A seven-DOF vehicle model comprising a full car body and four wheel-axle assemblies is used to investigate the influence of active and semiactive suspensions on ride performance. The active control of car body roll, pitch and bounce is based on an optimal control strategy assuming the tire deflection measurements are not available. The frequency analysis shows a significant attenuation in car body modes but a potential increase in wheel motions. Dissipative dampers with solenoid valves are used as the semiactive control mechanism. Simulation results in the time domain indicate that suboptimal values exist in the damping “on” state and an on-off damping control scheme can effectively reduce the car body motions and suspension travels.