Experimental and numerical analysis of rider motion in weave conditions

Abstract

Motorcycle dynamics is characterised by the presence of modes of vibration that may become unstable and lead to dangerous conditions. In particular, the weave mode shows large yaw and roll oscillations of the rear frame and out of phase oscillations of the front frame about the steer axis. The presence of the rider influences the modes of vibration, since the mass, stiffness and damping of limbs modify the dynamic properties of the system; moreover, at low frequency the rider can control oscillations. There are few experimental results dealing with the response of the rider in the presence of large oscillations of the motorcycle. This lack is due to the difficulty of carrying out measurements on the road and of reproducing the phenomena in the laboratory. This paper deals with a research programme aimed at measuring the oscillations of the rider's body on a running motorcycle in the presence of weave. First, testing equipment is presented. It includes a special measurement device that is able to measure the relative motion between the rider and the motorcycle. Then the road tests carried out at increasing speeds (from 160 to 210 km/h) are described and discussed. Best-fitting methods are used for identifying the main features of measured vibrations in terms of natural frequencies, damping ratios and modal shapes. The last section deals with the comparison between measured and simulated response of the motorcycle–rider system in weave conditions; good agreement was found.