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  1. #1
    Senior Member w98seeng's Avatar
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    Bottom Bracket Sizing Help Needed.

    I moved this. thanks
    Last edited by w98seeng; 03-29-11 at 01:52 PM.

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    Senior Member w98seeng's Avatar
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    No one knows about BB spacing?

    Ian

  3. #3
    Team Water Andy_K's Avatar
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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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