A method for managing a vehicle assisted steering system including one assistance function intended to help a driver drive the vehicle and one safety function intended to give assistance function a predetermined ASIL level as defined by the ISO-26262 standard, the assistance function and safety function each make use of a vehicle speed indicator parameter, including a step of estimating a functional speed of the actual longitudinal speed of the vehicle, used by default as the vehicle speed indicator parameter, a step of estimating a speed upper bound, a step of calculating an underestimated speed resulting from the application, to the speed upper bound, of a reduction value derived from a reduction law, and, if the functional speed is lower than the underestimated speed, and a step of switching in which the underestimated speed is substituted for the functional speed as the vehicle speed indicator parameter.