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Recreational Cyclocross and Gravelbiking This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like :The Dirty Kanza". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

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Old 03-27-11, 06:31 AM   #1
w98seeng
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Bottom Bracket Sizing Help Needed.

I moved this. thanks

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Old 03-28-11, 09:10 PM   #2
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No one knows about BB spacing?

Ian
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Old 03-29-11, 12:03 PM   #3
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Have you tried asking the in the Mechanics forum? I don't know a lot about Octalink. Is that one of the standards where the axle length is theoretically paired with the number of chainrings to give you a standard chainline?

In general, given the expected spindle length for a crank, it's easy to calculate the change in chainline that you'd get from a different length bottom bracket. The chainline for a double is the point between the rings, while the chainline for a triple is the location of the middle ring. Generally, you don't want the inner ring to far in, but with a triple, it's good to have the outer ring farther out.

With standard chainlines (43.5/45) and a typical 5 mm spacing between rings, the inner ring is at 41 mm for a double and 40 mm for a triple while the outer ring is at 46 mm for a double and 50 mm for a triple. This is the consensus standard and seems good for most people. Depending on your typical usage, you might be able to get away with some variation.

See also:
http://sheldonbrown.com/chainline.html
http://www.sheldonbrown.com/bbsize.html#shimano
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