Ultegra bottom bracket
Can i use an ultegra bottom bracket with my xt crank? Also, anything wrong with running a roadie cassete on a mtb wheel?
ultegra BB on XT crank: no. The XT crank's spindle is longer, so you need the spacers. If you installed those spacers with a road BB it would't thread far enough into the BB shell.
Road cassette: no problem if it's the right number of speeds and the gears you want. I run a 12/27 on my hardtail, it's been fine for years.
"...I'm afraid that our road and MTB bottom brackets actually are not the same width. Believe it or not, the road ones are wider. So while one may be able to make it work in a pinch with some custom spacers, I wouldn't exactly call them interchangeable.
Multi Service Technical Representative
Shimano American Corporation
As Joules mentioned most Road cassettes should work (except Campagnolo which have a different splined interface and cog spacing) also ideally you would switch to a road derailleur which will follow a shallower arc across the road cogs. However adjusting the B-tension screw to bring your current derailleur's top pulley closer to the cassette should provide adequate shifting.