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Wind tunnel tests were carried out with a full-scale passenger car over a moving belt. The suspension system of the vehicle was redesigned in such a way that drag and lift forces could be measured whilst the wheels were rolling on the moving ground. The measurements were carried out with an internal balance installed inside the vehicle. Additionally, total-pressure-deficit contour plots were reduced from wake-rake measurements behind the front and rear wheels in order to identify the origin of different bound vortices generated at the wheels. It was found from these tests that rolling wheels have a large aerodynamic influence on passenger cars. They decrease the drag and increase the lift forces in comparison to fixed wheels. This has been established in an absolute and a relative sense by investigating different vehicle configurations.

Different techniques to reduce the aerodynamic drag of cars have been utilized in the past. Although the best results can be achieved with streamlined bodies, these have not generally been acceptable to the buying public. In order to make use of the potential of aerodynamics nevertheless, a procedure called detail optimization has been developed by Volkswagenwerk AG. Representative results achieved with this technique are reported. The step by step drag reduction of several passenger cars is illustrated. The consequent reduction in fuel consumption has been investigated for steady state driving as well as for standarized cycles.

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.