With the move to DynaSys11 for XT M8000, Shimano re-engineered the threaded bottom bracket. Like it's Ultegra level cousin, the outboard bearing cups were downsized because the bearing size was reduced. The new bearings are smaller and reduce rolling resistance without sacrificing durability. You will find the standard internal plastic sleeve that protects the inner bearing seals from dirt and moisture that infiltrates the seat tube. Spacers for use with E-type front derailleurs, 68mm and 73mm bottom bracket shells are included. In addition to the bearing and shell size changes of the MT800, the bearing seals were also upgraded to better protect from water and mud. As with all of Shimano's external bottom bracket cups, proper installation of the cup and crankset is crucial to bearing life. Expect the seals to feel a bit stiff at first, but after a short break-in period, the resistance reduces drastically.

The combination of the Hollowtech crank system and the outboard bearing cups has been a huge success for Shimano. Bottom brackets have been kept affordable, and with proper installation and use, the units have proven quite durable since 2003 when the system was introduced. Remember that on Hollowtech cranksets the crank fixing bolt (star-shaped plastic or alloy bolt that threads into the non-drive side of the crank spindle), is just a bearing pre-load device. This very low-torque bolt takes up slack and pre-loads the bearings. It is not a tightening or retention device. The leading cause of bearing failure in Shimano's external bottom bracket system is over-tightening of this adjustment bolt.

The new MT800 bottom bracket features a 16 notch, 41mm diameter cup size, same as the Ultegra 6800 BB, so you will need a tool such as the Park BBT-59 for proper installation at the listed torque specification. For the money, you can't beat these bottom bracket cups for Shimano Hollow-tech cranks. Yes, there are plenty of upgrades out there, but how much do you have to spend? The BB-MT800 will be smooth and durable, perfectly matching the XT level cranksets for 11 speed, whether running a single, double or a triple.