Investigation of the Influence of Tyre Geometry on the Aerodynamics of Passenger Cars

Artikel i vetenskaplig tidskrift, 2013

It is well known that wheels are responsible for a significant amount of the total aerodynamic drag of passenger vehicles. Tyres, and mostly rims, have been the subject of research in the automotive industry for the past years, but their effect and interaction with each other and with the car exterior is still not completely understood. This paper focuses on the use of CFD to study the effects of tyre geometry (tyre profile and tyre tread) on road vehicle aerodynamics. Whenever possible, results of the numerical computations are compared with experiments. More than sixty configurations were simulated. These simulations combined different tyre profiles, treads, rim designs and spoke orientation on two car types: a sedan and a sports wagon. Two tyre geometries were obtained directly from the tyre manufacturer, while a third geometry was obtained from our database and represents a generic tyre which covers different profiles of a given tyre size. All geometries were deformed based on measured wind tunnel data under a defined load and rotating conditions of 100 kph. Results have shown that the main grooves consistently lead to a decrease of both drag and lift. The edge pattern however, did not show a clear trend for drag and lift with respect to the different configurations studied, although its influence was always more noticeable on the sports wagon. The larger profile of the generic tyre resulted in higher drag and lift values with relation to the tyres obtained from the manufacturer. For a given rim, a drag difference was observed between two tyre geometries with same profile but different tyre tread. These findings lead to the conclusion that tyre profile, as well as tyre pattern, are important to consider. These results were confirmed by wind tunnel tests. In conclusion, the work of aerodynamic optimization of rims cannot be separated from the tyre itself.