Author Topic: Unipedal Drive, or What to do when Life gives you lemons.  (Read 10653 times)

prefixcactus

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Unipedal Drive, or What to do when Life gives you lemons.
« on: May 06, 2016, 02:42:02 AM »
The first commute of may was sure interesting... Like the "Interesting times" in that ancient Chinese curse.

About a week ago I bought a set of new all-metal pedals to replace the worn-out stock plastic ones that came with the bike. I probably did something wrong at some point because when I unscrewed the left one it came out taking about half the crankarm threads with it (Which is what generally tends to happen in any systematically stressed joint between two metals of radically different hardness: the harder one eats through the softer one. Apparently whoever made the decision to use 100% alu crankarms in the design disregarded that particular bit of engineering wisdom).

[click on the images for a larger version]
This did not prevent me from installing the new pedals anyway, since the other half of the threads was intact and held the pedal nicely.
The bike performed awesomely after that. Until today, that is. My bike has a pretty small pedal-to-ground clearance, a natural result of it being a hybrid, so it tends to scrape the ground with the pedals on steep turns. Usually I put the inner pedal into the topmost position before turning to avoid this, but not this time. And it was a left turn.

The effect was not immediately noticeable, but as the now-free steel threads ate an ever-bigger hole through the aluminum (the progress can be clearly seen by comparing the two images below), it became worse as I rode on in the hopes that the arrangement will at least last until my destination. Those hopes were destroyed by the pedal falling out about halfway there. Oops.


So, what do you do with a bike with only one pedal? Why, you ride it!
Getting the hang of powering a bike with a single pedal was a bit tricky. Overall, you do it as follows (assuming missing left pedal):
  • Push the pedal with right leg
  • As the pedal nears the bottom, guide it as far as you could, using its grippiness
  • As it passes the bottommost position, step with left leg on the left crankarm and try to pull the right pedal up
  • The tricky part is getting the remaining pedal over the top. If it stops before reaching it, it will fall down backwards under its own weight (without a second pedal to counterbalance it)
First, you just struggle with trying to not let the remaining pedal fall backwards. Then you finally get the hang of it and start going in single strokes with your right leg, bringing the pedal back to the top with your left. Then you start doing it nonstop. Then you learn to actually apply some force in the no-pedal portion of the cycle. Then you learn to switch gears while doing all this. And then you carry on with the rest of your commute LIKE A BADASS. Including a couple-kilometer-long 5 climb. And end up taking only ten minutes more getting to your destination than your average.

In fact, this was one of the funnest rides I've ever had, propelling myself in this crazy way. It's almost worth intentionally unscrewing a pedal just to try it.

I am going to replace the crankarm (unless I somehow miraculously manage to find a way to add material to this thing and then cut a 9/16" thread here in metricland), since despite the fun this mode of transportation is quite inefficient. Also, 5 slopes are about the limit and Moscow is a moderately hilly city, with way more than that in some spots.

To summarize, when Life gives you lemons, you:
  • Do not make Lemonade
  • Kick Life's ass (with just one leg) and make it take the lemons back
  • Make fun of Life for even attempting to do that to you
  • Walk away like the badass you are.

Good day to you all, and kick ass.

GuitarStv

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #1 on: May 06, 2016, 09:47:19 AM »
There's nothing wrong with using steel and aluminum on a bike.  It's done all the time.  It's important to grease threads though, and ensure that everything is tightened to proper torque.

It's also very common for people to wreck the threads of a bike pedal by cross threading them . . . because one pedal is reverse threaded.  If you grab a pedal at random and try to tighten it, you've got 50-50 odds of wrecking your crank.  A good rule of thumb is to only start threading a pedal by finger tightening.  If you need more pressure than that, you are probably fucking something up.

big_slacker

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #2 on: May 06, 2016, 02:48:13 PM »
It's also very common for people to wreck the threads of a bike pedal by cross threading them . . . because one pedal is reverse threaded.  If you grab a pedal at random and try to tighten it, you've got 50-50 odds of wrecking your crank.  A good rule of thumb is to only start threading a pedal by finger tightening.  If you need more pressure than that, you are probably fucking something up.

This is what I thought the moment I saw that crank. Cross thread or no grease. I've done the same when I was younger and dumber. Not that I'm saying that's absolutely what happened here, but it looks like it.

