Truvativ Bottom Bracket
There are several different crank bearing systems and standards. The different standards do not allow interchangeability between bearings or cranksets.
Threaded Bottom Bracket
Threaded bottom bracket shells have internal threading. A spindle passes through the frame shell and is held in place by either threaded adaptors (cartridge bearings) or threaded bearing cups (adjustable cup-and-cone type systems).
The BB30 standard was created to allow the use of a crankset with a relatively large 30mm spindle diameter.
BB30 frame shells have no internal threads and a nominal inside diameter of 42mm. Frame shell widths are 68mm for road bikes and 73mm for mountain bikes. A cartridge bearing presses directly into the frame and stops at a snap-ring designed into the frame shell.
The BB30 frame shell will accept non-BB30 cranksets, such as the Shimano Hollowtech II or SRAM GXP, when used with adaptors. These can be simple reducing bushings that slip into the cartridge bearing to reduce the diameter as necessary.
The PF30 standard came after the introduction of the BB30 standard. The shell inside diameter is nominally 46mm. Frame shell width may measure 68mm for road bikes or 73mm for mountain bikes. Cartridge bearings are mounted into either plastic or aluminum adaptors (or assemblies). These are pressed into the frame shell. An outer lip on the adaptor stops against the shell face.
Like the BB30 standard, the PF30 was designed for cranks with a 30mm diameter. Cranksets that are designed for a BB30 will fit the PF30. Similar to the BB30, adaptors are available to permit 24mm spindle diameter cranks to fit frames made in the PF30 standard.
BB86, BB92, or BB121
The BB86, BB92, and BB121 standards use a threadless bore of nominally 41mm in the frame shell.
For road bikes it is 86mm, for mountain bikes it is 92mm, and for “Fat Bikes” it is 121mm. These standards use two-piece cranks with spindle diameters of approximately 24mm.
BB90 or BB95
The BB90 and BB95 standards are Trek Bicycle proprietary standards found on some high-end road and mountain bikes.
The cartridge bearings are not mounted in adaptors as with a BB86/BB92/BB121. Instead, as with an integrated headset, the frame is molded to accept the cartridge bearing as a slip fit. The system uses two-piece cranks with 24mm diameter spindles.
The BBright is a proprietary design by the Cervelo company. This is basically a version of the BB30 or PF30 system.
The bike features a large left side chainstay, so the shell is offset to the left to accommodate this. The frame shell for this design is 79mm, but 45mm of that sticks out to the left, while 34mm sticks out to the right.
To further complicate the BBright system, there are two types. BBright Direct Fit is basically a BB30 type bearing fit, with a shell inside diameter of nominally 42mm. The BBright Press Fit is a PF30 style, with an inside diameter of nominally 46mm.
The 386 EVO is a version of the PF30 system. The frame shell width is nominally 87mm. The inside diameter is 46mm, similar to the PF30. The pressed bearings are the same as PF30 bearings, but the crank must have a longer spindle compatible with a 386 EVO bottom bracket frame shell.
For further information, visit ParkTool's website
Sheldon Brown - Information about BBs and lists
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