Rationale is presented for improved off-road mobility performance prediction capability through mathematical modeling of the vehicle-terrain system. A hybrid model is described which combines the advantages of real time analog computation for vehicle dynamics with versatile digital function generation for terrain. The vehicle, either wheeled or tracked, is modeled as a rigid body with 5 deg of hull freedom and with a realistic suspension system (appropriate for the running gear) and power train. Model results are presented for a representative wheeled vehicle traversing off-road terrain. Also discussed are extensions of model capability to predict performance of advanced vehicle concepts, and to introduce the driver “into the loop” via a driving simulator which provides visual and motion cues.