On the influence of ride height changes on the aerodynamic performance of wheel designs

Abstract

On the road a passenger car's ride height is elevated both by the radial expansion of the tires due to centrifugal forces and aerodynamic lift. Wheel size and design influence these forces and therefore may affect aerodynamic drag more than predicted using fixed-ride-height tools. In this study, on-road ride height and surface pressure measurements for different wheel designs on a BMW 3 Series sedan are compared to wind tunnel tests and numerical simulations. Compared to still conditions, the vehicle is elevated by 5 to 7 mm when driving at 140 kph. This ride height change increases drag by 4 counts in the wind tunnel. However, the drag differences between the specific wheel designs are only altered marginally. Using CFD, areas sensitive to wheel designs are identified and analyzed. Furthermore, lift differences between the wheels are explained by the vehicle's pressure distribution.