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The aerodynamic derivatives governing the crosswind sensitivity of a vehicle are the coefficients of side force and yawing moment. Usually, these derivatives are measured in a wind tunnel under stationary conditions, but driving through a wind gust or a vehicle's wake is a transient process. Therefore, when the behavioral characteristics of a vehicle in a crosswind are calculated with the aid of a mathematical model, the effects of transient aerodynamics should not be neglected. An estimate of these effects is made on a simple model describing the flow past a moving vehicle. At first, side force and yawing moment in stationary conditions are calculated on the slender body theory, which is converted from aircraft aerodynamics to the aerodynamic of ground vehicles. A reasonable agreement with full-scale measurements seems to justify the application of the same theory to the calculation of the transient crosswind-gust factor.

Test series were run on subjects in a motor vehicle simulator and in actual motor vehicles. The test objective was to study the correlations among the subjective evaluation of vehicle handling qualities, test measurements, and various characteristics. Although the data presented in this paper should be considered only a first step, the comparison of simulator results with road test results yielded good data correlation. It was found in both cases that the vehicle response rate (for example, yaw angle velocity) on a sudden steering angle step input exerts much greater influence on the judgment and the performance of the test subject than does, for instance, vehicle damping.