Friction and camber influences on the static stiffness properties of a racing tyre

Investigation of the stationary load-deflection behaviour of tyres reveals many details of the structure and the rubber to road friction properties. These characteristics are fundamental to the understanding of the behaviour of both the stationary and the rolling tyre. In connection with racing, tyre static stiffness characteristics are of interest as they reflect on the controllability of the vehicle to which they are fitted. In this paper, the construction of a finite element model capable of predicting the static tyre behaviour in great detail is presented. The model is validated against extensive experimental data, including contact pressure distributions and load-deflection characteristics. Static loading tests which involve variations in wheel camber angle and in the friction rules coupling tread rubber with the ground surface, are simulated with the tyre model. The results of the simulations reveal that a friction coefficient of 0.5 is sufficient to prevent sliding in static loading tests for this particular tyre. Lower levels of friction lead to tread sliding and reduced vertical tyre stiffness. Sliding is primarily lateral, leading to narrowing of the contact patch of the tyre. Narrowing also increases the local sidewall curvature which is part of the softening mechanism for both upright and cambered tyres.