A tire-suspension-body mathematical model is established based on the twist-beam suspension with time delay being considered.Polygonal wear of tire based on self-excitation theory is discussed.The results show that the polygonal wear is a typical nonlinear self-excited vibration and the frequency range of self-excited vibration fluctuates according to vehicle types and the status of tire worn.The common range of the frequency is from 100 Hz to 400 Hz;polygonal wear of tire(self-excited vibration) occurs when the velocity of a car reaches a given range;the polygonal number of the polygonal wear of tire is equivalent to the ratio of the natural frequency of the system of the selfexcited vibration to the rotational frequency of tire;within the given range,the natural frequencies of tire have a great effect on the system of the self-excited vibration;the twist-beam suspension has little effect on tire polygonal wear.