Models for off-road vehicles, such as farm equipment and military vehicles, require an off-road tire model in order to properly understand their dynamic behavior on off-road driving surfaces. Extensive literature can be found for on-road tire modeling, but not much can be found for off-road tire modeling. This paper presents an off-road tire model that was developed for use in vehicle handling studies. An on-road, dry asphalt tire model was first developed by performing rolling road force and moment testing. Off-road testing was then performed on dirt and gravel driving surfaces to develop scaling factors that explain how the lateral force behavior of the tire will scale from an on-road to an off-road situation. The tire models were used in vehicle simulation software to simulate vehicle behavior on various driving surfaces. The simulated vehicle response was compared to actual maximum speed before sliding vs. turning radius data for the studied vehicle to assess the tire model.
A direct yaw control algorithm was then developed to enhance vehicle yaw stability on both on- and off-road driving surfaces. The algorithm is based on Lyapunov stability theory and utilizes a differential braking strategy to apply a corrective yaw moment to the vehicle to stabilize its yaw rate. The algorithm was tested in a vehicle simulation environment using the developed tire models. Results show that the proposed algorithm improves vehicle yaw stability and handling on both on- and off-road driving surfaces.