On the relationship between tyre cornering stiffness and road surface roughness

Road roughness is usually neglected when studying a tyre’s linear response, as the latter is assumed to depend solely on the tyre’s structural properties. In this article, we present tyre force measurements from three tyres tested on both a flat-track machine and on a real road surface and we demonstrate the lower levels of cornering stiffness observed on asphalt. It is hypothesised that these differences arise from the influence of road roughness on the effective shear stiffness of the tread. On this basis, an enhanced brush-type model is presented to predict the effect of road roughness on cornering stiffness. The model considers three separate stiffness terms: inflation, bending and tread stiffness. The latter is modelled using a finite element model with a rubber–road boundary comprising randomly distributed macro-asperity contact areas, calculated using Persson’s rubber contact theory. A full-factorial Design of Experiment shows a significant dependency of the perceived tread stiffness on road roughness. Finally, the complex moduli of the tread rubber of the three tested tyres and the power spectral density of the road surface are used in the brush model and good correlation is found between the measurement and prediction of the reduced stiffness on asphalt.