Threaded bottom brackets remain the go-to choice for frames that support them, and there are good reasons for that reputation. The BB-MT801 threads into standard BSA shells, which means you can remove and reinstall it without special presses or the alignment concerns that come with press-fit systems. If a bearing eventually wears out or you need to chase the threads, the process stays straightforward. Shimano built the BB-MT801 with the same bearing and seal technology found in the XT press-fit version, so you get the friction reduction and contamination resistance without giving up the serviceability that threaded systems offer.

The bearing updates matter more than they might appear on paper. Shimano reduced the ball size compared to previous XT bottom brackets, which drops both rotating mass and internal friction. Bottom brackets spin constantly while you pedal, and even small efficiency gains compound across a ride. The sealed cartridge design keeps water and trail debris from reaching the bearing surfaces, and the updated seal system borrows directly from XTR. That seal improvement shows up most during wet and muddy conditions where contamination typically accelerates bearing wear.

Shell width compatibility covers 68mm and 73mm frames using BSA threading with a 34.8mm shell diameter. The kit includes three 2.5mm spacers to handle the width difference and dial in the chainline. For 73mm shells, you'll use all three spacers on the drive side. For 68mm shells, the spacer arrangement depends on your crankset and chainline requirements. The 24mm spindle interface works with Hollowtech II cranksets from Shimano, including XT and SLX, plus compatible cranks from other manufacturers that use the same spindle diameter.... Read More