The front and rear axles of a bicycle are spindles. The central axis of a bicycle, commonly known as the center of heaven, is a rotating axis.
The spindle is used to support the rotating parts, which only bear the bending moment and do not transmit the torque. Some spindles rotate, such as the axle of railway vehicles, while others do not, such as the axle supporting pulley. According to whether the spindle rotates or not, the spindle can be divided into rotating spindle and fixed spindle.
Rotating spindle: when working, the shaft bears bending moment, and the shaft rotates.
Fixed spindle: when working, the shaft bears bending moment, and the shaft is fixed.
According to the function and load of the shaft, it can be divided into spindle, rotating shaft and transmission shaft: wherein, the spindle only bears bending moment and does not transmit torque; the rotating shaft bears bending moment and transmits torque; the transmission shaft only transmits torque but does not bear bending moment, or the bending moment is very small.