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Thread: BB question

  1. #1
    EastBaySteez
    Reputation: Freerydejunky's Avatar
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    BB question

    My buddy is getting new truvativ cranks for his Yeti AS-x he knows that the bb shell size is 73mm but when he goes to pricepoint to get a 73mm the drop down only says 68. Does that mean that the 68 is compatible with the 73? and how would we find the correct spindle length.... hes gonna be running 2 rings with a 2 ring guide.

    The whole bb area confuses me. Everything else I get and can maintain...

    Thanks for the help
    Gamut
    Team Evil
    Formerly: motormonkeyr6

  2. #2
    mtbr member
    Reputation: Hardtails Are Better's Avatar
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    Which Truvativ cranks are you talking about? That'll help.

    Generally speaking, a 68mm BB does not work in a 73mm shell. If Pricepoint dosn't list a 73mm shell, they're probably out of stock.

  3. #3
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
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    Truvativ cranksets with external BB's are compatible with both 68 and 73 mm shells. Since the crank spindle is a fixed length, the crankset is designed around a 73mm shell, then spacers are used for 68mm shells.

    If your looking at Truvativ ISIS or Howitzer setups...those are also compatible with 68 and 73 mm shells...again, using spacers for the 68mm shell.

    I was just on the Pricepoint page and I don't see any Truvative BB's listed as 68mm only

  4. #4
    Torque me. Make me spin!
    Reputation: BottomBraket's Avatar
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    73 rules

    mtnbiker is right. Any 73 mm BB should work on a 68 mm BB shell as long as the spindle is long enough to provide the desired front chain line. But some 73 mm BBs do not come with the 2.5 mm spacers needed to allow them to fit on a 68 mm BB shell. Make sure your BB comes with these spacers or that you can get them somewhere.

    As I recall, XTR BBs (old school <~2003) come in only one shell width. The XTR BB includes multiple spacers to allow it to work on 68 mm shells, 73 mm shells, and with or without E-Type derailleurs.

    BottomBraket line: If you’re stocking up on bottom brackets, get the 73 mm width because you can get spacers to make them fit on 68 mm shells.

  5. #5
    EastBaySteez
    Reputation: Freerydejunky's Avatar
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    Alright thanks guys. So if he orders a 68 with the right spacers it will work with his 73 as-x frame?
    Gamut
    Team Evil
    Formerly: motormonkeyr6

  6. #6
    Torque me. Make me spin!
    Reputation: BottomBraket's Avatar
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    Clearification!!!!!!!!!!!

    A 73 mm bottom bracket (the housing, bearings, and crank spindle) with spacers will work in a bike frame with a 68 mm bottom bracket shell.

    But a 68 mm bottom bracket (the housing, bearings, and crank spindle) made specifically for a 68 mm bottom bracket shell probably won't work in a bike frame with a 73 mm shell. The drive side (right side) crank arm will be 2.5 mm further from the bike frame, increasing the front chain line. Also, the non-drive side (left side) crank arm may rub against the frame before the crank arm is fully tightened. Eg., the crank spindle will be 2.5 mm further to the right.

    Ask the vendor if the part you want will work with either a 68 mm or a 73 mm bottom bracket shell. Or check with the manufacturer about the compatibility of the specific crank and bottom bracket part number.

    This can be confusing because "bottom bracket" can mean two different things.

    1) bottom bracket- such as Shimano part number BB-M952 (the housing, bearings, and crank spindle that screws into the bike frame

    2) bottom bracket shell - the part of the bicycle frame at the bottom of the down tube and the seat tube that is a cylinder about 1.37 inches in diameter (most modern bikes) cylinder and either is typically 68 or 73 mm wide.
    Last edited by BottomBraket; 10-28-2007 at 08:31 PM.

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