[halmagyi]

I have a cannondale optimo 2 and am replacing the truvativ isis crankset
with a shimano FC-R700 compact crankset.

Ive just encountered the problem that the shimano ultegra
bottom bracket I have seems too thick for my frame.

I cant find a good place to learn about these sizing issues,
I thought cyclocross bikes could take road bottom brackets
and cranks...

any ideas?

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[halmagyi]

OK maybe the problem is that Im trying to fit a 70mm shell width bottonm bracket into an
english 68mm hole. does that sound right?

[justinb]

70mm and 68mm are both common bottom bracket shell sizes. 68mm is the most common, IME. You may also want to check the threading on the 70mm bottom bracket cups as they may be italian thread, and your C-dale almost certainly has english threading.

I'd suggest you read more here, (http://sheldonbrown.com/gloss_bo-z.html#bottom) and if you still have questions, cross post in the Mechanics Forum.