Identification of the characteristics of motorcycle and scooter tyres in the presence of large variations in inflation pressure

摘要

Stability and safety of road vehicles are largely affected by tyre properties. Single-track vehicles arecharacterised by weakly damped modes of vibration (weave and wobble) and therefore this phenomenonis even more important. This article focuses on the study of both steady-state and transientproperties of motorcycle and scooter tyres in the presence of very low and very high inflation pressures.The steady-state properties are defined as lateral forces (side-slip and camber forces) and yawtorques (self-aligning and twisting). The transient properties are described in terms of relaxationlength, which represents the distance needed to reach a certain percentage of the steady-state valueof the tyre force. Experimental tests are carried out on a specific rotating disk machine. Three setsof tyres are analysed. Steady-state properties are measured by increasing step by step the values ofcamber and side-slip angles. Transient properties are studied carrying out tests with harmonic sideslipexcitation and measuring the phase lag between the excitation (input) and the tyre force (output).Experimental results show important variations in tyre properties with inflation pressure with generaltrends of all the tested tyres and particular features related to the tyre’s geometry. After the analysisand discussion of experimental results, the measured data are fitted by means of a specific versionof the Magic Formula. The dependence of the Magic Formula’s coefficients on inflation pressure isanalysed and interpolation curves are given.