A method for measuring the grip between a tyre and a road surface wherein there is provided a system comprising one or more optical fibres provided with FBG sensors fixed to the internal surface of the tyre, adapted to record data regarding the state of the tyre, and associated with different reflected wavelength A, said one or more optical fibres having an end part which emerges from the tyre, an optical joint (5, 6) for transmitting the data to an instrumentation within the vehicle, a spectrum analyser for receiving the data, which are sent to a data processing device, adapted for implementing a residual grip identification algorithm and for sending information regarding the residual grip to a device indicating the state of the tyre available for a user of the vehicle and/or to active control systems for driving the vehicle itself, said method comprising the following steps: a - defining the residual grip identification algorithm based on determining three characteristic times t in, t peak, t out which are necessary for monitoring the residual grip status of the tyre, b - sending an interrogation signal from the light source to every FBG sensor, c - generating reflected signals from the FBG sensors which are correlated to a deformation of the FBG sensor, d - generating, by means of a spectrum analyser, a signal containing information regarding A(t) and the digitalization thereof, e - sending the response signal A(t) to the data processing system, f - converting said response signals l(t) into strain signals ε (t) for every FBG sensor which is interrogated, g - the data processing system calculating the three characteristic times: t in by means of the formulae { Dε FBG t Dt = 0 for t < t in Dε FBG t Dt ≠ 0 for t > t in t out by means of the formulae { Dε FBG t Dt ≠ 0 for t < t out Dε FBG t Dt = 0 for t > t out t peak by means of the formulae max t Dε FBG t Dt = Dε FBG t peak Dt h - calculating the residual grip G res by means of the formula: G res = t peak − t in t out − t in a - defining the residual grip identification algorithm based on determining three characteristic times t in, t peak, t out which are necessary for monitoring the residual grip status of the tyre, b - sending an interrogation signal from the light source to every FBG sensor, c - generating reflected signals from the FBG sensors which are correlated to a deformation of the FBG sensor, d - generating, by means of a spectrum analyser, a signal containing information regarding A(t) and the digitalization thereof, e - sending the response signal A(t) to the data processing system, f - converting said response signals l(t) into strain signals ε (t) for every FBG sensor which is interrogated, g - the data processing system calculating the three characteristic times: t in by means of the formulae { Dε FBG t Dt = 0 for t < t in Dε FBG t Dt ≠ 0 for t > t in t out by means of the formulae { Dε FBG t Dt ≠ 0 for t < t out Dε FBG t Dt = 0 for t > t out t peak by means of the formulae max t Dε FBG t Dt = Dε FBG t peak Dt t in by means of the formulae { Dε FBG t Dt = 0 for t < t in Dε FBG t Dt ≠ 0 for t > t in t out by means of the formulae { Dε FBG t Dt ≠ 0 for t < t out Dε FBG t Dt = 0 for t > t out t peak by means of the formulae max t Dε FBG t Dt = Dε FBG t peak Dt h - calculating the residual grip G res by means of the formula: G res = t peak − t in t out − t in