Interestingly there is an interaction with leg length, although it definitely isn't as clear as it would appear.
So far we have found, zero riders with FTP over 350 choose short cranks, as they get higher their dislike of them appears greater.
However all of these riders were happy enough on 165s, apart from the guys with FTPs over 400.
For these 170-175 felt optimal.
Leg length was a factor in that athletes with FTPs of 300-350 but with longer legs struggled with the short cranks, but were ok on 165s.
We had athletes at lower powers with long legs fine on shorter cranks. (150-160).
We are currently doing some torque analysis, but it seems to related to the ability to apply a considerable amount of torque at an appropriate cadence in a constrained position (aero). With the short cranks the window is smaller, which only seemed to have a significant effect once we were getting into high power realms.
What is "appropriate cadence"? Does it get higher as crank length gets shorter?
I also think that you need to include some metric for the appropriateness of the short crank to the fit of the rider. I would not be surprised if in the population of your riders, as FTP goes up, height goes up and therefore the usefulness of a short crank for fit goes down.
Ed O'Malley www.VeloVetta.com
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