Crank spin question
07-19-11, 10:07 PM
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Crank spin question
Last night I was doing some bike maintenance on my daughter's BMX bike and my Giant. With the chain on I noticed that the crank on the bmx would spin around several times with just one big backwards throw, while the crank on my bike would only spin about 1 1/2 times around. Is this normal?
Last edited by pgjackson; 07-19-11 at 10:26 PM.
07-19-11, 10:26 PM
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Friction caused by the RD and its subsequent pulleys. BMX cranks only have the rear sprocket/cog to work with. I can't back that up, I just pulled that out of my ass 
07-20-11, 10:30 AM
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On my roadbike with Campy group I can give cranks a light spin and they'll spin several times - the bb feels like it has no friction at all. I think it should spin more freely than what you described.
07-20-11, 10:47 AM
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Yup. Spins smooth as can be. I have found that Shimano FSA etc don't spin as friction-free so it may depend on bb and maintenance level of bb.
07-20-11, 11:11 AM
#11
Throw the stick!!!!
I have found that the freewheel can have a huge effect on how the crankset spins. With one wheel mine only spins once or twice, with a different wheel it will spin several times. Pretty simple to decide if it is the freewheel limiting the spin or the bb. Just take the chain off. 
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