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Dr. James C. Martin, PhD research shows that there is little difference in efficiencies between your current crank arm length and any other commercially available crank arm length.

There are several other interesting finds from his research.

In summary: Common crank sizes are nearly all equal in efficiencies. Cranks size can be chosen for reasons such as ground clearance for cornering/obstacles (shorter), aerodynamics (shorter), or rehabilitation/flexibility (longer). Sprinting 120 rpm is best. 60 rpm is better than 100 rpm aerobically (generally lower cadences are more efficient than higher). Natural pedal stroke is best (do not pull up), crank length has no effect on fatigue, no effect on metabolic efficiencies and very small effect on maximum power. A big gear sprint is better than a small gear sprint (for 30seconds) .

For some illustrations and further comment see: My World From a Bicycle: Dude your crank length's fine, you just need to gear up

I hope this helpful.

Regards,
David Henderson
 

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GiddyUp
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This is an awesome post, I'll check out that book. I have been wondering how a fitter arrives at your optimal size.
 

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I'll be on the other side of the fence on this one; there IS a difference in crank length, and 5mm is noticeable -- this from personal experience. AND, if a 'natural pedal stroke' was sufficient, then I wouldn't have experienced extreme calf cramps on platforms a few years ago, during a brief switchback to platforms from SPD's. Also, 60 rpm is NOT more efficient than a higher rpm (you specified 100, few do that, though), there's volumes of evidence in knee injuries to affirm that.

Not sure what you're trying to accomplish by linking this, but it's whatever for me.
 
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