Vehicle Performance Improvement by Steering a Third Axle

The conventional rear tandem axle of a three-axle vehicle produces a yaw resisting moment that adversely impacts vehicle performance. This work examines the steady-state handling effect of steering the rear axle of a three-axle vehicle in terms of equivalent wheelbase and understeer. It is found that a very simple rear axle steer control strategy improves both the equivalent wheelbase and understeer. The equivalent wheelbase of the rear axle steered vehicle calculated from vehicle performance data equals the intuitively expected kinematic result. Finally, improvement in tire wear by steering the third axle is reported.