Rear Wheel Steering Dynamics Compared to Front Steering

The lateral dynamics of rear wheel steering vehicles are examined using low order linear mathematical models. The response to rear steer angle inputs differs significantly from the front wheel steering response at low speeds. However, both the transient and steady state responses become less dependent on which wheels are steered as vehicle speed increases. This fact indicates that the unusual fixed control response does not alone cause rear wheel steering vehicles to be unsafe at high speeds. The free control instability unique to rear wheel steering vehicles is analyzed using a torque input model which treats steer angle as a degree of freedom. The cause of this unstable weave mode and the stable front wheel steering weave mode is a ratio of tire slip angle to steer angle in excess of unity during high speed cornering.