A computer model of a tractor-semitrailer is developed which extends that given by Mikulcik in SAE 710045 (Ref. 10 of paper). The extended model allows translation, yaw, roll, and pitch of both tractor and semitrailer. Lateral and fore-and-aft weight transfer is displayed. Wheel dynamics are included, and effects of wheel slip, slip angle, vehicle speed, and tire load are used in the calculation of the tire forces. The vehicle is maneuvered by a simulated driver who specifies the front-wheel steer angle and the brake torques.The ability of the model to accurately describe a real vehicle is studied by using the model to simulate a full-scale experimental test. The model is also used to study two types of proportional braking for a tractor-semitrailer executing a large-radius turn on a wet asphalt track.