A nonlinear yaw-roll model for log hauling trucks is developed in this paper. Several nonlinear effects, such as nonlinear tire cornering forces, nonlinear tire aligning moments, and the coupling between the yaw and roll motions, are considered in this model. Using this model, a computer simulation of the directional and roll responses of a logging truck with tractor and pole-trailer configurations is carried out through various maneuvers. Simulated results for the lateral accelerations are compared with those obtained from field tests. Good agreement has been achieved.