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170 or 172.5(5 posts)

170 or 172.5DeadGame
Mar 4, 2003 3:24 PM
I am 5'10 have a 31 inseam I currently ride 170mm. Would 172.5 throw me off that much. My comfort cadence is around 85-90 if that matters.
It's a muddleKerry
Mar 4, 2003 6:02 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.

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.
re: 170 or 172.5MR_GRUMPY
Mar 4, 2003 8:20 PM
When I went from 172.5 to 175's it took a week to get used to them. It took about two to three weeks to get my same spin back.
Try one of each!brider
Mar 5, 2003 9:58 AM
Okay, just kidding. Kind of.

Chances are, you won't even feel the difference (assuming you adjust seat and handlebar height accordingly). Try both out. See which one gets better results. I know I made some good gains at TTing and climbing when I went from 170s to 175s. Eventually I got to where I could even sprint (or at least as close a facsimile as I can muster) on the 175s. I still use 170s on my track/commuter rig, and at times it feels wierd.
Mar 5, 2003 4:09 PM
As Brider said, there really is not that much difference. But I am within an inch of your measurements and I prefer the 172.5's. I can spin them up to around 175 rpm's in a sprint.