over inflated to still get full life out of a very inexpensive set of rubber rather than having a large vehicle that requires large tires and over inflating the shit out of them to get back some of the mileage
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: forummm on June 16, 2015, 07:56:11 PM



But then I'm the type of guy who alters his oven to reach 850 F in order to cook a proper pizza.


Need more info, please. Instructable or something?

This captures the essence of the pursuit.

http://www.varasanos.com/pizzarecipe.htm

Or if you want the specifics of my personal quest I wrote a post about it on my eponymous blog entitled "penny wise and pound foolish."

I've met Varasano a couple times. He even offered me pizza during the middle of a 10k I was running as I passed by his restaurant (I declined). True story. They have Rubik's cubes at some of the tables.

You must be an atlantite.

How's the pie?!

It's been a few years since I've been over there, but I remember it being very good.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: GetItRight on June 17, 2015, 10:50:29 AM
Enjoy the reduction in traction and accelerated tire wear, and beware blowouts. Ideal tire pressure depends on the tire, wheel, vehicle weight, and weight distribution. Increase tire pressure if loaded heavy. By running the tire pressure you mentioned in the original post you are creating a safety hazard for yourself and others on the road, and depending on how much more quickly you wear out your tires maybe not even saving money.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: gimp on June 17, 2015, 11:02:21 AM
Bob, I respect you, but this is some seriously stupid fucking shit. Come on. You've inflated tires beyond their maximum inflate rating, which is itself far beyond what your vehicle's manufacturer recommends.

They don't recommend this so that you burn more gas. They recommend this for safety, tire longevity, and oh yeah, have I mentioned safety? Tire blowouts, reduced traction, uneven tire wear (see: tire blowouts) all sorts of dumb shit happens when you do this.

Any mechanic out there will tell you that what you are doing is dangerous as well as stupid.

Congratulations on maybe saving $400 a year. Tires are expensive and treating them this way will result in you paying for new tires. The less you spend on your tires, by the way, the more likely they are to fail from being abused like this.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 17, 2015, 12:45:53 PM
Bob, I respect you, but this is some seriously stupid fucking shit. Come on. You've inflated tires beyond their maximum inflate rating, which is itself far beyond what your vehicle's manufacturer recommends.
I take it you didn't read the whole thread?

Running the tires at sidewall maximum pressure seems perfectly safe - I've done it for years with no problems, as have whole communities of people online. Even 2 psi above sidewall maximum is probably fine, given that the sidewall maximum 44psi in the morning increases significantly as the tire heats up - but he backed down to the 44psi recommended by the tire manufacturer as soon as it was suggested in the thread.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: frugalnacho on June 17, 2015, 01:07:32 PM
Why is this in the anti-mustachian section? Shouldn't this be in the "Share your Badassity!"

Or an ad on the weather channel?  One weird trick to increase gas mileage by 15%!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 17, 2015, 01:32:13 PM
Why is this in the anti-mustachian section? Shouldn't this be in the "Share your Badassity!"

Or an ad on the weather channel?  One weird trick to increase gas mileage by 15%!

No idea?  I thought I started the thread in either GD or SYB?  Perhaps a moderator attempt at humor?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 17, 2015, 01:45:15 PM
Bob, I respect you, but this is some seriously stupid fucking shit. Come on. You've inflated tires beyond their maximum inflate rating, which is itself far beyond what your vehicle's manufacturer recommends.
I take it you didn't read the whole thread?

Running the tires at sidewall maximum pressure seems perfectly safe - I've done it for years with no problems, as have whole communities of people online. Even 2 psi above sidewall maximum is probably fine, given that the sidewall maximum 44psi in the morning increases significantly as the tire heats up - but he backed down to the 44psi recommended by the tire manufacturer as soon as it was suggested in the thread.

Well I have backed it down to 44 for now.  (doubt most people read 100 comment long threads in entirety.)

A couple of additional comments for those starting at the bottom of the thread. ---- Most of the comments saying it is o.k. to run em high seem to be well researched/reasoned and to have actually done this on a regular basis.   Many of the "you're gonna die at 45 psi" folks appear to be shooting from the hip.    The reality is that there are pluses and minuses and risks on both ends of the equation.   And I do really appreciate the "don't do nuthin stupid" input.   

I have a propensity to do stupid things on a pretty regular basis, so it is nice when someone mentions that I may be entering that territory.  (yeah, I did the math and this isn't the stupid thing territory)

That and most failed to notice that I am driving a 4,000 lb SUV that goes close to 5,000 lbs when I'm full up with people.   That in itself fits the definition of heavy load which is what the max inflation number is designed for. 

Been too rainy here (like nonstop) to do the paint test for even wear.  I'll be sure to update this thread once that test is done, even if it is off the screen by then.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Gone Fishing on June 17, 2015, 02:01:28 PM
Enjoying the thread! Looking foward to seeing the results of the paint test.  I have routinely inflated my tires up to the manufacturer's limit for better milage.  I never done any real milage testing, but my tires have never worn abnormally either.  I do notice a little more vibration at 70+MPH, but a mustachian/hypermiler shouldn't really be driving over 70 anyway.

Slowing down on the hwy gives me the best milage, 55 is around 15% better than 70, but can irritate other drivers and cause a hazard if too much slower than the flow of traffic. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: MoneyCat on June 17, 2015, 05:30:06 PM
Got to say I love the title of this thread.  Somebody has been reading Buzzfeed! :-P
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 17, 2015, 08:41:50 PM
Enjoying the thread! Looking foward to seeing the results of the paint test.  I have routinely inflated my tires up to the manufacturer's limit for better milage.  I never done any real milage testing, but my tires have never worn abnormally either.  I do notice a little more vibration at 70+MPH, but a mustachian/hypermiler shouldn't really be driving over 70 anyway.

Slowing down on the hwy gives me the best milage, 55 is around 15% better than 70, but can irritate other drivers and cause a hazard if too much slower than the flow of traffic.
since my vehicle is a gas hog and has a fuel economy read out I like to drive 55 while I do the time vs mpg equation in my head.   Drives my wife freaking crazy.       
Title: .
Post by: This_Is_My_Username on June 18, 2015, 06:24:37 AM
i also use very high psi (~45), and the only down side is that the traction is very poor cornering in the wet.

I have had a few short moments where the car loses traction and drifts sidewards.  A reminder to drive slower : )

otherwise, its all good, there are big savings to be had : )
Title: Re: .
Post by: Bob W on June 18, 2015, 06:45:44 AM
i also use very high psi (~45), and the only down side is that the traction is very poor cornering in the wet.

I have had a few short moments where the car loses traction and drifts sidewards.  A reminder to drive slower : )

otherwise, its all good, there are big savings to be had : )
yeah since I generally follow hypermiler methods I do sometimes corner a little hard to avoid braking.   I'll have to watch that.  It would seem that a stiffer tire may be more prone to slippage on wet pavement,  although according to auto crossers it significantly improves cornering on dry.    Driving slow with high awareness is always a good policy. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 07:01:57 AM
Also if the tires are to inflated, if you hit a bad pothole the tire could blowout.  You would then be out a tire.
personal experience or a reference source?  I'm kinda doubting manufacturers would approve inflation rates that lead to blow outs but as always I could be wrong.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 18, 2015, 07:09:05 AM
That and most failed to notice that I am driving a 4,000 lb SUV that goes close to 5,000 lbs when I'm full up with people.   That in itself fits the definition of heavy load which is what the max inflation number is designed for.

