Shimano Bottom Brackets

The right Shimano bottom bracket depends on two things: your frame's shell and your crank's spindle. Threaded BSA frames with Hollowtech II cranks need a threaded Hollowtech II bottom bracket, press-fit frames need the matching press-fit size, and square taper or Octalink cranks need a cartridge bottom bracket with the correct spindle length and shell width.

A BSA bottom bracket threads into the frame with screw-in cups, while a press-fit bottom bracket presses bearings straight into a smooth shell with no threads. BSA is easy to service with basic tools and rarely creaks, while press-fit allows wider shells and lighter frames but needs a bearing press and a clean, accurate shell to fit well.

Measure across the bottom bracket shell, the short tube at the base of the frame that holds the cranks, from one face to the other. Common sizes are 68 mm for threaded road shells, 73 mm for many threaded mountain bike shells, 86.5 mm for road press-fit and 89.5 or 92 mm for mountain bike press-fit.

Most bottom bracket creaks come from dirt, dry threads or a loose fit rather than failed bearings. Removing, cleaning and greasing the cups or bearing seats, then refitting to the correct torque, often cures it. Check the pedals, chainring bolts and seatpost too, because their creaks often sound as if they come from the bottom bracket.

A Shimano bottom bracket usually lasts several thousand kilometres, and often far longer on dry roads, but riding in rain and mud or washing with a pressure washer shortens its life. Replace it when the cranks feel rough or gritty as they turn, or show side-to-side play once the crank bolts are correctly tightened to the right torque.