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Road Crank Arm Length(3 posts)

Road Crank Arm LengthDY
Jun 5, 2002 12:47 PM
Hi, I was wondering about crank arm length. Are there any easy formulas? I've been to a web site (I don't remember the address right now) that you input all kinds measurments and then you get all kinds of results based on different schools of thought regarding bike fit. I thought that site was actually more confusing.

I am 6'0" tall, I have an inseam of 87cm/34.25 in. If I sit down on a flat surface with my back flat against the wall and my lower legs hanging down (so everything has a 90 deg. angle, back and thighs, thighs and calfs) the distance from the wall to my knee is 61.6cm/24.25in (I guess this measures femur lenght). Does anyone measurments similar to mine? What lenght crank do you use? What crank lenght would you think I would use?

re: Road Crank Arm LengthPMC
Jun 5, 2002 6:07 PM
My legs are pretty close in length to yours and I've tried most everything. I've run 175, 177.5 and 172.5 lenght crank arms. I've come to the conclusion that I really like the shorter 172.5 lenght for pretty much all riding except maybe a day of nothing but climbing.

My spin felt wrong with the 177.5 length.

No formula, just a good number of miles on each size.
Lots of formulasKerry
Jun 6, 2002 5:25 PM
Of course, none of them have any meaning or value, despite the claims of the people pushing the formulas. As it turns out, humans are very adaptable to crank length, and despite all the studies done on crank length, no one has shown a reliable correlation to any physical parameters. Part of this is because performance with any given crank length is due to adaptation. I have the same inseam as you, rode on 170s for about 30 years, switched to 175s, and saw no difference other than 3-5 RPM slower cadence. Same time trial times, same ride times, etc.