Predicting Tyre Behaviour on Different Road Surfaces

Owing to the chosen test procedure, tyre models often represent driving on a sandpaper surface,thereby diminishing the correlation of vehicle simulations with real data from experimentaltests on road surfaces. The discrepancy between tyre measurements obtained on sandpaperversus, e.g., asphalt, is a result of the differences in the local tread rubber/ground frictioncharacteristics. Rubber friction, however, is a complex physical phenomenon for which wehave no complete mathematical theory. Thus, this work took an experimental approach tocapture the tyre friction behaviour in detail. Building on the knowledge obtained from thefriction measurements, a method to transfer tyre shear force characteristics from one surface toanother was developed so that high quality data from indoor testing can be scaled to predicttyre behaviour on real surfaces.The frictional behaviour of tread rubber sliding on sandpaper and asphalt surfaces wasmeasured and corresponding friction master curves were created. The master curves wereintegrated with a simple brush-type tyre model that was extended with a thermal model tosimulate longitudinal and lateral forces. Using tyre force measurements obtained on a flat-trackmachine – which uses a sandpaper surface – the simple brush-model incorporating thesandpaper master curve was parameterised and validated over a wide range of slip conditionsdemonstrating the importance of accurately capturing the friction characteristics. Furthermore,by swapping the sandpaper friction master curve for the asphalt one, the parameterised modelwas shown to accurately predict tyre forces on an asphalt surface by comparing the simulationresults to vehicle-based measurements obtained on the same surface. Hence, the informationcontained within the friction master curve is key to transfer tyre shear forces accurately andreliably from one surface to another.Moreover, the validated model was used to create artificial slip curves on asphalt andsandpaper surfaces. Results show that the investigated tyre consistently produces smaller forceson asphalt than sandpaper; a behaviour that agrees well with published information. Similarly,the model was able to capture known effects of different slip rates and longitudinal velocitieson tyre temperatures and forces very well