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  1. #1
    mtbr member
    Join Date
    May 2010

    BB size and chainline question (singlespeed)

    I've got a frame with a 68mm shell. Currently chainline is around 50-51mm. I'm switching my M770 cranks to one with a narrower q factor (I think), which is also a square taper (XTR M900). I don't know much about square taper BB's, so just wanted to confirm the sizing.

    If I'm trying to retain the 50-51mm chainline, I would use a 68x113 BB? I would be using the ring on the middle mount. If I'm reading Sheldon Brown's chart right, the 113 spindle lenght should give me a 50mm chainline.

    Sheldon Brown's Bottom Bracket Size Database

    Square taper guru's, please confirm. Thanks.

  2. #2
    mtbr member
    Join Date
    Nov 2011
    A Shimano chart I have says that for a FC-M900, a 107 spindle gives a 47.5 chainline and a 113 spindle gives a 50 chainline.

  3. #3
    mtbr member
    Join Date
    May 2010
    Great. Thanks for the link.

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