At least one pair (i) of coefficients (Gi, mui) are determined. These represent the coefficient of sliding (0% = completely gripping, 100% = completely-locked skidding), and the coefficient of friction. The gradient (alphai) of the straight line passing through the origin and Gi, mui is determined. Coefficient B is calculated directly or by regression, starting from an adequate number of pairs, to calculate the value alphao at the origin. alphao is then used to calculate an indication of the longitudinal rigidity of the tread. The gradient alphai is determined directly by calculation as alphai = mui/Gi. It is alternatively determined by adaptive regression. An equation for linear regression is proposed. Further equations are provided for coefficient B, in terms of alpha and G. A mean value for ao is obtained and compared with reference values for the tire under consideration, to assess the degree of tire deterioration. The residual tread thickness is estimated using H = Ho . Rigidity/Rigidityo. A mean value of alphao is found: for a set number of brakings or accelerations, and/or over a predetermined distance.
