A method for automatically controlling the gearbox of a road vehicle uses a computer using information on displacement speed and transversal acceleration of the vehicle and engine load in order to apply various shifting rules according to the road profile. The gearbox computer applies different gear shifting rules according to the value of a coefficient of activity Kbend depending on the displacement speed of the vehicle (V), the lateral acceleration of the vehicle (Gt) and the derivative thereof in relation to time (dGt/dt).