Abstract: Influences of the changes of the amplitude and space frequency of road surface roughness on adhesion ability are simulated and analyzed by means of the nonlinear and time varying tyer model made by the author. The conclusions, which adhesion ability of road to the tyre reduces so that braking distance increases while road surface roughness increases, are obtained. Meanwhile, it is seen that the nonlinear and time varying tyre model is useful for the simulation and analysis of braking performances of vehicles on rough road surface because it reflects the real influence of the road surface roughness on tyre.