The people that designed and built your vehicle know exactly what it weighs and have done extensive testing to determine the optimum pressure. They also know that people will often carry passengers in the vehicle. The fact that you chose the number on the tire and not what the manufacturer of your vehicle recommends indicates that you made an uneducated choice.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 07:40:12 AM
That and most failed to notice that I am driving a 4,000 lb SUV that goes close to 5,000 lbs when I'm full up with people.   That in itself fits the definition of heavy load which is what the max inflation number is designed for.

The people that designed and built your vehicle know exactly what it weighs and have done extensive testing to determine the optimum pressure. They also know that people will often carry passengers in the vehicle. The fact that you chose the number on the tire and not what the manufacturer of your vehicle recommends indicates that you made an uneducated choice.

And again, the max SUGGESTED pressure is likely in the 36-38PSI range (there will be a "suggested range" of ~32-38PSI on the door jam) and THIS is what Ford suggests as a Max.  The 44 or 46PSI is not a "suggested" max, it's a "DO NOT UNDER ANY CIRCUMSTANCES GO OVER THIS LEVEL" max.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 09:28:17 AM
Interesting. So you think that Ford knows better about the behavior of all of the tires that could conceivably be put on a Ford than the manufacturer of any given tire knows about its product?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Posthumane on June 18, 2015, 09:45:34 AM
There are a number of variables that go into deciding what pressure to put on the door jamb. Door jamb labels are based on the stock tire make/model/size and take into account things like noise/vibration/harshness (NVH) which results from higher inflation pressures, as well as tire wear based on common load patters. If you routinely load the vehicle to max or run a slightly narrower than stock tire, higher inflation pressures are a must.

Basically, inflation pressure is a trade off of several factors. Higher pressures result in less compliance which generally results in lower rolling resistance, to a point. A certain amount of compliance is necessary though since having the entire wheel move vertically as a result of minute surface undulations results in higher rolling resistance. A high pressure generally won't result in a reduction in wet traction unless you get to the point where contact patch starts to be significantly reduced. In fact, hydroplaning resistance is directly proportional to tire pressure in smooth tires (i.e. not designed specifically with water channels). However, with less sidewall compliance, going past the traction limit will result in a much more sudden loss of grip with less warning compared to tires with lower pressure, which for many drivers may result in poorer performance at the limit.

The paint on the tire trick probably won't tell you much about predicted tire wear across the tread. It only shows gross differences where there is or isn't pavement contact. The entire tread area should still be touching the ground with increased pressure (if it isn't, then you're waaay over inflated) but there will be a pressure gradient across the tread - the centre will have slightly higher ground pressure than the sides. Your paint will still wear off fairly evenly on the tread.

Btw, an under inflated tire is much more likely to cause a blowout than an over inflated one. Several causes of blowouts include overheating of the tires from too much sidewall flex, the tire bead rolling off the rim during cornering, and the tire bottoming out on the rim when hitting something like a pothole.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 10:05:35 AM
Interesting. So you think that Ford knows better about the behavior of all of the tires that could conceivably be put on a Ford than the manufacturer of any given tire knows about its product?

I don't think either one of them would suggest inflating to or more than the stated maximum, so it really doesn't matter now, does it?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: GuitarStv on June 18, 2015, 10:38:31 AM
My understanding of bike tire pressure is that higher doesn't equal better.  You want to aim for about 15% deflection of the tire when the rider's weight goes on it.  (You can find charts online for given tires and rider weight).  Higher tire pressures than that actually make you slower because the bike tire wastes more energy bumping up and down along uneven road surfaces.  Your tire is also your suspension on your bike, very high pressures will be painful on your hands and hard on your rims.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 18, 2015, 10:57:58 AM
Interesting. So you think that Ford knows better about the behavior of all of the tires that could conceivably be put on a Ford than the manufacturer of any given tire knows about its product?

Yes.  All the tire manufacturers are in agreement...use the pressure recommended by the maker of the vehicle. The information is readily available to anyone who bothered to look it up instead of guessing:

Firestone states this on their website:

"The first place to look for the correct air pressure for your specific tires is your vehicle owner’s manual. Correct air pressure should also be listed on the tire placard attached to the vehicle door edge, doorpost, glove box door or fuel door."

Bridgestone:

"Look on the driver’s side door jamb or your owner’s manual to find the recommended cold tire PSI for your front and rear tires.  If you cannot find it, you should consult your vehicle dealer, manufacturer, or a qualified tire professional."

Goodyear:

"To find the proper air pressure for your tires, look in your vehicle's owner's manual, on the sticker on the driver's side doorjamb, or in the glove box."
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 11:04:12 AM
Posthumane thank you for you thoughtful and obviously educated thoughts.    So I should just skip the paint test and it wouldn't tell me more than a visual inspection regarding the bell shaped pressure gradient differential you describe.

On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

Tire wear is important to me as tires in this size vehicle (well any really) are expensive. 

Here is a quote from over at one of the hypermiler sites "Higher air pressure tires run cooler. This is the main reason for less wear. Less friction less wear,"   I fell pretty confident that is true.    So by maxing out my inflation (and not an ounce over mind you)  I should be saving on both gas and tires.  Sweeeeet!

I'm comfortable with the supposed bumpier ride attributed to higher pressured tires.   It appears I do most of my driving on very smooth roads. 

Anyone reading this please check your tires to be sure you are above minimum inflation as that can cause overheating in summer weather like we're having. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 11:10:52 AM
Interesting. So you think that Ford knows better about the behavior of all of the tires that could conceivably be put on a Ford than the manufacturer of any given tire knows about its product?

Yes.  All the tire manufacturers are in agreement...use the pressure recommended by the maker of the vehicle. The information is readily available to anyone who bothered to look it up instead of guessing:

Firestone states this on their website:

"The first place to look for the correct air pressure for your specific tires is your vehicle owner’s manual. Correct air pressure should also be listed on the tire placard attached to the vehicle door edge, doorpost, glove box door or fuel door."

Bridgestone:

"Look on the driver’s side door jamb or your owner’s manual to find the recommended cold tire PSI for your front and rear tires.  If you cannot find it, you should consult your vehicle dealer, manufacturer, or a qualified tire professional."

Goodyear:

"To find the proper air pressure for your tires, look in your vehicle's owner's manual, on the sticker on the driver's side doorjamb, or in the glove box."

One suspects that is a recommendation with the focus on comfort and not fuel economy or tire life.   Mustachians tend to not follow the herd and be less concerned with comfort and more concerned with economy.   One would guess that companies such as GM are not very good at predicting risk or budgeting given their poor record of financial management.    So yeah,  I didn't even go to their sites and focused my research on sites with people actually hyperinflating tires with years of experience.    You could check out eccomoder.com
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 18, 2015, 11:22:47 AM
On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

AWD does nothing to make tires wear unevenly. Perhaps you should talk to a mechanic instead of a friend.

