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BB question(3 posts)

BB questionbuffedupboy
Sep 24, 2003 9:57 PM
I have an old steel bike that came with a BB of 112mm axle length. I wanna change it to a catridge bb with axle length of 108 (?). Will there be a problem? Assuming the BB shell is compatible?

Regards,
Sean
re: BB questionrussw19
Sep 25, 2003 12:25 AM
Sean, bottom bracket shell width is independent of spindle length. If your bike has an English thread BB than it is either a 68mm or 73mm BB. If it is Italian thread it's a 70mm shell. There are other sizes, but that's the basics of it....

As for spindle length, it is dependent on the crankset that you use. That is how you pick a spindle length. You choose it based on the crank you are using.

What brand and model is your crank? With that info someone may be better suited to answer your question. There is a chance it would work, but it may not. It may cause non-low profile cranks to rub the chainstays. It may also destroy your chainline and make your bike shift like crap.

Russ
re: BB questioneddie m
Sep 25, 2003 4:59 AM
Modern BB axles are symetrical, they extend equally from either side of the BB. Older axles (most loose ball BBs)extended more on the drive side to make room for chainrings. If your old axle is symetrical, the cranks will move inboard 2mm each, and it will probably work, but if your old axle is assymetrical, all of that 4mm difference (and more) will be on the drive side, and it proably won't work. You will need an axle that is a few mm longer than what you have now, and it will move the left side crank away from the centerline of the bike. FWIW, I replaced a 122mm axle with a 114mm, but I had to remove the small chainring for clearance. Go to the sheldonbrown.com and look for a compatibilty chart for axles.