The working principle of its single-stage flywheel: when the pedal is stepped forward, the chain drives the flywheel to rotate forward. At this time, the inner teeth of the flywheel are combined with the kilo. The rotating force of the flywheel is transmitted to the core through the kilo. The core drives the rear axle and rear wheel to rotate, and the bicycle moves forward.

The inner thread of the flywheel is fixed on the right end of the rear axle by screwing, keeping the same plane with the sprocket, and connecting with the sprocket through the chain to form the driving system of the bicycle. It can be divided into single-stage flywheel and multi-stage flywheel in structure.