Roller rig tests were adopted to illustrate two typical types of Hopf bifurcations existing in the railway vehicles. In order to investigate the influence of the vehicles' parameters on the features of Hopf bifurcation, a suspended single wheel set model was formulated. In this model, the lateral and yaw motions of the wheel set were taken into account; Restoring forces between the flange and rail were considered as a smooth function through polynomial fitting; Wheel tread profile was assumed to be conical; Suspension elements and creep forces were considered to be linear properties. The continuation method was utilized to study the features of Hopf bifurcation of the wheel set model. Based on the suspended single wheel set model the effect of the primary suspension, the equivalent conicity of the wheel tread, the mass and spin moment of inertia of the wheel set, and the axle loads on the characteristics of Hopf bifurcation were investigated. Furthermore, the combined effect of parameters was analyzed, and the coupling regions between the parameters were found. In the coupling region, the characteristics of Hopf bifurcation are very sensitive to the variation of the parameters. Therefore, in order to avoid the abrupt change of features of Hopf bifurcation, the coupling region of parameters should be taken into account in the design stage of railway vehicles.