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  1. #1
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    What size bottom bracket do i need?

    Hi im new to building bikes and im making a fixie at the moment. I know the bottom bracket has to fit the cranks but i dont know what size bottom bracket i need for my frame. i have an english thread 68mm and spindle length of 125mm. What size bottom bracket do i need to fit the frame. Thanks

  2. #2
    Senior Member gyozadude's Avatar
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    The main issue isn't BB size. You already know it. 68mm English thread. Your problem is knowing what kind of spindle to put in there and how long. That depends on the crankset and the frame dropout spacing. The manufacturer of the crankset usually provides a spindle length spec for a typical rear dropout spacing (e.g. 130mm for modern road bikes, 135 for MTB abd 120mm for track). Sheldon Browns site might also contain some methods for measuring chainline to achieve an approx. length for the spindle. If you plan to mess with axle spacers and shift cogs left or right a few mm, it may be prudent to take a measurement first and follow the formulas posted (e.g. like by Sheldon) and compute spindle length.
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  3. #3
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    Quote Originally Posted by gyozadude View Post
    The main issue isn't BB size. You already know it. 68mm English thread. Your problem is knowing what kind of spindle to put in there and how long. That depends on the crankset and the frame dropout spacing. The manufacturer of the crankset usually provides a spindle length spec for a typical rear dropout spacing (e.g. 130mm for modern road bikes, 135 for MTB abd 120mm for track). Sheldon Browns site might also contain some methods for measuring chainline to achieve an approx. length for the spindle. If you plan to mess with axle spacers and shift cogs left or right a few mm, it may be prudent to take a measurement first and follow the formulas posted (e.g. like by Sheldon) and compute spindle length.
    Yea i was planning to get cranks that require 110mm spindle length and BB thats 110mm. But would it fit my BB shell on my frame?

  4. #4
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by dazchilly View Post
    Yea i was planning to get cranks that require 110mm spindle length and BB thats 110mm. But would it fit my BB shell on my frame?
    As long as the thread and width match your frame it will fit.

  5. #5
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    Quote Originally Posted by JohnDThompson View Post
    As long as the thread and width match your frame it will fit.
    So because my bb shell is 125mm does that mean i need a 125mm bb? or what would be the best length?

  6. #6
    Bianchi Goddess Bianchigirll's Avatar
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    Quote Originally Posted by dazchilly View Post
    So because my bb shell is 125mm does that mean i need a 125mm bb? or what would be the best length?

    A 125mm shell?? how did you measure that?

    BB shells come in three basic sizes since about '85 Italian 36x24 threading and 70mm shell width. English 1.37x24 with a 68mm shell. Also there was (I am not certain this is still inuse) a mmountain bike BB 1.37x24 but a 73mm shell width.

    You need to know whether your bike has an English (most common these days) or Italian. If your bike is Japanese in manufacture (including Tiawain and other Asian countries) odds are pretty good it is english. after say '88/89 even most Italian tubed/manufactured frames came with English BB.

    What you need to do is... figure out what your frame is. Then decide ona crank and buy the bottom bracket that matches the crank.
    Bianchis '87 Sport SX, '90 Proto (2), '91 Boarala 'cross, '93 Project 3, '88 Trofeo, '86 Volpe, '89 Axis, '79 Mixte, '99 Mega Pro XL Ti, '97 Ti Megatube, , '90 something Vento 603,

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  7. #7
    Senior Member surreal's Avatar
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    your bb shell is
    68 millimeters
    from starboard to port

    it accommodates
    all spindles available
    for BSA shells.

    -rob

  8. #8
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    Quote Originally Posted by Bianchigirll View Post
    You need to know whether your bike has an English (most common these days) or Italian.
    The OP already knows the frame is English threaded and has a 68 mm bb shell width. He is confusing spindle length with bb width.

  9. #9
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    Sorry HillRider is right my spindle length is 125mm and i have an english thread of 68mm. Sorry for getting it confused. Sorry dont know what frame it is because i bought it by itsself.

  10. #10
    Bianchi Goddess Bianchigirll's Avatar
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    I read that you had an english but then you asked about the 125 thing and just ran off the rails.

    as I said in my rather lengthy and unneeded post... figure out what crank you are going to use and then buy the BB that goes with the crank. ei if you want to use a Miche Primato Pista crank get the matching Miche Primato Pista BB that goes with it. Origin 8 crank Origin 8 BB
    Bianchis '87 Sport SX, '90 Proto (2), '91 Boarala 'cross, '93 Project 3, '88 Trofeo, '86 Volpe, '89 Axis, '79 Mixte, '99 Mega Pro XL Ti, '97 Ti Megatube, , '90 something Vento 603,

    Others but still loved,; '80 RIGI, '80 Batavus Professional, '87 Cornelo, '86 Bertoni (sold), '09 Motobecane SS, '98 Hetchins M.O., '09 K2 Mainframe, '89 Trek 2000, '?? Jane Doe (still on the drawing board), '90ish Haro Escape

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