Bottom Brackets

Why are there so many bottom bracket standards?

The bottom bracket is a pair of bearings that your crankset spindle rotates in. It is a simple job done by a complicated mess of standards, so more than any other component it requires you to know exactly what your frame and crankset need before buying — nothing like picking up a set of pedals or a saddle.

Which standard does your frame use?

BSA/English threaded (68mm or 73mm shell, 1.375" x 24 TPI threads) is the oldest and most reliable standard — the shell is threaded so the BB screws in, and there is no creaking when properly installed. Shimano, Hope, Chris King and Wheels Manufacturing all make excellent threaded BBs. Press-fit BB92 (also called PF41) has a 41mm bore and an 89.5 or 92mm shell width, with cups pressed into the frame without threads; it is common on mid-range to high-end frames and prone to creaking if tolerances are loose. PF30 uses a 46mm bore and 68mm shell, used by some Cannondale and other brands. T47 is newer, combining press-fit shell dimensions with threads, and is growing in popularity because it solves press-fit creaking problems.

Will it fit your crankset spindle?

The BB must match your crankset's spindle diameter. Shimano Hollowtech II uses a 24mm spindle, SRAM DUB uses 28.99mm, Race Face Cinch uses 30mm, and Hope and others also use 30mm. A DUB BB will not work with a Shimano crankset because the bearing bore is wrong — the most common mistake when buying a bottom bracket, and worth double-checking against the rest of your MTB components.

How do you stop a press-fit BB creaking?

Press-fit BBs are notorious for creaking, and the root cause is frame shell tolerances: if the bore is even slightly oversized, the cups move under load and creak. The fixes are Loctite 641 retaining compound on the cups during installation, or a thread-together BB kit from Wheels Manufacturing or Hope that clamps through the frame like a threaded BB. If your frame has a press-fit shell and you are sick of creaking, a thread-together conversion kit is the permanent fix.

Are the bearings worth replacing?

BB bearings are cheap to replace — most BBs use standard cartridge bearings (6805 or 6806 series) that cost £5-10 per pair. Premium bearings from Enduro, CeramicSpeed and SKF last longer but cost significantly more, and for most riders replacing standard bearings annually is more cost-effective than running ceramic. Hope and Chris King BBs are fully serviceable, so you can replace just the bearings and seals rather than the whole unit.