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Classification of Bicycle Bottom Brackets

The bottom bracket ("bottombracket" or "BB") refers to the position at the bottom of the bicycle frame where the crank axis of the bicycle is installed. Because this part is also connected to the down tube, seat tube, and 2 rear fork tubes, it is commonly called in Chinese five trues. The bottom bracket is the part that connects the left and right cranks. The main components of the bottom bracket are: the axis of the crank ("spindle" or "axle") directly on the left and right, the bearing ("bearing", that is, the bearing) that helps the axis to rotate, and the necessary protective cover.

Bottom shafts are divided into three categories: Square BB, Splines, and One-piece Bottom Bracket.The types are subdivided as follows:

1. Axis of Square

Square Bottom Brackets are basically used in low-end entry-level vehicles on the market. Bead structure, good waterproof effect, heavy weight, good lubrication and inertia, long service life, and maintenance-free.

2. Spline bottom bracket

Spline bottom brackets are basically used in low-end entry-level vehicles on the market. Eight-key bead gear structure, good waterproof effect, heavy weight, good lubrication and inertia, long service life, and maintenance-free.

3. One-piece bottom bracket

The axis of the bottom bracket is separated from the bearing and directly combined with the crank on one side, and the position of the bearing is moved from the inside of the bottom bracket to both sides. The advantage of this system is that the number of parts is reduced, the weight is reduced, and the structural rigidity is improved. The spacing between the bearings is larger, the burden on the bearings is reduced, and the strength is improved.

The lock-type design can assist in correcting and reducing various problems caused by uneven surface of the frame or bottom bracket tolerances, ensuring that the bearings remain aligned and not shifting, and eliminating the problem of shell and bearing displacement during long-term use of traditional press-in bottom brackets.

The bearing of the lock shaft is closely matched with the housing. The two internal sealing rings can make up the tolerances between various frames and the gap between the housing as much as possible, and can also play a certain waterproof role.