Question: I’m a 6-foot-tall big-gear masher with a 34-inch inseam. I use 175-mm crankarms. But I wonder if shorter would be better. Here’s my theory: Because the hub travels slower (a shorter distance) than the tire (which goes a longer distance) it seems logical to go to a shorter crank. Higher gear, slower cadence = shorter cranks. What do you think? — Lou B.
Coach Fred Matheny Replies: I think I should have learned more physics and geometry. You’re way ahead of me with all this talk of circles and distances. I grew up near Cleveland and thought Euclid was a downtown street. And I guess I was more of a square.
In any event, I’m not so sure that crank length is a function of geometry (or physics) so much as it is of physiology.
Muscle fiber type and other physical factors seem to play the biggest role in the crank length that works best for a given rider.
Cyclists with predominantly fast-twitch fibers often spin faster and prefer shorter crankarms than riders whose legs are filled with slow-twitch fibers that like to push larger gears at a lower cadence. For that style of pedaling, longer cranks provide more leverage.
Injury history plays a role, too. Riders who have suffered knee problems often do better with shorter cranks. With a smaller crank circle, knees don’t bend quite as much at the top of the stroke or reach as far at the bottom.
Coach Fred Matheny is an RBR co-founder who has four decades of road cycling and coaching experience. He has written 14 eBooks and eArticles on cycling training, available in RBR’s eBookstore at Coach Fred Matheny, including the classic Complete Book of Road Bike Training, which includes 4 eBooks comprising 250 pages of timeless, detailed advice and training plans. The Complete Book is one of the many perks of an RBR Premium Membership. Click to read Fred’s full bio.