Pressed-in bottom bracket smoothness.
It's easy to overlook the humble bottom bracket in the quest for the most efficient, drag-free riding experience, as this component usually does its job without putting up much of a commotion. Thankfully, though, Shimano knows how integral this component is to your drivetrain, which why it spends considerable time making certain that it uses only the best, silky-smooth bearings, advanced sealing, and high manufacturing tolerances.
Such is the case with its new Ultegra SM-BB72-41B PressFit Bottom Bracket design. Where a typical road bike has a 68 or 70mm bottom bracket shell width, a BB86-equipped frame has a shell that measures 86.5mm wide. A BB86 shell lacks internal threads and has a 41mm inside diameter.
This SM-BB72-41B PressFit bottom bracket is made to press right into your frame. It will mate your Shimano HollowTech crankset to any frame equipped with a BB86 bottom bracket shell. This bottom bracket also comes with two steel cartridge bearings that are pressed into composite cups. The cups increase the outside diameter of the assembly to 41mm in order to match the frame's bottom bracket shell. There's a 1.75mm thick outer-lip that provides a positive stop for the cups when you press them into place.
The Shimano Ultegra SM-BB72-41B PressFit Bottom Bracket is available in one size. The assembly weighs in at around 63 grams.