Influence of aerodynamic lift and centre of pressure position in motorcycle stability

Motorcycles are systems with complex dynamic behaviour that can become unstable under certain driving conditions. Avoiding such instabilities from the design stage is not trivial since they depend on various interrelated parameters, one of which is aerodynamics. Aerodynamic forces in a vehicle can be essentially described by its longitudinal (drag) and vertical (lift) components together with its point of application on the vehicle, known as centre of pressure (CoP). Several studies had shown that aerodynamic forces have an influence on stability. Several authors explain that drag influences stability through four mechanisms: dampening lateral motion, and changing weight distribution, tire cornering stiffness, and rake geometry. It is well known that in motorsport performance needs to be enhanced continuously and aerodynamics can be used to this end. Changing the CoP position and the addition of lift force certainly affect the four mechanisms described by (Meijaard, 2006), but their effect on stability had not been described in the literature. Therefore the aim of this research is to extend on (Meijaard, 2006) research, by analysing the influence of CoP position and aerodynamic lift in motorcycle stability in straight line and steady cornering. To this end, we perform a stability analysis on a motorcycle with variable CoP and lift. We consider the CoP ahead, aligned, and behind the motorcycle centre of mass, and in cornering we consider it on both sides of the symmetry plane of the motorcycle to account for rider lateral displacement. The result contributes to the understanding of motorcycle aerodynamics providing new insights into how to use aerodynamics to enhance stability.