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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 05-15-08, 03:56 PM   #1
bklein
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How to decide on crank length?

I'm in the process of ordering new cranks, chain, BB, headset and front break for frame that was just painted. Paint looks HOT out in the sun. The bike's last previous life included life included fixed gear with 170mm cranks and 27" wheels that I'm keeping for at least a few months. I don't recall ever hitting the ground with these cranks, but I also never really rode it all that hard.
Is there a calculation or specific frame dimensions for deciding correct crank length?
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Old 05-15-08, 04:07 PM   #2
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http://www.velonews.com/article/5257
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Old 05-15-08, 04:09 PM   #3
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Optimal crank length will depend on the length of your legs. There are lots of different formulas, but googling "crank length femur" will give you a ton of answers.

If 170 worked for you before without problems, why not stick with it?
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Old 05-15-08, 04:23 PM   #4
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a) how tall are you?

b) unless your height is pretty uncommon, 170 will be perfectly fine, and if you're not riding that hard, you're probably not going to notice a huge difference between 170 'n 165 length cranks.

that being said, i just ordered a set of cranks in 167.5. i have a really hard time getting a lot of torque out of 165s without getting out of the saddle more often than i'd like to. *theoretically* the slightly longer crank will allow me more torque without sacrificing as much control.

mind you, these are for my track only bike.

...that i won't be racing for the next 4 to 6 weeks minimum.



i'm rambling.
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Old 05-15-08, 04:39 PM   #5
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i ride 175's with soma track pedals and have had no clearance issues. i like the longer cranks for the 9 miles of uphill on my way home from school. im 6'2 wit ha 62 frame too so it works out pretty well for me. 170s are prolly good if your a more normal size.
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Old 05-15-08, 04:43 PM   #6
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The only real way to decide is to try different length cranks and see which you prefer. Don't believe any recommendations you read - it's too personal. Some people don't notice 5mm or more difference, while others notice 2.5mm or less. 170mm is the easiest and cheapest to get...

FWIW, I've tried 165, 170, 172.5, 175, 178 and 180mm and decided that 172.5mm was the size for me on all bikes except the fixed wheel. This has 170mm to make spinning down hills less traumatic - it felt like my legs were about to be torn off with 172.5mm. I couldn't climb comfortably with 165mm, and never hit the pedals with 170mm anyway, so it was an easy choice for me to make. If you have much longer or shorter legs, or are used to longer cranks from riding a MTB all the time your most comfortable length may well differ.
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Old 05-15-08, 04:54 PM   #7
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Track frames have higher bb's than road frames; if you've got a road conversion you may want to consider going to a smaller crank arm. But if you've had no troubles, don't switch.

I had 175's on my road bike, switched to 170's and could really tell a difference in my cadence and no difference in my climbing ability. I'm 5'8" with 30" pbh, if that helps. I did have a nasty pedal strike on my fixie with 170's; launched the bike into the air as the pedal hit the ground while I was in a high speed turn. Almost lost it but survived unscathed. Not a fun thing. My next fixie build up will have 165's.
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Old 05-15-08, 06:21 PM   #8
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Quote:
Originally Posted by sp00ki View Post
Ok, by calculation I need 165-167.5mm cranks. But aren't these calcs for road bikes used on the road?
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Old 05-15-08, 07:19 PM   #9
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Originally Posted by bklein View Post
Ok, by calculation I need 165-167.5mm cranks. But aren't these calcs for road bikes used on the road?
Don't you have a (fixed) road bike that you're going to use on the road?

165s will work great for you and should be easy to find.
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Old 05-15-08, 08:31 PM   #10
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I ride several bikes having 170 and 175 cranks.

The 170's spin faster and have better cornering clearance, and the 175's require less effort but don't spin as fast.

I have given some thought to trying 165's in order to spin faster.

Some years ago I researched crank length in relation to body proportions, and I found little agreement amongst the "experts."
Therefore, I just pick between spinning faster or climbing more easily.

My 175 crank bike has the highest bottom bracket shell of all my bikes, and so cornering clearance has not presented an issue.

Just for grins, try leaning your bike over when not riding it and see how far it must lean before the pedal contacts the ground.
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