Heavy vehicles with high centres of gravity are prone to rollover accidents. For a given height and width, stability is affected by suspension design. In articulated vehicles, the matching of the tractor and trailer suspensions, as well as the degree of coupling between tractor and trailer, affects the stability of the combination. A number of loaded articulated combinations with high centres of gravity were tested on a specially-constructed tilt deck. Parameters including lateral load transfer at each axle group, deflections of the sprung and unsprung parts of the suspensions, movement at the fifth wheel coupling and torsional deflection of the chassis were measured up to the point of first wheel lift. A computer model of the rollover process was also developed. The effects of suspensions, couplings, tyres and chassis on the rollover limit are discussed. Suspensions have the greatest effect, causing the lateral acceleration at rollover to vary from .36 g to .45 g among the range of vehicles tested. Proposals for a standard test of stability are discussed.