I always put some grease around the threads on the cranks and the pedals. Hand tighten them with only a final torque once they're all the way on.

Props on finishing that ride the manly way!

innkeeper77

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #3 on: May 06, 2016, 04:31:01 PM »
You can fix the crank arm; Look up "helicoil" (brief response, I'm at work...)

I did the same thing to mine. The helicoil fix has held up great! Be sure to really richen it down, loose pedals have a tendency to strip out the holes like that.

prefixcactus

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #4 on: May 07, 2016, 04:53:56 AM »
There's nothing wrong with using steel and aluminum on a bike.  It's done all the time. 
I know it's done all the time, duh. But usually it's steel axles that go through the aluminum frame; further than that they're usually connected via bearings which make the connection even more foolproof. The problems start when there's significant pressure (small area of contact or uneven distribution). Threads are a pretty good candidate for creating such a situation.

Quote
It's important to grease threads though, and ensure that everything is tightened to proper torque.

It's also very common for people to wreck the threads of a bike pedal by cross threading them . . . because one pedal is reverse threaded.  If you grab a pedal at random and try to tighten it, you've got 50-50 odds of wrecking your crank.  A good rule of thumb is to only start threading a pedal by finger tightening.  If you need more pressure than that, you are probably fucking something up.

Well, I did get confused at first, trying to unscrew the left pedal in [what turned out to be] the wrong direction... (although I actually found the markings telling me which pedal was which first. It might've been this excessive tightening, or it might've been the lack of grease, I don't know. Anyway, I've called my local workshop and they said there exists some kind of special threaded insert for such cases and redirected me to another shop (apparently there are only two shops in moscow that actually stock them). Now I'll just have to invent a way to get my bike there without wasting too much time.


Heckler

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #5 on: May 07, 2016, 08:23:12 AM »
Careful with rotation direction when installing or removing pedals!  One of them is a reverse thread to prevent it from unthreading if the bearings seize while you are riding. 

Heckler

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dilinger

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #7 on: May 07, 2016, 10:56:12 AM »
A new (left) crank is like $15.  I probably would've replaced it immediately after seeing the damaged threads (as opposed to risking damage to a more expensive pedal).  However, now that it's even more broken - don't try to fix it.  Just get a new crank arm!

prefixcactus

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #8 on: May 07, 2016, 05:09:32 PM »
A new (left) crank is like $15.  I probably would've replaced it immediately after seeing the damaged threads (as opposed to risking damage to a more expensive pedal).  However, now that it's even more broken - don't try to fix it.  Just get a new crank arm!

Given that the pedal axle is made of steel and the crank of alu, it is nigh-impossible to damage the pedal with the crank. Anyway, I actually wanted to order a new one and ride with the damaged one until it arrived unfortunately local stores don't seem to stock any of this particular model. Now, though, I'll probably get the insert. Cheaper and I'll get my bike back faster. Also a great opportunity to get the wheels re-tensioned and adjusted, something I've been wanting to do for some time now (but didn't want to part with the bike for too long, heh). Maybe I'll order a different pair (now that I know they come in varying lengths) later and swap it anyway, but we'll see.

Heckler

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #9 on: May 08, 2016, 12:01:53 PM »
it is nigh-impossible to damage the pedal with the crank.

I have, over the past fifteen years, owned at least a dozen bikes with alu cranks and steel pedals and switch out my pedals a dozen times per year.  Never have I damaged the crank arm threads.

Use some grease on the threads, don't over tighten and make sure to be turning the threads in the correct direction and enjoy your new cranks (which you really should invest in for safety sake)

prefixcactus

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Re: Unipedal Drive, or What to do when Life gives you lemons.
« Reply #10 on: May 08, 2016, 03:22:21 PM »
I have, over the past fifteen years, owned at least a dozen bikes with alu cranks and steel pedals and switch out my pedals a dozen times per year.  Never have I damaged the crank arm threads.
...but why would you need a new bike every 15 months? And switch pedals every month? That seems mighty wasteful.

Quote
Use some grease on the threads, don't over tighten and make sure to be turning the threads in the correct direction and enjoy your new cranks (which you really should invest in for safety sake)
Well, yeah, lesson learned ^.^
As for investing in a new pair... We'll see. What's that about the safety, anyway?