The X pattern for rotation is fine, unless you have directional tires. Directional tires should only be switched from to rear and would be turning the "wrong" way if put on the other side of the vehicle.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 11:25:18 AM
One suspects that is a recommendation with the focus on comfort and not fuel economy or tire life.   Mustachians tend to not follow the herd and be less concerned with comfort and more concerned with economy.   One would guess that companies such as GM are not very good at predicting risk or budgeting given their poor record of financial management.    So yeah,  I didn't even go to their sites and focused my research on sites with people actually hyperinflating tires with years of experience.    You could check out eccomoder.com

Seriously?  Car companies fall all over themselves for a fraction of a MPG, and you think they're sandbagging for a little ride comfort?  You want to disregard the engineers who do this stuff for a living and listen to Joe Schmo on the internet, fine, but don't tell us it's anything resembling a good idea. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 18, 2015, 11:29:30 AM
One suspects that is a recommendation with the focus on comfort and not fuel economy or tire life.   Mustachians tend to not follow the herd and be less concerned with comfort and more concerned with economy.   One would guess that companies such as GM are not very good at predicting risk or budgeting given their poor record of financial management.    So yeah,  I didn't even go to their sites and focused my research on sites with people actually hyperinflating tires with years of experience.    You could check out eccomoder.com

No thanks. I'm sure the technicians at the auto manufacturers know what they're talking about, and also the tire manufacturers who state the very same thing.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 11:32:27 AM
Interesting. So you think that Ford knows better about the behavior of all of the tires that could conceivably be put on a Ford than the manufacturer of any given tire knows about its product?

I don't think either one of them would suggest inflating to or more than the stated maximum, so it really doesn't matter now, does it?
I think any of them would be perfectly fine with inflating to the stated maximum. Presumably that's why it exists. As far as I know nobody in this thread is advocating inflating above the stated maximum (even though doing so is likely pretty safe).
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Posthumane on June 18, 2015, 11:56:41 AM
My understanding of bike tire pressure is that higher doesn't equal better.  You want to aim for about 15% deflection of the tire when the rider's weight goes on it.  (You can find charts online for given tires and rider weight).  Higher tire pressures than that actually make you slower because the bike tire wastes more energy bumping up and down along uneven road surfaces.  Your tire is also your suspension on your bike, very high pressures will be painful on your hands and hard on your rims.
This is correct. With bike tires you can calculate what the optimum inflation pressure is based on the size of the tire and the load on it (rear bike tire generally carries more load than front). This is doable with bike tires since they are generally soft and have a round tread section. With car tires it becomes a little more complicated since the construction of the tire (with steel belts and chords in the carcass) cause it to hold a roughly rectangular shape with widely varying pressures.

On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

AWD does nothing to make tires wear unevenly. Perhaps you should talk to a mechanic instead of a friend.

The X pattern for rotation is fine, unless you have directional tires. Directional tires should only be switched from to rear and would be turning the "wrong" way if put on the other side of the vehicle.
Agree with music lover - if you have odd tire wear it is not generally* a result of AWD, and you may have some alignment issues. Misalignment could also cause increased fuel consumption due to tire scrubbing. I rotate my tires front to rear on an AWD vehicle and have no odd wear problems.

Skip the paint test unless you are going to autocross/race and want to see how far the tire folds over. If you want to measure the ground pressure across the tire the best way is probably with a sensitive IR thermometer, but those are usually not cheap and you are probably better off monitoring the tread depth for any discrepancies.  Higher pressures do make a tire run slightly cooler due to less flex, just be aware that this is offset by a reduced contact patch area if you go too high in pressure which will wear faster.


* I say generally as there are some exceptions - some higher performance AWD cars used a viscous coupling limited slip centre differential, and used a slightly different final drive in the rear compared to the front to "load up" the limited slip unit and provide a slightly rearward power bias. This caused increased tire wear.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 12:13:07 PM
On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

AWD does nothing to make tires wear unevenly. Perhaps you should talk to a mechanic instead of a friend.

The X pattern for rotation is fine, unless you have directional tires. Directional tires should only be switched from to rear and would be turning the "wrong" way if put on the other side of the vehicle.

Well I didn't have to talk with anyone to observe the wear patterns.  So yeah,  apparently on my vehicle AWD did in fact result in uneven wear when rotating front to back.  Conversely the X pattern has shown even wear.     So in fact AWD on my vehicle does make tires wear unevenly. 

I'll would let you know how my personal experience with maximum psi works out but I'm planning on selling or parking the beast pretty soon and will likely never reach the usable end of my tire life.   

But I can tell you that everyone I've read (and I've read a lot since posting this thread) that has actually run their tires at or above max psi reported that their tires lasted longer and that they wore dead even.   People who stuck near the 32 psi level experienced more wear on the outer edges of the tires,  more overall wear and lower gas mileage. 

Hey I'm not promoting anything dangerous here folks --- just suggesting to inflate to at or near the max PSI which is well within the safety margin of the tire manufactures.  Use your door or the tire.  Whichever you like.

And yes --- driving a car is much more dangerous than most people think it is  ---

So,

Drive as few miles as needed (there is a direct correlation to number of miles driven and fatalities)
Always wear shoulder and waist belts appropriately adjusted
Always drive alert
Never drive impaired
Never text or phone call while driving
Avoid driving distractions such as eating or listening to radios
Drive defensively
Drive below the posted maximum speed limit (I'll bet more than a few of us break this daily??)
Avoid driving during busy times and at night
Allow a safe distance (1 car length per 10 mph, and almost no one does this)

Remember that driving in the rain is the cause of more accidents than driving in the snow.  (its been raining like an MF here all week!)   Slick roads are very dangerous and I think most people don't know that or forget that.

Yes ----safety first
 



Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: GuitarStv on June 18, 2015, 12:21:07 PM
Driving in rain doesn't cause accidents.  Driving in rain requires more attention.  Mistakes made by vehicle operators still cause all the accidents.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on June 18, 2015, 12:57:43 PM
Well I didn't have to talk with anyone to observe the wear patterns.  So yeah,  apparently on my vehicle AWD did in fact result in uneven wear when rotating front to back.  Conversely the X pattern has shown even wear.     So in fact AWD on my vehicle does make tires wear unevenly.

Are you "that guy" who never admits that he might be wrong??

If the tires on your car are wearing unevenly, then there is a problem either with your car or your driving. AWD that is working correctly does NOT cause uneven tire wear. Tens of millions of people with AWD vehicles have never experienced uneven tired wear.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 01:03:23 PM
On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

AWD does nothing to make tires wear unevenly. Perhaps you should talk to a mechanic instead of a friend.

The X pattern for rotation is fine, unless you have directional tires. Directional tires should only be switched from to rear and would be turning the "wrong" way if put on the other side of the vehicle.

Well I didn't have to talk with anyone to observe the wear patterns.  So yeah,  apparently on my vehicle AWD did in fact result in uneven wear when rotating front to back.  Conversely the X pattern has shown even wear.     So in fact AWD on my vehicle does make tires wear unevenly. 

I'll would let you know how my personal experience with maximum psi works out but I'm planning on selling or parking the beast pretty soon and will likely never reach the usable end of my tire life.   

But I can tell you that everyone I've read (and I've read a lot since posting this thread) that has actually run their tires at or above max psi reported that their tires lasted longer and that they wore dead even.   People who stuck near the 32 psi level experienced more wear on the outer edges of the tires,  more overall wear and lower gas mileage. 

Hey I'm not promoting anything dangerous here folks --- just suggesting to inflate to at or near the max PSI which is well within the safety margin of the tire manufactures.  Use your door or the tire.  Whichever you like.

