Patter instability of racing motorcycles in straight braking manoeuvre

The front wheel of a motorcycle during heavy braking in straight motion can lock before reaching the maximum longitudinal braking force, a problem affecting especially performances of road racing motorcycles. This is preceded by a self–excited vibration, referred to as front wheel patter, in the frequency range between 7 and 10 Hz. Aim of the present study is the identification of the actual switching mechanism to instability together with its governing parameters. A minimal model of the front assembly of a motorcycle is proposed, and its stability in equilibrium configurations is studied via eigenvalue analysis. The sensitivity with respect to all its governing parameters is analyzed by means of stability maps and the self–excitation mechanism is explained with the aid of energy balance analysis and phase–diagrams. The results are compared to those existing in the literature and to numerical simulations obtained from a full motorcycle multibody model.