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I think I understand that it uses a larger (30mm) spindle etc. But is it frame dependent, or do all bb's fit all frames?
Cheers
yes its frame dependent, BB30 uses press fit bearings rather than threaded bearing cups like ht2/square taper etc
Ah, so if my current setup uses hollow tech II its NOT bb30?
Cheers
Correct, unless it's got adapter cups.
There are a ridiculous number of standards around, and few MTBs are actually bb30. Cannondale are the obvious example! Spesh are very close with their OSBB, but it's not quite the same!
Hollowtech is IIRC Shimano's term for hollow forging of cranks, rather than BB (HT I was with an Octalink BB if memory serves).
Shimano uses a 24mm spindle with their external BB's; these should also work with most external BBs except SRAM GXP which has a stepped spindle so the DS & NDS bearings are different diameters (I think). BB86/90 is the same width as a conventional threaded external BB but uses press-fit cups so the cranks are compatible.
BB30 uses a larger spindle and moves the bearings back inside the BB so it's narrower than an external BB setup; various adaptors are available to fit 24mm spindle cranks to a BB30 frame but not the other way round. PF30 is the same width but uses similar bearing cups to BB86 rather than bog-standard industrial bearings, the advantage being that PF30 doesn't need a machined metal BB insert unlike BB30 for carbon frames.
There is an increasing number of BB30/PF30 frames about, mainly XC hardtails (the new Jekyll is about the only long-travel BB30 bike I can think of). Confusingly, the Spesh road OSBB is identical to BB30, but the MTB one isn't.
Does that clear things up any? 😛
Andy
Rotor make a BSA30 BB that allows the use of a BB30 chainset in a standard BB shell.
Vanman
Google is your friend
Nice one for all the info. Not sure I'll ever want to take the bb exam, but think I know what I needed to know.
Good to see, as ever, that bike mfg's are making it easy for us.