Technical FAQ: Shimano road and mountain bottom bracket compatibility

Are Shimano road and MTB external bottom brackets interchangeable?

Feedback on last week’s column regarding Shimano Hollowtech II bottom bracket compatibility.

As the note below from Shimano’s Nick Murdick says, I was wrong about Shimano’s external bearing cups all being the same width. I apologize for misleading any of you into trying it.

Hi Lennard,
As a regular reader of your column, I just read the most recent one on and noticed your answer about our BB compatibility. 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.
-Nick Murdick
Multi Service Technical Representative
Shimano American Corporation