slow down said:Depends on manufacturer - Deda is 31.7, but ITM (and most other) is 31.8 OS. I think Cinelli was 26.0 but again ITM is 25.4 (I think)
bonj said:I thought standard was 25.4 oversize 31.8mm?
TheDoctor said:MTB standard is 25.4mm. Road is 26mm. Oversize for road and MTB is 37.7mm or 37.8mm - I forget which way round but they're close enough that it doesn't matter.
Having said that, I've used 25.4 mm bars in a road stem, and I'm currently using drop bars in a 25.4 mm stem, so it seems not to be as critical as all that.