Shimano UN91 Bottom Bracket

The UN91 is Shimano’s top of the range XTR level bottom bracket. It is designed to run XTR M900 cranks, hence the limited 107mm and 113mm axle options.

The target market is the pro cyclist who needs the highest level of performance and reliability. It will take years of abuse before the silky smooth sealed cartridge bearings will even consider going notchy.

We really like these and would definitely recommend picking them up second hand. Some of ours are still silky smooth despite having 25 years of use. We can say almost the same about the UN71, which are also available in a much larger range of axle lengths.

Weight-wise, it is very respectable for a sealed unit which will give you far more years of faultless cycling than most super-light equivalents.

Requires a Shimano TL-UN74 or Park BBT-22 tool for installation/removal.

Axle: 107-113mm
Shell: 68mm, 73mm
Thread: English
Colour: Silver
RRP: £24.95
Made: Japan



It appeared from 1993 to 1995 and formed part of the following Mountain and Road groupsets…

M900 – XTR
7403 – Dura Ace

M900 – XTR

M900 – XTR