According to the nonlinear theory, the bifurcation characteristics of front wheel selfexcited shimmy of some motor vehicle with nonindependent suspension were studied. Computer programs were carried out to calculate the range of selfexcited shimmy speed of the motor vehicle with MATLAB when Hopf bifurcation took place. Various bifurcation diagrams indicating the relationship between angle amplitudes of right tire and vehicle speed were presented. And the influences of different parameters on selfexcited shimmy were analyzed. Numerical simulation results have indicated that the increase and decrease of the structural parameters of steering mechanism and tire parameters can restrain the selfexcited shimmy. With the change of some parameters, the vehicle speeds relating to the tire maximum angle amplitude of the selfexcited shimmy change correspondingly. The steering stiffness, tire cornering stiffness and pneumatic trail show greater impact on the amplitude of selfexcited shimmy.