's Forum Archives - Components

Archive Home >> Components(1 2 3 4 5 6 7 8 9 10 )

Need crank arm length advice...(3 posts)

Need crank arm length advice...baxnbike
May 9, 2003 5:37 AM
Purchased a Masi Gran Corsa 11-02. The bike is 53cm, somewhat small since I'm 5'10" but I have very short legs (31" inseam). I have really enjoyed the bike and I'm about to go over 2000 miles this weekend. The bike comes with full Ultegra parts and a crank length of 175mm. I seem to struggle sometimes when it comes to hammering for extended periods of time. Would a shorter crank of 172.5 or 170 help with my pedaling efficiency at all. Any and all advice for a newbie would be greatly appreciated.
I'd have to say...merckx56
May 9, 2003 6:11 AM
go with the 172.5 cranks. I'm 6'1" and have a 33" inseam and ride 175s, simply because I can turn them over effectively. I rode 172.5s for years and did notice a difference when I moved up and now, when I get on my rain bike, I can tell it has the 172.5 cranks on it. The are several variables involved: leg length, femur length, power output, position..., but if it doesn't feel right, it just doesn't feel right. 170s may be a bit short.
PS- I've got a set of 172.5 D/A cranks, if you wanna trade!

It's personalKerry
May 9, 2003 4:44 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. 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.