Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Crank spin question

Old 07-19-11, 10:07 PM
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pgjackson
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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.
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Old 07-19-11, 10:26 PM
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tagaproject6
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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
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Old 07-19-11, 11:42 PM
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It's correct, though.
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Old 07-20-11, 09:25 AM
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That makes sense. Thanks.
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Old 07-20-11, 09:35 AM
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Originally Posted by pgjackson View Post
one big backwards throw, ?
?

Originally Posted by tagaproject6 View Post
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
Tis the BF way.
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Old 07-20-11, 09:36 AM
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Originally Posted by pgjackson View Post
one big backwards throw, ?
?

Originally Posted by tagaproject6 View Post
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
Tis the BF way.
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Old 07-20-11, 10:00 AM
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Originally Posted by rollin View Post
?


Meaning, spin the crank backwards forcefully.
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Old 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.
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Old 07-20-11, 10:35 AM
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Originally Posted by markwebb View Post
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.
Is that with the chain on?
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Old 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.
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Old 07-20-11, 11:11 AM
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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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Old 07-20-11, 11:58 AM
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Originally Posted by tagaproject6 View Post
I can't back that up, I just pulled that out of my ass
This goes without saying...you don't actually need to type it.
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