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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.

Knowledge of the air flow through and within the engine compartments of passenger cars has become more and more important in recent times. Flow visualization has been conducted, but, on the whole, there is a lack of real flow data. Experimental investigations by conventional probes have been, up to now, impossible, due to the highly turbulent and often unsteady nature of the flows resulting from the complexity of the engine compartment geometry. The availability of reliable flow data, would help in solving some critical temperature problems. Furthermore, experimental data could be used as a basis for a numerical approach by CFD codes which could probably help in analysing engine compartment flow in the future. In order to better understand this flow, the Technical Development Center of General Motors Europe has recently carried out an experimental test program, aimed at collecting data on the engine compartment air flow of an Opel Vectra in the Pininfarina wind tunnel.