1. A method for estimating a measure of friction between at least one tire on a vehicle and a road surface, the method comprising the steps of: sensing or determining an off-line steering angle, determining a value of the lateral friction between the at least one tire of the vehicle and the road surface by means of a model, in that a functional relationship between the value of the lateral friction and the off-line steering angle is defined in such a way that a non-linear graph of the value of the lateral friction against the off-line steering angle is a function of the initial slope of the value of the lateral friction against the off-line steering angle and of a recursively determined estimated value of the measure of friction, and that the initial slope is independent of the recursively determined estimated value of the measure of friction, sensing a measured vehicle dynamics variable for the vehicle, determining a vehicle dynamics model variable which corresponds to the measured vehicle dynamics variable as a function of the value of the lateral friction, and determining the variance between the measured vehicle dynamics variable and the vehicle dynamics model variable and wherein the recursion when determining the estimated value of the measure of friction includes its modification as a function of the variance which has been determined.