[HGR Frucci]

Alright, I'm getting my new Stab Supreme all ready to ride and I decided to replace my 116 XTR BB (M952) with a 118.5 Ultegra (BB6500). I've worked on bikes for probably 5 years and feel confident in my wrenching abilities.

That being said, I remove the XTR BB, pull out the Ultegra BB, go to put it in the frame and...the frickin' cups are BIGGER than the XTR and won't thread into the frame.

I pull the thing out, and hold it up to the XTR and can see the difference in the cup size (OD).

Now feel free to call me a complete tool, but I thought road/mountain/whatever threaded bottom brackets were all the same diameter (except English verus Italian)? Do I have some mutant Ultegra BB or are road BB's actually bigger in diameter?

Hopefully I can send this back for a replacement since I didn't even get it installed.

In my defense - I could have sworn that Darren Stockton told me a couple of years ago that the ITS team was running Dura Ace BB's?? This would support that either road/mountain shell diameters are the same - or - ITS had larger shell diameters in their bikes to accomodate the bb?

Somebody please give me a clue...

 

[buildyourown]

Yes road and MTB are the same. There is english and Italian. The label on the BB should say 1.37 That is the standard major thread diameter for mountian bikes.
You should be able to find an Ultegra or even a 105 that fits as long as your shell width is 68mm

 

[HGR Frucci]

Ok - here's the weird part. The XTR is stamped 1.37 (inch diameter) and the Ultegra is stamped 36 (mm). The TPI on both is the same - 24.

I put the caliper on both and the Ultegra is about 1 mm larger on the thread (I don't have a dial or digital at home). Is this difference between English and Italian? I thought it was just the thread direction?

Man, I have never seen this before. Anyway, looks like I'm making a phone call tomorrow morning.

ADDENDUM:

Just checked out Sheldon Brown's site (awesome). Looks like by his BB table I am the proud owner of an Italian Ultegra BB. His chart shows it as a 36 with 24TPI (as mine is stamped). Looks like that's what my problem is. You were correct on the ISO standard - he has it listed as 1.37 or 1.375 with 24TPI.

Case closed...THANKS!