Bicycle Mechanics - Hopefully simple bottom bracket question

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Slacker
04-18-05, 10:31 PM
I just bought an older Trek (lugged steel) from a garage sale, and it needs some major work. It currently has a triple chainring, but two of the chainrings are missing some teeth and the bottom bracket has a nasty wobble. I thought I'd just install a double crankset and buy a new bottom bracket.

What length BB spindle do I need for a double crankset? This is something I haven't had enough experience with to fully understand -- is this something that's regulated, or is it different from bike to bike? Can I always use x-length with doubles and x-length with triples? Is it something specified by the bike manufacturer, or the crank manufacturer?

Thanks guys!

531Aussie
04-18-05, 10:47 PM
It's usually specified by the crank manufacturer. So, once you decide what cranks you want, this will determine the type and width of the bottom bracket.

Having said that, there's a slight chance the Trek could have not have the standard, English bottom bracket shell.
ofofhy
04-19-05, 05:58 AM
Sheldon Brown has a darn informative site.

http://sheldonbrown.com/bbsize.html

sydney
04-19-05, 06:20 AM
Having said that, there's a slight chance the Trek could have not have the standard, English bottom bracket shell.There is no chance of that so why muddy the water.
FunkyTang
10-13-05, 07:15 PM
Trek uses English bottom brackets?
DannoXYZ
10-13-05, 09:50 PM
If he bought the bike in the U.S. most likely it's an English BB...


I just bought an older Trek (lugged steel) from a garage sale, and it needs some major work. It currently has a triple chainring, but two of the chainrings are missing some teeth and the bottom bracket has a nasty wobble. I thought I'd just install a double crankset and buy a new bottom bracket.

What length BB spindle do I need for a double crankset? This is something I haven't had enough experience with to fully understand -- is this something that's regulated, or is it different from bike to bike? Can I always use x-length with doubles and x-length with triples? Is it something specified by the bike manufacturer, or the crank manufacturer?

Thanks guys!
Decide on a double-crankset first, then pick out the matching BB. The manual will give you a range of BB spindle-lengths to work with, anywhere from 107-125mm+ lengths. You then match up the crankset to the rear-dropout widths on your particular bike, 126mm for 6/7-speeds up to the current 135mm. Pick the spindle-length that works for your particular bike. :)