And yes --- driving a car is much more dangerous than most people think it is  ---

So,

Drive as few miles as needed (there is a direct correlation to number of miles driven and fatalities)
Always wear shoulder and waist belts appropriately adjusted
Always drive alert
Never drive impaired
Never text or phone call while driving
Avoid driving distractions such as eating or listening to radios
Drive defensively
Drive below the posted maximum speed limit (I'll bet more than a few of us break this daily??)Avoid driving during busy times and at night
Allow a safe distance (1 car length per 10 mph, and almost no one does this)

Remember that driving in the rain is the cause of more accidents than driving in the snow.  (its been raining like an MF here all week!)   Slick roads are very dangerous and I think most people don't know that or forget that.

Yes ----safety first
 

Driving UNDER the posted speed limit on a road where most/all other drivers are exceeding it by 5-10mph is MUCH more dangerous than moving with the speed of traffic. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 01:07:53 PM
(https://imgs.xkcd.com/comics/wikipedian_protester.png)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 01:16:31 PM
Grantmeaname --- That was awesome. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 01:20:18 PM
On a related note --- I bought this vehicle from a good friend.   The tires were all oddly worn and he said that the vehicle had always done that due to it being all wheel drive. 

He stated he always rotated front to back.   I questioned this with my tire supplier and he stated that the X pattern was recommended for all wheel drive vehicles using radial tires.   So that is what I have done and I have noted no difference in tire wear.

AWD does nothing to make tires wear unevenly. Perhaps you should talk to a mechanic instead of a friend.

The X pattern for rotation is fine, unless you have directional tires. Directional tires should only be switched from to rear and would be turning the "wrong" way if put on the other side of the vehicle.

Well I didn't have to talk with anyone to observe the wear patterns.  So yeah,  apparently on my vehicle AWD did in fact result in uneven wear when rotating front to back.  Conversely the X pattern has shown even wear.     So in fact AWD on my vehicle does make tires wear unevenly. 

I'll would let you know how my personal experience with maximum psi works out but I'm planning on selling or parking the beast pretty soon and will likely never reach the usable end of my tire life.   

But I can tell you that everyone I've read (and I've read a lot since posting this thread) that has actually run their tires at or above max psi reported that their tires lasted longer and that they wore dead even.   People who stuck near the 32 psi level experienced more wear on the outer edges of the tires,  more overall wear and lower gas mileage. 

Hey I'm not promoting anything dangerous here folks --- just suggesting to inflate to at or near the max PSI which is well within the safety margin of the tire manufactures.  Use your door or the tire.  Whichever you like.

And yes --- driving a car is much more dangerous than most people think it is  ---

So,

Drive as few miles as needed (there is a direct correlation to number of miles driven and fatalities)
Always wear shoulder and waist belts appropriately adjusted
Always drive alert
Never drive impaired
Never text or phone call while driving
Avoid driving distractions such as eating or listening to radios
Drive defensively
Drive below the posted maximum speed limit (I'll bet more than a few of us break this daily??)Avoid driving during busy times and at night
Allow a safe distance (1 car length per 10 mph, and almost no one does this)

Remember that driving in the rain is the cause of more accidents than driving in the snow.  (its been raining like an MF here all week!)   Slick roads are very dangerous and I think most people don't know that or forget that.

Yes ----safety first
 

Driving UNDER the posted speed limit on a road where most/all other drivers are exceeding it by 5-10mph is MUCH more dangerous than moving with the speed of traffic.

I thought our whole discussion here was on the over or under maximum question ---  Now we're encouraging going 12- 25% over if that is what all the cool kids are doing?  ;)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 01:28:01 PM
Grantmeaname --- That was awesome.
It's from xkcd (https://xkcd.com/285/), one of the cleverest webcomics around. Well worth a read if you're not familiar.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 01:32:12 PM
Looks pretty cool.  I just saved to the favs.   Will check it tomorrow and let you know what I think.  I kinda thought it was a Tim Urban thing initially.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 01:59:13 PM
Seriously?  Citation needed?  Do you people have anything between your ears?  What's safer, 10 cars moving in the same direction at 70mph, or 9 cars moving at 70 trying to dodge 1 going 54? 

And no, politically-driven speed limits have nothing to do with engineering-derived PSA limits on tires.  Exceeding one does not have anything to do with exceeding the other. 

Seriously, you guys are fucking with me, right?  There's no way you're this dumb.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 03:01:14 PM
Seriously?  Citation needed?  Do you people have anything between your ears?  What's safer, 10 cars moving in the same direction at 70mph, or 9 cars moving at 70 trying to dodge 1 going 54?
I'm dumb for questioning the 'fact' you pulled out of your ass?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 03:12:56 PM
Seriously?  Citation needed?  Do you people have anything between your ears?  What's safer, 10 cars moving in the same direction at 70mph, or 9 cars moving at 70 trying to dodge 1 going 54?
I'm dumb for questioning the 'fact' you pulled out of your ass?

Roll eyes.  Here's a pretty well cited article I pulled up in 30s on Google.

http://www.ooida.com/IssuesActions/Issues/speed_limiters/documents/Speed-Limiter.pdf
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 03:17:47 PM
That's a press release and it's about something different than your assertion.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 03:20:34 PM
That's a press release and it's about something different than your assertion.

Wat?

It's an article for a trade publication that includes several links to studies.

It's titled

"Differential speed limits make roads less safe
Studies show that a higher variance of vehicle speeds in traffic flow increases the risk of an
accident
"

Which is exactly what I said. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 18, 2015, 03:36:00 PM
You literally just googled a press release from a group of people with a significant financial incentive to drive faster, and it suggests that if they drive faster the roads will get safer. Shocking, no? I would question whether the press release fairly represents the entire literature. Moreover, most of the studies summarized in the biased press release deal specifically with truck-car collisions which means they may be poorly applicable to general circumstances involving two passenger vehicles. I'll also note that of the citations and arguments in the biased press release, the vast majority either boil down to "state X is doing it so your state should too", "it would make our members happy so you should do it", or "here's a change that was made consistent with what we want and no discussion of the results".

Finally, there's a major, obvious methodological flaw in both of the studies that even relate somewhat closely to your assertion. Both studies deal directly with only the one effect of increasing minimum speeds that is potentially favorable - fewer 'interactions' between the general traffic flow and any given slow vehicle. Neither addresses that vehicles moving slowly decrease the average speed of other vehicles and thus all traffic, an effect that could reduce or eliminate the supposed gain from decreasing the interactions. In fact, it's not hard to believe that that effect could be extremely significant. As even your biased press release notes, a 65-70mph increase here in Ohio was enough to increase accident fatalities by a sixth.

Bring a real study next time.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 04:06:51 PM
Holy shite grantmeaname your on your freaking game today!

You could throw in something about the dangers of driving at higher speeds is exponentially more dangerous as you increase speeds.   Most people don't understand that concept and even seasoned drivers perceive very little risk difference between driving at 55 and 75. 

My point was to stick to or below the "maximum" speed limit as many posters here asserted that inflating my tires 4% above maximum was akin to walking into a lions cage with a steak around my neck.  ( I have since acquiesced to just max to appease them)      While the fast driving is an exponentially more dangerous behavior,  mild over inflation at worst is only linearly more dangerous and in many cases safer due to better cornering and minimizing tire overheating potential.

