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  1. #1
    650b me
    Reputation: golden boy's Avatar
    Join Date
    Oct 2008

    BB shell selection

    Let's ignore pressfit shells for this discussion. When would a builder choose a 68mm shell vs a 73mm shell? Is the 68mm shell a more flexible choice, since you can add spacers? Is it all about achieving optimal chainline?

    And a lesser question regarding PMW shells: Anyone using the 1.562" OD shells? Seems overbuilt to me, much like the 44mm head tube. Thus far I've only used the 1.5" OD shells.

  2. #2
    mtbr member
    Join Date
    Mar 2011
    Generally the 68mm is for road and 73mm is for mountain. The thicker bottom brackets will distort less with heat.

  3. #3
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Building a MTB?, though I use the 68mm myself, I do so due to needing to fit both road and MTB cranksets to do what I want to do. The 2.5mm spacers added to each side of the BB shell has not caused me any grief. But it does make sense if you're purposely building for the 1 discipline of MTB to use the 73mm. Simply put, the cups are fully thread supported by a 73mm. The cups are cantilevered in a 68mm, so theoretically weaker. In practice, this may or may not bother you.

    If I don't make an attempt, how will I know if it will work?

  4. #4
    650b me
    Reputation: golden boy's Avatar
    Join Date
    Oct 2008
    Thanks, Eric. I'm with you. In my case, I'm building a dedicated MTB, so there's no reason not to use the 73mm shell. I guess what got me thinking about this was an article in a recent issue of Mountain Flyer. Kent Eriksen built a custom ti hardtail and used a 68mm shell. I just looked at the article again. The customer intended to run it as a singlespeed, so perhaps that explains the use of the narrower shell.

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