Based on previous research, it is found that self-excited vibration of tread play the leading role in polygonal wear of tire, thus, in order to find out the law of vibration, the actual six-component test of tire in car is carried out. As measured six components contribute to the signal are complicated, the six lateral force signal is set as the focus of the object. According to partial coherence analysis, the interference compositions in the signal are excluded, then the frequency of self-excited vibration frequency and simulation result obtined by theoretical calculation are compared to validate the correctness of the theoretical model.