The simple math is that a person who drives slightly below the speed limit will maintaining slightly elevated tire pressure is safer for themselves and other drivers than a person with standard inflation that drives slightly over the speed limit.   

People tend to become confused with the exponential vs. linear comparisons.   

Bottom line slight speeding very dangerous ---- maximum inflation minimum if any increased risk and possibly safer.     
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Chris22 on June 18, 2015, 04:38:15 PM
Bottom line slight speeding very dangerous ---- maximum inflation minimum if any increased risk and possibly safer.   


No.  Holy christ no.  Statistically no one follows the speed limit, so that is very dangerous? 

How about this:  speed limits are set (indirectly) by poiliticians.  Tire pressure maximums are set by engineers.  Which ones are more likely to be correct? 

For fuck's sake.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Posthumane on June 18, 2015, 05:00:49 PM
Well, driving is a very dangerous activity (depending on your definition of very dangerous), so by extension driving over the speed limit is very dangerous. Speed limits are somewhat arbitrary - in some places they are very conservative, in others they are not. Tire pressure specifications for vehicles have a lot of safety factor built into them, as every engineer would know.

Bob, I think this thread has run its useful course, and one of the takeaways that one can glean is that although this is a forum dedicated to critical thinking on financial matters rather than following common rhetoric, that attitude does not necessarily extend beyond financial matters. I suggest posting to automotive/engineering forums on topics like these to get more rounded/researched opinions.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on June 18, 2015, 05:31:02 PM
Agreed,  thanks everyone.   Drove home below speed limit, with tires inflated to max psi and saved 15%/on gas.   Easier than. GEICO!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: milesdividendmd on June 19, 2015, 10:39:38 AM

Bottom line slight speeding very dangerous ---- maximum inflation minimum if any increased risk and possibly safer.   


No.  Holy christ no.  Statistically no one follows the speed limit, so that is very dangerous? 

How about this:  speed limits are set (indirectly) by poiliticians.  Tire pressure maximums are set by engineers.  Which ones are more likely to be correct? 

For fuck's sake.

Any engineer will confirm that speeding is more dangerous than overinflated tires and it's not even close.

Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: RWD on June 19, 2015, 11:58:06 AM

Bottom line slight speeding very dangerous ---- maximum inflation minimum if any increased risk and possibly safer.   


No.  Holy christ no.  Statistically no one follows the speed limit, so that is very dangerous? 

How about this:  speed limits are set (indirectly) by poiliticians.  Tire pressure maximums are set by engineers.  Which ones are more likely to be correct? 

For fuck's sake.

Any engineer will confirm that speeding is more dangerous than overinflated tires and it's not even close.

Really?
http://priceonomics.com/is-every-speed-limit-too-low/
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Guses on June 22, 2015, 02:23:11 PM
I ride on my bike tires inflated to 75 PSI instead of their rated 65.

My car tires are inflated to 51 PSI which is the tires' rated pressure.

Over inflating a tire by 5% it's rated pressure will not suddenly induce catastrophic failure. In fact, here is a quotation from a engineer that worked at a tire company (quote from Pop. Mech.):

"Myth: A tire is in danger of bursting if pressure exceeds the "max press" number on the sidewall.

The truth: The "max press" number has nothing to do with a tire's burst pressure. The "max press" and "max load" numbers indicate the pressure at which the tire will carry the maximum amount of weight. A new, quality tire will not pop at an even multiple of the "max press." I'm sworn to secrecy about the exact burst pressure, but I wouldn't hesitate to double the "max press" of any new passenger-vehicle tire on a new wheel. But hitting a big pothole at super-high pressures may cause a failure."
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Digital Dogma on June 22, 2015, 02:40:43 PM
Id be extremely cautious about overinflating your tires, it will reduce your friction which not only means better MPG, but much worse traction. Emergency braking will get worse, and you could potentially cause a crash because you want a higher mpg.

Having been in a car crash at 45mph, it isnt worth it, Ill find a safer way to save.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Guses on June 22, 2015, 02:52:23 PM
Id be extremely cautious about overinflating your tires, it will reduce your friction which not only means better MPG, but much worse traction. Emergency braking will get worse, and you could potentially cause a crash because you want a higher mpg.

Having been in a car crash at 45mph, it isnt worth it, Ill find a safer way to save.

The best way to avoid car crashes is not to drive.

Since you are obviously still driving, you have accepted the inherent risks involved. The question at this point is if the risk are increased proportionally with the pressure of the tires(I am guessing the answer is "no")?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on June 22, 2015, 03:40:30 PM
You got in that collision due entirely to the car's stopping distance?
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: scottish on June 22, 2015, 04:06:21 PM
My last set of tires wore out in the center of the tread.    The garage I was going to consistently over-inflated them by 7 PSI.   One case does not prove anything, so I'm interested to see how Bob's experiment works over a year or two.    Do you live in the snow belt Bob?   And if so, will you reduce pressure in winter?

For the record, my gas mileage seemed to be better and my traction seemed to be worse.      I now inflate my tires according to the sticker on the door pillar.   (This is what the engineers that designed the vehicle specified, after all.)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: GuitarStv on June 22, 2015, 04:48:29 PM
My last set of tires wore out in the center of the tread.    The garage I was going to consistently over-inflated them by 7 PSI.   One case does not prove anything, so I'm interested to see how Bob's experiment works over a year or two.    Do you live in the snow belt Bob?   And if so, will you reduce pressure in winter?

For the record, my gas mileage seemed to be better and my traction seemed to be worse.      I now inflate my tires according to the sticker on the door pillar.   (This is what the engineers that designed the vehicle specified, after all.)

(http://www.carbibles.com/images/wear_patterns.jpg)

That appears to be what usually happens.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Making Cookies on June 22, 2015, 07:04:10 PM
We increased our fuel economy back in the recession by beginning to car pool 100% of the time and staying closer to home. I run my tire pressures about 3-4 PSI over the car's recommended pressures - and well under the tire's max pressure.

By carpooling (it took several years to get jobs near each other but my wife had a vision crisis so we needed to do that in case she got to a point again where she couldn't drive). We went from ~30K miles pe year to something more like 15K.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: RetiredAt63 on June 28, 2015, 07:25:22 AM
You guys are talking mile per hour, right?  From 55 to 75 is a huge increase!  For me that is going from 88 kph (well below highway limits, they are 100 kph here, well 80 or 90 on secondary routes) to 120 kph. I cruise at about 100 and only get to 120 when I have to pass someone fast (or merge into heavy fast traffic, which is no fun).

I see a huge difference in mileage as my routes shift from 80 to 100, and the rare times when I am cruising at 115 (basically the "keep up with the right hand lane traffic" situation when the other lanes were so busy that I didn't want to push people into them just so they could get past me).

Having just re-inflated the tires on a lawn trailer and a wheel-barrow, I have experienced first-hand the difference between a badly inflated tire (8 psi for max 25psi) versus proper (24 for max 25). Obviously the difference between 20 and 25 would be less, but it would still be there.

Holy shite grantmeaname your on your freaking game today!

You could throw in something about the dangers of driving at higher speeds is exponentially more dangerous as you increase speeds.   Most people don't understand that concept and even seasoned drivers perceive very little risk difference between driving at 55 and 75. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: forummm on August 17, 2015, 02:42:27 PM
Looks like Bob hasn't died in a fiery tire explosion accident....yet..

