Torsional stiffness properties were developed for both a 53-foot box trailer and a 28-foot flatbed control trailer based on experimental measurements. In order to study the effect of torsional stiffness on the dynamics of a heavy truck vehicle dynamics computer model, static maneuvers were conducted comparing different torsional stiffness values to the original rigid vehicle model. Stiffness properties were first developed for a truck tractor model. It was found that the incorporation of a torsional stiffness model had only a minor effect on the overall tractor response for steady-state maneuvers up to 0.4 g lateral acceleration.The effect of torsional stiffness was also studied for the trailer portion of the existing model. By again simulating the vehicle response using varying values of torsional stiffness and comparing these responses with the original rigid model, it was found that the overall effect on vehicle response was minimal for both static and dynamic maneuvers up to 0.5 g lateral acceleration.