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crank length ?

Old 11-12-08, 07:57 AM
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sinjun
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crank length ?

is there a formula for deciding crank length ? i am 6 feet tall with a 30 inch inseam, the cranks that came on my bike are 175s, how do i tell if i would do better with a different size without buying them and tring them ?
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Old 11-12-08, 09:19 AM
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For bigger people, bigger crank shafts are good. But only if your BB is high enough for your crank shafts to clear the trail with adequate clearance.
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Old 11-12-08, 09:43 AM
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Sheldon Browns take on it
another article on it
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Old 11-12-08, 02:34 PM
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I usually use this formula:

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Old 11-12-08, 03:04 PM
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Big bike frames are supplied with long cranks- small frames with short cranks.

This works for 99.9% or riders so just borrow a mates bike with 172.5 cranks and see if you can tell the difference. I can't.
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Old 11-12-08, 03:31 PM
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Longer crank = more leverage

But generally smaller people shouldnt use 175 size cranks.
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Old 11-12-08, 07:31 PM
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Originally Posted by sinjun View Post
is there a formula for deciding crank length ? i am 6 feet tall with a 30 inch inseam, the cranks that came on my bike are 175s, how do i tell if i would do better with a different size without buying them and tring them ?
A formula is only a guideline at best. I've tried 165s, 170s, 172.5s, 175s, 177.5s. I use 172.5s on my road bike, 175s on my mountain bikes. I'm 5'10" with a 32" cycling inseam. Formulas don't all agree with what I liked best; my knees vetoed the 177.5s quickly enough on my single speed (but that's partly it was a single speed, too) but were good with the rest of the lengths. Generally shorter arms give you a bit better spin, longer better leverage.

Unfortunately getting a good selection of sizes is getting harder with mountain cranks. There are some shops that have a cycling fitting device where cranklengths can be changed, but I haven't seen one in a while (but don't go to shops all that much either).

edited for stupid sentence based on OP....duh

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Old 11-12-08, 09:24 PM
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A lot of it depends on what kind of riding you're doing. I have a friend thats kind of tall but switched his 4X cranks to 170 to get a little more clearance coming out of corners and it worked out pretty well for him.
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