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Crank Lenth????(4 posts)

Crank Lenth????zane
Nov 15, 2002 7:30 PM
What is the best way to determine proper crank length on a road bike?
I don't think there is oneMcAndrus
Nov 16, 2002 6:44 AM
I suggest you do searches on RBR for this topic - you'll find quite a bit. You'll also find no conclusions on what lengths are best for what riders and in what situations.

Let's see if I can summarize. Long legs = long cranks, short = short, and medium = medium. Sprinting = short cranks while climbing = long cranks.

How short is short and how long is long? Check out the discussions and see if you can reach a conclusion because I can't. I just ride 175s because I always have.
18% of femur to floortao
Nov 16, 2002 10:11 AM
I read a paper a couple of months ago that suggested measuring from the floor in bare feet to the top of your femur. The top of it moves back as you lift your leg, several inches below your hip. The author suggested 18 - 18.5% maximizes power output; it stuck with me 'cause my measurement is exactly 100cm and I ride 180mm cranks. Not enough to remember his name though... and you'll find no consensus.
re: Crank Lenth????Kerry
Nov 17, 2002 5:34 PM
It is generally the case that longer cranks make it harder to spin, and high cadence is the best way to minimize knee problems. Every increment of crank length is about 2-3 rpm. Going from 170 to 175 is about 5 rpm. Spinning is more physiologically efficient, all else equal. It is also something you have to practice - you can't say "I can't spin" unless you have spent some serious time working on it, day after day over a season or two.

You will find no high quality data to support any particular crank length as being better than any other. This is true whether or not you correct for leg length, femur length, etc. What little research has been done on crank length suggests that people adapt to different crank lengths and there is no optimum or formula related to body proportion. On the other hand, you will find lots of anecdotal or low quality data to support all kinds of conclusions, and more theories than you can shake a stick at. A rider's response to changes in crank length is 1) highly individual, 2) dependent on riding style and the event (TT, climbing, crits, track racing, etc.), and 3) most important, highly adaptive. This is why it is so hard to study the effect of crank length.

The short answer is: if it feels better and measures faster, do it. If it doesn't feel better but measures faster, maybe you should do it and hope to adapt. And even if it doesn't measure faster, you may adapt and get faster. Simple, eh? NOTE: measures faster means repeat timed distances on different days in different weather, not just "faster on my nightly ride" which can be masked by the effects of weather, fatigue, and the placebo effect of riding on "faster" equipment.