Author Topic: New spare tire?  (Read 2438 times)

lizzzi

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New spare tire?
« on: April 06, 2015, 11:19:59 AM »
When buying four new tires for a car that has a full size spare (never used), is it necessary to buy a fifth, matching new tire to be the new spare?

velocistar237

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Re: New spare tire?
« Reply #1 on: April 06, 2015, 11:24:35 AM »
From Hypermiling: Expert driving to save 25% on gas:

Quote
In a 3,000 pound car, each 30 pounds you slice from the weight cuts your weight by 1% and increases your fuel efficiency by about the same amount. It also improves acceleration and handling. I always start by removing the spare tire, jack, and related metal accessories from the trunk. There’s 50 pounds, and a bunch more trunk space. I do add in a can of fix-a-flat tire repair spray. Spare tires are good if you’re traveling alone through Death Valley or South America, but for local errands, in a world with cell phones and internet access, I haven’t worried one bit about my own habit of never carrying spares for the past 20 years (I have had a few flat tires over the years, but always just slow leaks that I discovered in my driveway – an embedded nail or similar).

Even with new tires, the spare doesn't have to match if you're just using it as a spare and not as a permanent replacement.

forummm

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Re: New spare tire?
« Reply #2 on: April 06, 2015, 11:34:23 AM »
And your tires don't generally need to "match", they just need to have equivalent ratings. It can improve resale value slightly if they do match. You'd probably want to have very similar tires for the front 2 and for the back 2. But as long as they are the right size and rating for your vehicle, they don't have to have the same brand, etc.

lizzzi

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Re: New spare tire?
« Reply #3 on: April 06, 2015, 11:39:36 AM »
I do a lot of driving alone through the out-of-state boonies, so am more comfortable having the spare tire in the car. I will get some of that tire sealant spray, too--thanks for the reminder. I would only plan to use the spare until I could have the flat tire repaired. The tire dealers seem to encourage buying five new tires--but of course, they would!

gimp

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Re: New spare tire?
« Reply #4 on: April 06, 2015, 12:48:01 PM »
The idea of removing emergency equipment for a 1% boost in gas efficiency is fucking insane, and idiotic.

Not only that, but it's based on flawed logic. 1% weight reduction does not equal 1% gas use reduction. For acceleration - sure! For highway use - no. A large amount of the gas you spend at cruising speed is used to fight air resistance. Guess what doesn't change when you remove your emergency equipment?

So I would love to see some actual numbers, not just some bullshit assertion. It will never happen, of course, because of placebo effect, and because actual numbers take a great many miles to generate.

With all that said, here's the real answer. A matching tire is not necessary. Hell, you can drive on a half-sized spare, you can certainly drive on a full-sized spare. What's important is that it has roughly the same or better maximum characteristics (speed, loading, etc) if you are anywhere near that maximum. For most people's driving, it's not even an issue. Will there be abnormal tread wear? Probably. Will your handling be slightly off? Probably. Will it be enough to really notice? Not really. You may be hardly worse off than the case of 3 used tires + 1 new matching tire (since one assumes a tire pops after you've been driving a bunch, and all four on the ground are somewhat worn.)

In short, it doesn't matter for the distances needed to get to wherever you're going for a while until you can make it to a tire shop to do a replacement. It would matter if you plan to drive thousands of miles, but less for safety, and more for just treadwear and handling.

Necessary, no; needed, only if you plan on using it permanently.

velocistar237

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Re: New spare tire?
« Reply #5 on: April 06, 2015, 01:13:14 PM »
The idea of removing emergency equipment for a 1% boost in gas efficiency is fucking insane, and idiotic.

Not only that, but it's based on flawed logic. 1% weight reduction does not equal 1% gas use reduction. For acceleration - sure! For highway use - no. A large amount of the gas you spend at cruising speed is used to fight air resistance. Guess what doesn't change when you remove your emergency equipment?

So I would love to see some actual numbers, not just some bullshit assertion. It will never happen, of course, because of placebo effect, and because actual numbers take a great many miles to generate.

Yeah, I didn't really examine that one before putting it out there. A quick search pulls up a 1-2% improvement for a 5% weight reduction.