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bottom bracet help (please)

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bottom bracet help (please)

Old 07-23-07, 06:36 AM
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bottom bracet help (please)

I need help with a BB length question.

OK I know I have a italian threaded 70mm BB from an older CX Pinerallo bike. I undertand it is conventional threaded ob BOTH sides. Right Tight Left Loose on both sides.

Here is my question - Why are there so many different lengths when it comes to overall width? Some are 109mm some are 113mm etc. What do these relate to? Does it deal with rear dropout spacing and chainline type of stuff?

The current cone and cup bb is about 113mm. If I am changing out the crank and BB, do I need to worry about this 113mm measurement? or should I stick with the 113mm and then get a crank from there or can I pretty much go with any length if I a changing the BB and Crank? Thanks.
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Old 07-23-07, 06:39 AM
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It depends on the crank you get. Find the crank you want, and usually, it will specify the correct spindle length for it. Too short of a spindle and youll hit the crank arms on the chainstays, too long and your chainline will be off
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Old 07-23-07, 06:48 AM
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Factors affecting drive-side axle length:
  • crank dish and arm flare (I'm sure there's a technical term for these)
  • number of chainrings
  • chainstay flare (partly dictated by frame geometry and tire size)
  • rear chainline
Not much point in asking why. You need what you need. If you're using the same crank, you need the same drive-side axle length. Don't confuse this with overall axle length. Axles need not be symmetrical.
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