In this paper, we propose a new approach to compute the domain of variation of the vehicle stable state, described with two essential elements: the longitudinal velocity and the side slip angle at the vehicle centre of gravity. The stable state is determined in respect to risks involving vehicle roll-over and over/under steering. The stable state domain is computed in a guaranteed way, using interval analysis. A validation with simulated data is provided in order to illustrate the principle and the efficiency of the approach.