1. A system for estimating a maximal grip coefficient μ in the contact area of a tire on a road, comprising: at least one tread sensor adapted to be fitted in a tire tread for measuring at least tangential stresses which the tread experiences locally when the tire rolls on the ground, indicators for certain operating parameters of the tire being chosen from a group consisting of a load of the tire, pressure of the tire, a camber angle of the tire and speed of the tire, and a transmitted torque, a drift angle and lateral thrust Y; a signal processing unit; and means for transmitting to the signal processing unit at least one signal delivered by said at least one tread sensor, wherein the processing unit comprises means for finding in the signal the values corresponding to the at least one tread sensor passing through the contact area of the tire on the ground, means for calculating an instantaneous value of a preselected criterion as a function of a series of values chosen from those relating to the at least one tread sensor passing through the contact area, and means for extracting an estimate of the maximal grip coefficient μ by using the chosen indicators and the instantaneous value of the preselected criterion.