The growing popularity of quad bikes in the agricultural area is unfortunately accompanied by an increasing number of accidents and particularly lateral rollovers. Then, the estimation of hazardous situations, whatever the grip conditions and pilot behavior, is a preliminary step in the design of active security devices dedicated to All-Terrain vehicles (ATVs). This paper proposes a rollover metric dedicated to the lateral hazardous situations estimation. It is based on the computation of the Lateral Load Transfer (LLT) obtained, on one hand from a roll projection of the quad bike with its pilot and on the other hand from a backstepping observer dedicated to grip conditions estimation. Capabilities of the proposed observer and metric to estimate hazardous situations on natural ground are demonstrated via both advanced simulations and full scale experiments.