XTR(FC-M900) crankset: compatible bb?

Discussion in 'Cycling Equipment' started by JBF, May 19, 2004.

  1. JBF

    JBF Guest

    I've purchased a first generation XTR crankset(FC-M900). The Shimano
    Small Parts Catalog states the use of Model BB-UN90 (113mm or
    107mm)only. I believe I can use the current BB-UN72 in 113mm spindle
    length to maintain the 50mm chainline.
    It's a decade old catalog & I don't believe they made another
    compatible bb in a 113mm length at that time.If anyone can offer
    insight I'd appreciate it.

    Thanks,
    JB
     
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  2. rocketman58

    rocketman58 Guest

    The current UN73 BB in 107mm will work perfect. That is what I am
    using right now. I have used the older UN72 as well. The 107mm x 68
    provides the correct chain line for my Ti hardtail. I can not imagine
    using a 113mm (maybe a 110mm for certain frames with some clearance
    issues).

    The crank provides a pretty wide "Q" factor. With a 113mm wide BB,
    your feet would be pretty far apart, and it would not provide the
    correct chainline in my experience. I tried a 115mm BB for use with a
    4th inner chainring. While this did work, the "Q" was so wide, I
    found it uncomfortable (and I have pretty wide hips).

    When I used this crank on a roadbike, I used a 103mm Dura-Ace BB. It
    worked perfect for the road bikes 130mm rear wheel spacing.

    Did I mention that in my opinion, this is the best crank ever made?


    "Thumbie", XTR-M900 crank with 46,34,20 chainrings.



    [email protected] (JBF) wrote in message news:<[email protected]>...
    > I've purchased a first generation XTR crankset(FC-M900). The Shimano
    > Small Parts Catalog states the use of Model BB-UN90 (113mm or
    > 107mm)only. I believe I can use the current BB-UN72 in 113mm spindle
    > length to maintain the 50mm chainline.
    > It's a decade old catalog & I don't believe they made another
    > compatible bb in a 113mm length at that time.If anyone can offer
    > insight I'd appreciate it.
    >
    > Thanks,
    > JB
     
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