Is it possible/ advisable to fit a square taper BB on a modern carbon frame?
Depends how modern. If it has a threaded BB shell, you can just drop one straight in. If it's properly modern and has one of the pressed in BBs (BB30, BBRight etc), you'd need some kind of adaptor. Either way, it's hard to see why you'd want to.
Depends how modern. If it has a threaded BB shell, you can just drop one straight in. If it's properly modern and has one of the pressed in BBs (BB30, BBRight etc), you'd need some kind of adaptor. Either way, it's hard to see why you'd want to.