I gave mine a +2PSI boost today over the mfg rating when I filled them up. They were a bit low. Curious to see if I notice an effect.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on August 17, 2015, 10:07:30 PM
Other than the effect that you're DEAD?
Title: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Seppia on August 17, 2015, 11:17:55 PM
Just read the whole thread, it's surreal.
How a bunch of educated, numbers driven people could advocate over inflating tires above the recommendations of car manufacturers just to save a few pennies, all while ridiculing the only seemingly (to me) sane person that basically states "hey guys if some engineers recommend a range maybe we should stick to it" really escapes me.
The most facepalm-inducing remarks are the "people have over inflated and everything is fine!" 
Well, that proves how safe today's technology is, not that it's a smart thing to do.
I am a diver and no-deco tables have a built in margin of safety. Will you die is you stretch that margin? Most probably not, but the odds are higher of something bad happening.
Over inflating also causes longer braking distance and lower grip, which again seem like very bad things to give up in exchange for a few pennies.
I found particularly disturbing the comment "well what makes driving dangerous is the amount".
Duh. So if I only do a small amount of it I can do it less safely? Because we do recognize that longer braking distance and lower grip are bad right?

To paraphrase the above comment but with a somewhat less life damaging potential recommendation, what really saves money on your gas expenses is the amount of miles you drive.
Drive less but inflate the tires as you should.
If it were only your life I would say go for it, but you share the road with others.
If the recommended range is 34-36 be content with 36 and suck up the extra 15 cents you will pay per month, you can afford them.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on August 18, 2015, 07:49:30 AM
Just read the whole thread, it's surreal.
How a bunch of educated, numbers driven people could advocate over inflating tires above the recommendations of car manufacturers just to save a few pennies, all while ridiculing the only seemingly (to me) sane person that basically states "hey guys if some engineers recommend a range maybe we should stick to it" really escapes me.
The most facepalm-inducing remarks are the "people have over inflated and everything is fine!" 
Well, that proves how safe today's technology is, not that it's a smart thing to do.
I am a diver and no-deco tables have a built in margin of safety. Will you die is you stretch that margin? Most probably not, but the odds are higher of something bad happening.
Over inflating also causes longer braking distance and lower grip, which again seem like very bad things to give up in exchange for a few pennies.
I found particularly disturbing the comment "well what makes driving dangerous is the amount".
Duh. So if I only do a small amount of it I can do it less safely? Because we do recognize that longer braking distance and lower grip are bad right?

To paraphrase the above comment but with a somewhat less life damaging potential recommendation, what really saves money on your gas expenses is the amount of miles you drive.
Drive less but inflate the tires as you should.
If it were only your life I would say go for it, but you share the road with others.
If the recommended range is 34-36 be content with 36 and suck up the extra 15 cents you will pay per month, you can afford them.
I'm still alive,  hyperinflated and saving money.   It's not like I'm risking my life scuba diving or motorcycle riding.   It is more like $400 per year saved for me.    It is more of a comfort issue than safety for me as I always drive slow and rarely slam o n the brakes.    The better cornering with over inflated tires actually adds safety to my driving.   
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Seppia on August 18, 2015, 08:01:29 AM
I see your points and I am sure you are a very safe driver, but I hope there's no negating you are somehow trading safety for money.
You could save $400 driving less :)
Everything we do includes risk (like my scuba diving), and the solution is not to stay home and do nothing all day, but I am not sure I would skip my safety second regulator from my diving equipment because "the main one likely will never fail, plus I have done hundreds of dives and I am still alive, and it saved me $400, and I dive safer than most people do".

Or at the very least I would avoid making fun of those who say it would be better to maybe stick to the recommendations of those who built the damn piece of equipment you are using
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: grantmeaname on August 18, 2015, 11:48:06 AM
You're acting like all decisions that add risk are equally risky. Inflating your tires to the tire manufacturer's recommended cold maximum and diving without a second regulator are similarly risky activities. The fact is we all accept some level of risk at all times by our actions, so such extreme language isn't really a productive way to look at it. I walked down the street today without wearing kneepads, a helmet, gloves, or a condom... The fact that there are some precautions I don't take doesn't make me a reckless maniac, it means that I have weighed the advantages and disadvantages of all the options and settled on one that provides a reasonable mix. 44 psi on tires rated for 44 psi is just another such example.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: zephyr911 on August 18, 2015, 01:29:07 PM
GM based its initial recommendation for my Volt's tires on the 35psi used for the Cruze, because the platform was the same. The additional 900# added by the battery and other novel powertrain components somehow totally escaped their consideration throughout the design and testing phases.

Early Volt drivers found that the recommended pressure produced a high rate of classic underinflation symptoms, including cracked and pitted sidewalls, edge wear, and frequent blowouts. Not surprisingly, increasing the pressure to 40-45 psi evened out the treadwear and reduced catastrophic events. Empirical testing by one pair of owners indicates that 49psi on the more heavily loaded front and 45 on the slightly lighter rear actually produces the most even treadwear.

GM, in response, increased the recommended pressure by about 2psi. Why so little? Community consensus is that they're unwilling to admit to having been so wrong. Look at the recent recalls, and tell me OEMs are never wrong.

Just food for thought. I'm not advocating exceeding the tire's limits, but I don't think anyone here is.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on August 18, 2015, 02:11:35 PM
Just read the whole thread, it's surreal.
How a bunch of educated, numbers driven people could advocate over inflating tires above the recommendations of car manufacturers just to save a few pennies, all while ridiculing the only seemingly (to me) sane person that basically states "hey guys if some engineers recommend a range maybe we should stick to it" really escapes me.
The most facepalm-inducing remarks are the "people have over inflated and everything is fine!" 
Well, that proves how safe today's technology is, not that it's a smart thing to do.
I am a diver and no-deco tables have a built in margin of safety. Will you die is you stretch that margin? Most probably not, but the odds are higher of something bad happening.
Over inflating also causes longer braking distance and lower grip, which again seem like very bad things to give up in exchange for a few pennies.
I found particularly disturbing the comment "well what makes driving dangerous is the amount".
Duh. So if I only do a small amount of it I can do it less safely? Because we do recognize that longer braking distance and lower grip are bad right?

To paraphrase the above comment but with a somewhat less life damaging potential recommendation, what really saves money on your gas expenses is the amount of miles you drive.
Drive less but inflate the tires as you should.
If it were only your life I would say go for it, but you share the road with others.
If the recommended range is 34-36 be content with 36 and suck up the extra 15 cents you will pay per month, you can afford them.
I'm still alive,  hyperinflated and saving money.   It's not like I'm risking my life scuba diving or motorcycle riding.   It is more like $400 per year saved for me.    It is more of a comfort issue than safety for me as I always drive slow and rarely slam o n the brakes.    The better cornering with over inflated tires actually adds safety to my driving.

How can you possibly determine that there is "better" cornering with overinflating tires if you "always drive slow"? To get better traction, one must first approach the limit of traction to find the difference between recommended pressure and overinflation.

