Stability, Control and Steering Responses of Motorcycles

Following on from the author's reviews of the stability and control of motorcycles in 1978 and 1985, the paper treats the earlier material in tutorial fashion and adds more recent information. Fixed and free control properties are compared and it is concluded essential to the operation of a motorcycle that the steering system is free. Motorcycles typically possess lightly damped oscillatory modes and the properties of these modes are discussed. Small perturbations from straight line motion and from cornering equilibrium states are treated. Steering control by handlebar torque and by rider upper body lean torque are compared. The behaviour of the rider as an extension of the structure of the machine and as a controller is also discussed. Theoretical analysis, experimental measurements and general experience are linked as far as possible. More recent years have seen a strong movement towards the use of structurally efficient frames for large motorcycles, in particular, and multibody dynamics software for handling analysis. Theoretical predictions can be extended in ways hardly possible before automated multibody analysis became available. The state of the art is illustrated with a description of a contemporary motorcycle / rider model and some results which are derived from it. Directions for future work are indicated.