1. A system for estimating the maximal grip coefficient t 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 the tangential stresses which the tread experiences locally when the tire rolls on the ground; a signal processing unit; and means for transmitting to the signal processing unit at least one signal delivered by said tread sensor, wherein the processing unit comprises means for finding in the signal the values corresponding to the 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 sensor passing through the contact area, and means for extracting an estimate of the maximal grip coefficient μ by using the instantaneous value.