Bicycle Crank Length: Why it Matters

There are certainly some constraints to crank lengths - such as toe-overlap and BB height - but on the short side of things it makes so much more sense from a design and ergonomic standpoint to use shorter cranks. For example, I am 5'2" and own a Georgena Terry bicycle with a 24" front wheel, which is intended to reduce toe-clip overlap and the top tube size while keeping the same gear-raties by having a 700c rear wheel. I have been having knee problems for quite some time because of riding bikes that fit me poorly. I recently replaced my 165mm cranks on the Terry with 145mm cranks, and they are much more comfortable and I would think most people that observed me ride would say that I look like a more normal cyclist (without my knees coming up to my chest). It would take at least one major commercial bike mfr to begin using a wider crank range for people to get it. As the author implied, offering crank lengths in a small range of varying increments may appear to accommodate a wider range of legs, but really, it just allows people in a normal size range to better optimize their efficiency.

Of course in a perfect world but you have to consider that crank length is sort of intertwined with BB height, which is in turn related to wheel size. So no argument, in a perfect world, we would all be riding custom serottas with tailored BB heights and inseam appropriate cranks, but none of us would have bikes without mass production, so there are caveats.

Check this article out for a little scientific method on cranks and pedaling efficiency:

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf

It seems to confirm what we intuitively know to be true but lack the confidence to believe.

I agree with you that this is a very important topic and something that appears to not have enough research surrounding it. I have done my own studies and I have come to many conclusions. One being that the experiment is very complicated to get correct results for, for the simple reason that the athlete will adapt to the crank length he is using. For example, even if a 170 is the ideal length for him, he could train more on the 175mm lengths and the result would be hight wattage output on the longer crank despite being too long. My theory is that the researchers must do a study that spans over time in order to test the athlete after they acclimate and train with each arm length. I suppose that the researches could force the athlete to spend equal time training with each crank to keep from having a 'training' bias, that I mention. Your comments are welcome.

awesome