Shimano Hollowtech II bottom brackets

[Chris N]

Are the MTB and road BBs interchangeable for a given BB shell?  And is there any real advantage to speccing one of the higher grade bearing sets over the cheap ones?

[frankly frankie]

The MTB axle is slightly longer than the road axle.  And the MTB bearings are slightly deeper (I think).  So if you fit MTB cranks but retain the road bearings - its doable, its just a matter of adding a spacer or 2.

[Chris N]

But MTB bearings won't fit on road cranks?

[frankly frankie]

My guess - 'probably' OK.  I've only done the opposite.
Most setups I've encountered involve at least a couple of spacers round the BB, so there is that much leeway if you omit some or all of these.  We're only talking say 2mm each side.  Plus, the way it works, if the axle is 'too short' it still all fits together, if 'too long' it doesn't.  Very like a steerer tube and a aheadset - too short is better than too long, and extreme accuracy is not essential.

[Chris N]

In the end I decided to not to try and mix and match - went for a 105 BB to go with the road cranks.  I didn't want to mess around with the chainline as this is for my new fixed build.