Optimal tyre inflation pressures for urban buses

Abstract

The distribution of passengers using city buses suggested that buses generally carry very light loads over appreciable periods of operation. The influences of variations in tyre pressures with varying passengers load on vertical acceleration and dynamic tyre load responses are investigated. A non-linear three-dimensional model of an urban bus is employed to identify optimal tyre pressures corresponding to different passenger loads, while ensuring comparable magnitudes of static tyre deflections to minimise the risk of heat build up under lower pressures. A road test program was subsequently undertaken on selected routes and different passenger loads, to measure body acceleration as a direct measure of ride quality, and axle acceleration as indirect measures of tyre loads transmitted to the pavement. The results showed that the use of constant recommended tyre pressures causes significantly higher sprung and unsprung mass accelerations under lighter loads. Both the simulation results and the measured data revealed considerable reductions in bus body acceleration and dynamic tyre loads transmitted to the pavement with optimal tyre pressures, for the passenger loads considered. The results suggest that the implementation of a load-dependent central tyre inflation system would be beneficial for enhancement of passenger- and road-friendliness of urban buses.