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165mm vs 170mm cranks for Randonnuering

Old 04-30-19, 11:35 AM
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Originally Posted by ThermionicScott View Post

P.S. Now that you bring up BB height, I wouldn't be surprised if part of the reason for the industry standardizing on 170mm cranks is to fix that aspect of frame manufacture, rather than needing to offer a zillion more frames with varying BB heights. If a bike company were sympathetic to the need for a wider range of crank lengths, perhaps they could scale the BB height with the frame size. Maybe some makers do already...
My GF complains often that she can't put a toe down to balance herself on any of her bikes. She has to get off the seat at a stop. This is because even though she's on the shortest Trek frame made, its bottom bracket is the same height as mine. The industry really doesn't support shorter people wanting to ride bikes. Some of this has to do with wheel sizes and how geometry changes affect handling; but to me it just sounds like they don't want to do the harder work of figuring it out.
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Old 04-30-19, 12:15 PM
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the industry is deathly afraid of pedal strike. Sure, it can be dangerous in extreme cases, but it usually isn't that bad. I have a whole collection of vintage pedals with the bottom outside edge totally messed up. I have never gone down due to pedal strike
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Old 04-30-19, 06:27 PM
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Originally Posted by rhm View Post
<snip>On the other hand, I'm pretty confident you could switch your wife's crank onto your bike and you'd get used to them in a short time and get to like them just fine. But it's a tandem stoker crank, and the pedal threads will be backward, so never mind that.
You often mention that it's important to spend some time out of the saddle on all rides (I hope I'm not confusing you with someone else), and it's good advice. Shorter cranks do tend to discourage the rider from getting out of the saddle, and that's not a good thing. Anyone investigating 'ideal crank arm length' would need to keep this in mind. Whatever the ideal crank arm length is, it's going to be a compromise.
So far I haven't ridden a tandem on which normal L and R pedals didn't fit all 4 cranks normally. Specially threaded tandem cranks may be ancient history. In any case, I already spin 100 comfortably on the 175s, and am not about to give up the OOS leverage or the steep stuff seated leverage. I don't see what shorter cranks could improve.

We've now ridden a couple hundred miles with the 151mm stoker cranks. It became obvious that we were much slower on steep climbs where our cadence dropped below ~80. On the good side, Stoker likes them. On the bad side, she's cramped more with the shorter cranks, something I did not expect, but because of the shorter lever arm, she has to push down harder on the steep stuff to produce the same power. On the good side, she can stay up a little longer when we stand. On the bike mods side, I've put a 40T cassette on, so now our lowest gear is 26 X 40. That gets us up the 15% grades we could not climb with the shorter stoker cranks and a 34T cassette.

On our tandem, captain's ratio is 5.56 and Stoker's is 5.59. On my single, my ratio is 5.40. Stoker's previous ratio was 6.30.
Results matter
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Old 05-27-19, 02:45 PM
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Iím never riding anything shorter than 200mm cranks again if I have a choice.
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Old 08-16-19, 01:22 PM
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Just did conversion #4 to short cranks. All for friends. In each case warned that it was pure guesswork. Three of four had very short test rides on a non-ideal test bike. Each rider is completely amazed at how well 150 or 152 cranks work. For them. Promising it will work for you would be silly. But if you are curious or have any reason to think you are a good candidate for shorter cranks it is worth a try.
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Old 08-18-19, 06:15 AM
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For an extreme long crank argument, check out this 1969 Bicycling article posted in the C&V forum: 50 Years Ago: August 1969 in Bicycling! magazine

For what itís worth, Iím in the short crank camp because my hips arenít very flexible. With 170s I have a hard time getting over the top of the pedal stroke when Iím on the drops because my hip canít close far enough. The natural tendency is to compensate by rolling the pelvis pack and bending with the spine rather than hip, which isnít good for the lower back.
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