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Old 03-15-19, 06:06 AM
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rhm
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Originally Posted by Salubrious View Post
There is plenty of data on this ...

Here's a nice article on the issue:

https://ridefar.info/2017/02/crank-l...ance-cyclists/
Thanks for the link! That is an interesting article, and pretty well sums up the available literature.

Nonetheless, I do not agree, that "there is plenty of data." There are plenty of anecdotes, and plenty of attempts to apply mathematical formulas to anecdotal evidence, but very little actual data. So, for example, Kirby Palm (Bicycle Crank Length Derivation) writes "After much qualitative observation and some informal testing, I have concluded that: The standard crank length of 170mm is optimum for a cyclist with a 31-inch inseam."

"Much qualitative observation and some informal testing"? Why do I suspect he means most bikes come with 170 mm cranks and most people are fine with that, so that must be the right size for average size people? I doubt he spent much time trying cranks that were a whole lot longer, or a whole lot shorter, than 170 mm.

I would like to see the results from experiments using a range of crank arm lengths so wide that there is an actual decline in performance at the extremes. I mean, if there is little measurable difference between 170's and 165's, they should try 150's... and 135's, and 120's, and so on. I would like to see power output, heart rate data, etc, for the full range of possible rider sizes, all of them using a full range of crank arm lengths-- not just the ones commonly available.

I think we can safely assume there is an ideal size crank arm for each rider, and that power or efficiency or something will drop off dramatically when using cranks that are too short or too long. But I have never seen test data that clearly identified what is "too short." I assume that even for tall riders it will be much shorter than 165 mm; but that assumption, along with all the other assumptions, really should be tested.
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