Your 15% mileage gains don't add up either:

http://www.popularmechanics.com/cars/a940/4199963/
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: KittyCat on August 18, 2015, 02:13:38 PM
Just came in the say that I am amused by the click-bait, Buzzfeed-like title you have here :)
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Digital Dogma on August 18, 2015, 02:21:34 PM
Seriously?  Citation needed?  Do you people have anything between your ears?  What's safer, 10 cars moving in the same direction at 70mph, or 9 cars moving at 70 trying to dodge 1 going 54? 

And no, politically-driven speed limits have nothing to do with engineering-derived PSA limits on tires.  Exceeding one does not have anything to do with exceeding the other. 

Seriously, you guys are fucking with me, right?  There's no way you're this dumb.
Going 10 miles over the speed limit might have little to no consequence 99.999% of the time you drive, but it could mean the difference between a dead person and an injured person if you hit a pedestrian or cyclist.

Everyone I know has these little 'rules' they make up so they can break the law while driving, but the fact is that nobody else is under any obligation to follow other peoples made up rules. I stop at stop signs instead of rolling through them, does that make me dangerous, or does it make the person behind me who doesn't anticipate this dangerous?

Is someone trying to hypermile on the highway doing 50mph for 2 or 3mpg a bigger problem than someone trying to get to their destination 2 or 3 minutes quicker by speeding at 70mph while dodging slower vehicles? In the end its about the drivers priorities, and chances are they don't align with each-other.

But to address the topic - I'd rather save money on gas by driving a little slower and planning my trips to reduce wasted mileage than by altering my traction by pumping up the tires to max recommended PSI without a heavy load. If MPG were so important to me I'd probably just purchase a smaller/lighter/more efficient vehicle and sell my truck to reap the rewards. Maybe when I get a new job where I can call out during snow storms I'll ditch the 4X4, hope the electric car market really takes off between now and then!
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: KittyCat on August 18, 2015, 02:36:39 PM
Everyone I know has these little 'rules' they make up so they can break the law while driving, but the fact is that nobody else is under any obligation to follow other peoples made up rules. I stop at stop signs instead of rolling through them, does that make me dangerous, or does it make the person behind me who doesn't anticipate this dangerous?
I'm annoyed when I see people rolling through stop signs. Yeah, that's almost everyone where I live. On the other hand, I am elated when someone does come to a full stop. I need something else to which to give my attention.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on August 18, 2015, 03:37:23 PM
Is someone trying to hypermile on the highway doing 50mph for 2 or 3mpg a bigger problem than someone trying to get to their destination 2 or 3 minutes quicker by speeding at 70mph while dodging slower vehicles? In the end its about the drivers priorities, and chances are they don't align with each-other.

If someone is going 50mph and everyone else is going 70, then the person going 50 is a problem for everyone else. Conversely, if everyone is going 50 and one person is going 70, then the person going 70 could be a problem, but not always. That's because everyone has to maneuver/change lanes to go around the car going 50, whereas the person travelling 70 doesn't make everyone else adjust for them...they can pass slower drives if they are in the slow lane and the faster driver is in the passing lane.

When you blame it on people wanting to get there 2 or 3 minutes faster, you're completely missing the point. Within reason, the safest speed on a highway is to be travelling close to the same speed as other drivers...not exactly the same speed because then you get the person in the left lane blocking traffic. But, if traffic in the left lane is going 2-3 mph faster than the right lane, traffic will move smoothly.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on August 18, 2015, 03:47:40 PM
Everyone I know has these little 'rules' they make up so they can break the law while driving, but the fact is that nobody else is under any obligation to follow other peoples made up rules. I stop at stop signs instead of rolling through them, does that make me dangerous, or does it make the person behind me who doesn't anticipate this dangerous?
I'm annoyed when I see people rolling through stop signs. Yeah, that's almost everyone where I live. On the other hand, I am elated when someone does come to a full stop. I need something else to which to give my attention.

Rolling through a stop sign is a non-issue if no one is coming, and also a waste of gas. In England, signs that say "give way" are more common than stop signs. People simply slowed down enough to ensure it was safe to proceed. But, then again, they are far better drivers than North America.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: KittyCat on August 18, 2015, 04:29:24 PM
Rolling through a stop sign is a non-issue if no one is coming, and also a waste of gas. In England, signs that say "give way" are more common than stop signs. People simply slowed down enough to ensure it was safe to proceed. But, then again, they are far better drivers than North America.
The problem is, people assume that no one is coming, and oftentimes do not bother checking before rolling, even at turns on t intersections. Perhaps your experiences have been different from mine, but I do not trust the drivers around the area where I am.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Joggernot on August 18, 2015, 04:45:10 PM
AIUI: Manufacturers set tire pressure for ride comfort, not fuel economy.  I have run max sidewall pressure on two vehicles (car and pickup) for many years with no problem.  Max sidewall is not recommended by me.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: music lover on August 18, 2015, 05:03:30 PM
AIUI: Manufacturers set tire pressure for ride comfort, not fuel economy.  I have run max sidewall pressure on two vehicles (car and pickup) for many years with no problem.  Max sidewall is not recommended by me.

They set tire pressure for both comfort and fuel economy, and I'm pretty sure the techs working at major auto manufacturers have a pretty good idea what they're doing. The people that made the tire set the maximum recommended pressure, but any particular tire can end up on dozens of different vehicles, which is why the car comes with a sticker that has a different recommended pressure.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Nubs on August 18, 2015, 05:11:26 PM
Yeah,  I know,  funny huh?

So I checked my tires on the 1999 Mercury Mountaineer.  Damn 32 lbs!   Max inflate rated at 44 lbs.   I filled those babies up to 46 lbs.

Took daughter home to her moms house which is about 45 miles at 32 lbs and MPG 18.5 (I have a digital tracker)   Filled up the air.   Return trip 21.4 MPG.

That is a 15% increase in MPG!  Our annual car gas bill for 2 cars runs about $2,400 (yeah, I know I'm researching higher MPG cars)   So this little trick will save us $400 per year if we do nothing different. 

So yeah,   check your tires and don't be shy about going a tad over the max inflate.    By the way,  hypermilers increase their Prius mileage to 65 mpg simply by overinflating a tad.  Bike riders take note as well --- you could be peddling with 15% less effort. 


YMMV!

I don't do too much peddling on my bike, but I do like the sound of using 15% less effort when I pedal home tonight. . . or going faster.  ( :
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: The_Dude on August 18, 2015, 05:13:48 PM
Just thought I would throw out my own anecdotal report.

Back around 2000 I ran a set of BFG KDW tires (255 width) at 44 PSI and it killed them much faster than when I ran the next set at 35 PSI.  The set ran at 44 PSI all went bald in the middle 1/3 of the tire and lasted between about 66% of the next set of tires. 

To me the moral of the story is that is greatly depends on the type of the tire (and I imagine width) on how much, if any, extra wear in the center is created by over inflation. 

Oh, one more anecdotal story since it was brought up earlier.  I am an active autocrosser.  My current tire of choice is the Falken Azenis tire which is known for a super stiff sidewall.  I run these tires much LOWER for maximum cornering grip.  I'm not disputing that many autocrossers inflate their tires above the recommended 35 PSI for maximum grip, but again, it depends on the tire. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on August 19, 2015, 08:31:54 AM
GM based its initial recommendation for my Volt's tires on the 35psi used for the Cruze, because the platform was the same. The additional 900# added by the battery and other novel powertrain components somehow totally escaped their consideration throughout the design and testing phases.

