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Discussion Starter · #1 ·
Many Shimano and SRAM bottom brackets (both threaded and unthreaded) come with a plastic spacer that goes between the two cups. It seems the only difference between the road and MTB versions of these BBs is the width of this spacer. Is this spacer actually needed or can you install the bottom bracket without it? This would allow me to use a MTB BB on a road frame and vice versa.
 

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Many Shimano and SRAM bottom brackets (both threaded and unthreaded) come with a plastic spacer that goes between the two cups. It seems the only difference between the road and MTB versions of these BBs is the width of this spacer. Is this spacer actually needed or can you install the bottom bracket without it? This would allow me to use a MTB BB on a road frame and vice versa.
I think your talking about the plastic sleeve that is there to keep water from getting into your bottom bracket from inside the frame usually this water I think comes from getting inside the seat tube.
 

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I was going to reply to this a while ago with a dissertation on spacers, but I think VR has the correct assumption about what OP meant.

As with many things, the answer to this question is "it depends".

If you are riding in wet conditions with a frame that has an opening between the seat tube and the BB, then yes you need the sleeve. Without it your bearings would be toast very quickly.

If you never ride in the wet, or if you have a frame where the BB shell is not open to the other tubes then go ahead and leave it off.
 

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Discussion Starter · #4 ·
Aren't the bearings sealed? How would water from the inside be different from getting sprayed from the outside?
 
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