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There is increasing concern about potential differences in aerodynamic behavior measured in steady flow wind tunnel conditions and that which occurs for vehicles on the road. As tools become available for better simulation of on road conditions there is a growing practical value in understanding what range of conditions are important to simulate. Surface pressures measured on the sideglass of a European hatchback vehicle in the MIRA full scale wind tunnel are compared with those measured on-road. The on-road data corresponds to relatively calm, low yaw conditions and the time averaged pressure distributions on-road and in the wind tunnel at zero yaw were very similar. Variations in instantaneous aerodynamic yaw angle produces fluctuations in surface pressures but the sensitivity of instantaneous pressures to yaw angle was lower for the on-road measurements compared with steady state wind tunnel tests.