Singlespeed & Fixed Gear - Crank length and geometry

I was just wondering how much crank length effects the geometry of the bike. Say, if I go from 170 to 165 mm cranks do I just move the seat up a bit? What are the pluses and minuses of going a bit shorter? Thanks.

shut the **** up

Actually, go ride it first, you may not notice the difference. If you do, just move the seat up a touch, it wont take much, 5mm is not much. The only thing you gain is a bit more pedal clearance while turning, and a touch less leverage while climbing out of the saddle. Shorter cranks are more suited to spinners than mashers. 5mm one way or the other is not effect the geometry of the bike in a noticable amount.

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I was just wondering how much crank length effects the geometry of the bike. Say, if I go from 170 to 165 mm cranks do I just move the seat up a bit? What are the pluses and minuses of going a bit shorter? Thanks.


yep, just raise the seat. buy cranks based on how long your legs are. im about 5'11" and much prefer 170's.

crank length has nothing to do with geometry, and everything to do with proper bike fit.

...and everything to do with proper bike fit.

totally. i'm a 5'5" shorty and have 165mm cranks on one of my bikes - it feels way better than the 170mm cranks i have on the other.

It's 5mm, which is half a centimeter, which is not much at all. You probably wouldn't notice anything, but theoretically there will be a small effect on your gain ratio (as you go to shorter cranks, it will become harder to push a given gear, but there will be less distance traveled through the entire stroke). As others have noted, what length you want is dependent on your height, your leg inseam/length of femur, and what kind of ratio you're running (spinning or mashing), though this is also problematic as different 'experts' will tell you different things. Shorter cranks will also reduce your chance of pedal strike, albeit only slightly.

I have 170mm cranks on my street Pista and 175mm cranks on my Surly Karate Monkey Ice Bike.

I set the respective saddles the same length from the pedals.

I expected to feel some difference in spin, with 170's spinning faster than 175's, but I experienced exactly the opposite.

I suspect it has something to do with the 175's matching my body's geometry a little better.

I enjoy riding both bikes for their differences.