The chatter phenomenon, appearing during high speed cornering maneuvers performed by racing motorcycles, consists of a self-excited vertical oscillation of both the front and rear unsprung masses in the range of frequency between 17 and 22 Hz. The suspensions are not generally able to dampen the above vibrations which start from the rear wheel and suddenly propagate to the front wheel during the corner entry phase, making the vehicle’s handling unpredictable and, ultimately, weakening the overall performance, that is the lap time. It is not clear which is the determining factor causing this phenomenon. Therefore, numerical simulation on a three dimensional, multibody motorcycle model is proposed, taking into account the effects of the major parameters involved, in order to highlight which of them takes part in the vibration. Accurate models for tire and drivetrain have been developed, making it possible to consider tire carcass deformability, chain transmission in both traction and braking states, full drivetrain inertia and anti-hop clutch effect. A critical maneuver experimentally measured on the race track is analyzed. The modal response of the linearized system is evaluated for several configurations extracted from the maneuver. The above maneuver is then simulated with the model, showing the actual vibration uprising. A critical discussion of the possible physical interpretations of the phenomenon is given.

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