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This paper examines the validation process for computer simulations of ground vehicle dynamics. Validation in this context may be defined as the process of gaining confidence that the calculations yield useful insights into the behavior of the simulated vehicle. It is our view that this process requires three separate questions to be addressed: Is the model appropriate for the vehicle and maneuver of interest? Is the simulation based on equations that faithfully replicate the model? Are the input parameters reasonable? This paper addresses each of these questions, mainly from an analytical point of view. The paper then addresses strengths and weaknesses of vehicle testing as part of the validation process.

Vehicle dynamics simulations typically use semi-empirical tire models. The input to these models are normal load, sideslip angle and longitudinal slip, and the output are shear forces, aligning moment, and overturning moment. Since the longitudinal speed is in the denominator of both sideslip angle and longitudinal slip, the calculation of sideslip angle and longitudinal slip at very low longitudinal velocities leads to numerical problems. This has not been a particular stumbling point in the past because vehicle dynamics calculations were largely concerned with high speed analysis. In situations wherein the vehicle was braked to a stop, patchwork techniques sufficed for calculations at low speeds. Now, however, with the advent of serious attention to driving simulators, low speed tire modelling has become more important.