When the pedal is stopped, the chain and the outer sleeve do not rotate, but the rear wheel still drives the core and the jack to rotate forward under the inertial action. At this time, the inner teeth of the flywheel produce relative sliding, which compresses the core into the groove of the core, and the jack compresses the jack spring. When the top of the jack gear slides to the top of the inner gear of the flywheel, the jack spring is compressed to the maximum, and then slides forward slightly, the jack spring bounces onto the tooth root, making a "click" sound. The core rotates faster, and the weight quickly slides on the inner teeth of each flywheel, making a "click" sound. When stepping on the pedal in the reverse direction, the jacket rotates in the reverse direction, which will accelerate the sliding of the kilo and make the "tap" sound more rapid. Multi-stage flywheel is an important part of bicycle transmission.