Early Volt drivers found that the recommended pressure produced a high rate of classic underinflation symptoms, including cracked and pitted sidewalls, edge wear, and frequent blowouts. Not surprisingly, increasing the pressure to 40-45 psi evened out the treadwear and reduced catastrophic events. Empirical testing by one pair of owners indicates that 49psi on the more heavily loaded front and 45 on the slightly lighter rear actually produces the most even treadwear.

GM, in response, increased the recommended pressure by about 2psi. Why so little? Community consensus is that they're unwilling to admit to having been so wrong. Look at the recent recalls, and tell me OEMs are never wrong.

Just food for thought. I'm not advocating exceeding the tire's limits, but I don't think anyone here is.

Thanks for that --- I'm really surprised at the number of hyperbolic negative responses here.   In a world were virtually everyone I know consistently exceeds the speed limit by 10% (maximum "legal" speed) it is as if I committed a crime and am endangering everyone on the road by maxing out my tires on my 4,000 pound vehicle.     Yeah,  I'll switch it out to a much more fuel efficient car someday.  And then I'll max the tires out on that car as well.

And yes 15% was my personal tested amount on that particular day.   (thanks to the posters who enjoyed my click bait!) I haven't bothered to further test as that was a pretty good indicator run day. 

So far one of my tires has worn more so on the inside of the tread.  While you might think this is a bad thing, when I bought the truck all 4 were worn on the inside.  My friend owned the truck for 10 or 11 years and always had this issue with the all wheel drive Mountaineer.   So it appears that my tread wear has actually improved.    Most of the sites I referenced indicated that in general tread wear is less with high inflation.  That makes sense as there is less flexing of the rubber.

I have put maybe 5-6K on the truck since starting this and haven't had any handling issue or dangerous stops in that time.  As I say,  I always try to anticipate stops well ahead and an increase in stopping distance appears to be the primary negative mentioned on the tire sites.   I have noticed,  and perhaps I'm wrong,  that I need or want to drive much slower on rocky bumpy roads.  That is about 5% of my summer time driving. 

I'm going to use one more trick and have that worn tire reversed on the rim.   Please don't beat me up over that. 
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Ashyukun on August 19, 2015, 09:21:50 AM
I don't do too much peddling on my bike, but I do like the sound of using 15% less effort when I pedal home tonight. . . or going faster.  ( :
The thing with bike tires, like many people with car tires, is that they're often not properly inflated even to what is recommended. On my road bike, that's between 90-100 psi, which I have to top off every weekend to keep up in the optimal range. There is a DISTINCT difference in ease of riding when they're properly inflated, though also a distinct roughness of the ride on my old solid-frame racing bike.

Quote from: Bob W
I'm going to use one more trick and have that worn tire reversed on the rim.   Please don't beat me up over that. 

As long as they're not directional-tread tires, there's nothing at all wrong with that. Correcting the alignment/inflation that caused it in the first place would be better (;P) , but that is a trick that auto-xers will use to extend the life of tires that wear very unevenly due to high cornering loads and it works well enough as long as there's not damage to the underlying structure of the tire.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: GuitarStv on August 19, 2015, 10:13:06 AM
I don't do too much peddling on my bike, but I do like the sound of using 15% less effort when I pedal home tonight. . . or going faster.  ( :
The thing with bike tires, like many people with car tires, is that they're often not properly inflated even to what is recommended. On my road bike, that's between 90-100 psi, which I have to top off every weekend to keep up in the optimal range. There is a DISTINCT difference in ease of riding when they're properly inflated, though also a distinct roughness of the ride on my old solid-frame racing bike.

Real recommended tire pressure depends on rider weight, type of riding, and tire size.  The front and rear tires should never be pumped to the same number.  The rear tire of a 250 lb man on an upright bike requires much higher pressures than the rear tire of a 90 lb woman on a road bike, even assuming they're using the same brand, model, and width.  The number on the casing doesn't really have anything to do with the pressure you should ride at.

As as been mentioned further up thread somewhere, it's also possible to inflate bike tires beyond where there's any real advantage regarding rolling efficiency.
Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Guses on August 19, 2015, 10:35:38 AM
AIUI: Manufacturers set tire pressure for ride comfort, not fuel economy.  I have run max sidewall pressure on two vehicles (car and pickup) for many years with no problem.  Max sidewall is not recommended by me.

They set tire pressure for both comfort and fuel economy, and I'm pretty sure the techs working at major auto manufacturers have a pretty good idea what they're doing. The people that made the tire set the maximum recommended pressure, but any particular tire can end up on dozens of different vehicles, which is why the car comes with a sticker that has a different recommended pressure.

Scroll to my post somewhere in the middle of the 2nd page. I provide a link to an engineer that actually worked in the tire business. He states that the max sidewall pressure is not the "danger zone not to be exceeded" and that tires are not at a danger to explode unless you exceed the psi by multiples of the max recommendation. Increasing the pressure over the max sidewall point is just giving you less comfort for less rolling resistance.

Those claiming that it is unsafe should consider that low rolling resistance tires are exactly the same as overinflating a tire by a few psi. Low rolling resistance = less grippy tires. Blowouts related to overinflation by a few PSI are a myth.

The "safety aspect" is really a red herring. If you believe this, you should also advocate for much lower speed limits. Consider this: the difference in stopping distance comparing one car with max spec inflation tire versus the same care with max specs inflation +5 psi is laughably small. On the other hand going 5 MPH faster significantly increases stopping distance.

I am too lazy to link a graph, but a quick google will show you that the relationship is exponential.

Title: Re: This One Simple Trick Will Increase Gas Mileage by 15%!!
Post by: Bob W on August 19, 2015, 11:00:29 AM
AIUI: Manufacturers set tire pressure for ride comfort, not fuel economy.  I have run max sidewall pressure on two vehicles (car and pickup) for many years with no problem.  Max sidewall is not recommended by me.

They set tire pressure for both comfort and fuel economy, and I'm pretty sure the techs working at major auto manufacturers have a pretty good idea what they're doing. The people that made the tire set the maximum recommended pressure, but any particular tire can end up on dozens of different vehicles, which is why the car comes with a sticker that has a different recommended pressure.

Scroll to my post somewhere in the middle of the 2nd page. I provide a link to an engineer that actually worked in the tire business. He states that the max sidewall pressure is not the "danger zone not to be exceeded" and that tires are not at a danger to explode unless you exceed the psi by multiples of the max recommendation. Increasing the pressure over the max sidewall point is just giving you less comfort for less rolling resistance.

Those claiming that it is unsafe should consider that low rolling resistance tires are exactly the same as overinflating a tire by a few psi. Low rolling resistance = less grippy tires. Blowouts related to overinflation by a few PSI are a myth.

The "safety aspect" is really a red herring. If you believe this, you should also advocate for much lower speed limits. Consider this: the difference in stopping distance comparing one car with max spec inflation tire versus the same care with max specs inflation +5 psi is laughably small. On the other hand going 5 MPH faster significantly increases stopping distance.

I am too lazy to link a graph, but a quick google will show you that the relationship is exponential.

All true.  You would think that there would be a national push for over inflation.   Can you imagine the impact a 10% reduction in gas usage would have on the economy?  It is not a small thing.  Take the $400 per year we will save and multiply by 150 million and your looking at a 60 billion dollars "one simple trick."