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Question about crank arm length(5 posts)

Question about crank arm lengthMariowannabe
May 5, 2003 6:35 PM
I'm 5'10", 32" inseam, ride a 54cm ctc frame which I feel fits me very well. I would say my body is "average" in terms of leg/torso/arm proportions. I ride 150+ miles/week

My riding style: I ride at a pretty good cadence, typically around 100 - 105. 110 when I ride hard. Around 120 things start to break up. I'm training for the etape in France so I'm doing a lot of climbing. When climbing I try to keep the cadence up, but inevitably my cadence drops to 70-85, and some times less, when the hill gets steep (10% +).

My question is: to gain more power (=speed) when climbing, should I consider moving from the 170cm crank I use now, to a 172.5? I ride a 175 on my fixie and that feels OK. In short, would it be advisable to trade some cadence speed for leverage?
re: 170cm crank arm length???cyclopathic
May 6, 2003 5:11 AM
don't get hung up on it. I ride 170 and 175 and I can spin faster with 175. 2.5mm is not gonna make much diff IMHO
re: crank arm lengthFredrico
May 6, 2003 9:41 AM
I'm exactly your size, ride at similar cadences, and have ridden 170mm cranks for too long to consider changing. But many times I've thought about going to 172.5. A friend, slightly taller than me, has been loping up the hills cranking 175s. Claims he gets noticeably more power out of the stroke.
There is no answerKerry
May 6, 2003 4:09 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. That said, an extra 5 mm in crank length may only take away 3-5 rpm of spin, so it is not a large effect. "More power" is only possible if you were somehow not already at the limit when climbing. Your body cannot automatically put out more power just because you change crank length.

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.
Guess I'll error on the conservative side....Mariowannabe
May 6, 2003 4:30 PM
and keep the 170s. Rather than make my knees deal with the added stress from increased leverage, I'll keep working on my spin.

It does seem somewhat ironic that we obsess over seat position, stem length and rise, etc. and that crank length gets such little mention. It seems as its a pretty important part of the machine. Add to that the fact that they are manufactured in 2.5mm increments.... Very expensive part to try different lengths, too.