Tire ply-steer, conicity and rolling resistance - analytical formulas for accurate assessment of vehicle performance during straight running 2019-01-1237

During straight-ahead running, the longitudinal axis of road vehicles - notably cars - is not parallel to road axis and sometimes a slight steering pull can be felt by the driver. This occurrence is general and is due both to road cross slope (road banking) and to tire characteristics, particularly ply-steer and conicity. In order to describe such a phenomenon, the paper introduces a new and relatively simple analytical model. Despite the linearity of the model, the solution provided is exact, since straight-ahead motion occurs with small angles and both the elastokinematics of suspension system and tire characteristics can be modelled by linearized equations. The validation of the analytical expressions is performed by using an MSC ADAMS full model of a car. By means of the new analytical formulae, the relationship between the tire ply-steer/conicity and the rolling resistance of the vehicle in studied. More precisely, the energy required for straight motion of the vehicle is computed as function of tire ply-steer/conicity and wheel alignment parameters. By means of the validated analytical formulae, it is found that a 2% rolling resistance decrease can be obtained by a proper setting of tire and wheel alignment parameters, which means nearly 1% energy saved to cover NEDC or WLTP missions.