Vehicle stability control system, the system including means for imparting a longitudinal force on the tire and means for calculating the slip parameter G.sup.Opt at each activation of the means for imparting a longitudinal force on the tire in the following manner: as the values of G.sub.i are acquired, calculating the variation in G with respect to time, as long as the variation is above a low threshold, calculating coefficients A.sub.[wet, p] by direct calculation or by an appropriate regression so as to model variation in G with respect to time by a variation curve which is a function of (G.sub.i, A.sub.[wet, p]), as soon as the variation is greater than a high threshold, determining a target slip G.sup.Cwet using at least the last values of A.sub.[wet, p].