What size bottom bracket do i need?
05-09-12, 01:17 PM
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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 
05-09-12, 01:32 PM
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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.
05-09-12, 02:00 PM
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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.
05-09-12, 02:07 PM
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05-09-12, 02:12 PM
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05-09-12, 03:59 PM
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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.
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05-09-12, 04:03 PM
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05-09-12, 04:30 PM
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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.
05-09-12, 05:43 PM
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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
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
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
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