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Old 03-29-19, 01:03 PM
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rhm
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Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...

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Originally Posted by Carbonfiberboy
I guess I don't understand the criticism. You don't think cranks should be proportional to leg length or what? I have a 31.5" inseam, so 172.5 cranks by the 5.48 formula, and ride 170 on my singles and 175 on our tandem, both comfortably. You think my wife should ride shorter than 148 cranks? Of course making crank length proportional to leg length immediately leads to non-industry-standard BB heights for tall riders. But why should there be an industry standard BB height for everyone? What sense does that make, since every frame size has different geometry anyway? I ride with a long-legged 6'5" guy who's on 180 cranks, and looks ridiculous with them, like a clown bike and it's a custom bike, too.

There are some interesting articles on proportional crank length, all worth reading, here:
https://www.stevehoggbikefitting.com...gth-which-one/
https://www.trainingpeaks.com/blog/t...-crank-length/
https://www.velonews.com/2003/11/bik...nk-length_5257

Note that while proportional cranks lengths seem to be universally advocated, the formula is very much in question.

Thus if those interested in commenting would be so kind as to do the following, it would be very helpful: Measure your inseam barefoot by standing against a wall, shoving a clipboard up against your pubic bone, and measuring the distance from its top to the floor. Take that number in inches, divide it into your favored crank length in mm and report that ratio!

Thanks.
Starting with your last question, I measure my inseam at 34 inches. Most of my bikes have 165 mm cranks, so if I'm doing this right, I get 4.85.

I won't say 165 is my favored crank. That's just the shortest widely available crank. I often ride old bikes with old gear on them, and it's rare to find anything shorter than 165 (I do have 160's on three bikes, two of them fixies). I have used 152's, 145's, and 140's in the past, and my only complaint was that they made my other bikes feel funny with their long 165 mm cranks.

I totally agree, in theory, that one could determine a formula by which we could specify a crank arm length that's statistically most likely to be "ideal" for a person based on some bodily measurement. And I agree that inseam is a good place to start.

But I'm not going to tell anyone he or she should use shorter cranks. In most cases I doubt it makes much difference. You ride cranks that are proportionally a lot longer than mine, and you are faster than I, but I don't think your longer cranks are the reason you're faster than I. So should you ride something other than what you like? No, I don't think so. If you were a novice, I'd recommend shorter cranks for you, but you have found something that works for you, and I don't see any reason to change that. 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.

I do believe that riders would in general be a little better off using shorter cranks, and I know it's not going to happen. It doesn't make a big enough difference. It wouldn't make economic sense for factories to make a full range of possible crank arm lengths, frames with a variety of bottom bracket heights, and all the variables.

A few posts back I pointed out that people of all sizes are able to go up and down the same flight of stairs (typical stair rise around 175 mm) without complaining. There's a certain socialism in that -- stairs have to be designed to work for all of society. So the same applies to CitiBike and other bike share programs. There's good reason to stick with 170 mm cranks by default. I just don't consider them ideal.

Originally Posted by Carbonfiberboy
As my TrainingPeaks link points out, shorter cranks can be faster seated, but one runs into issues with OOS efforts on very steep pitches and sprinting. where shorter cranks reduce leverage and it's not efficient or sometimes even possible to just pedal faster.
Yes, all true. 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.
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Last edited by rhm; 03-29-19 at 01:13 PM.
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