Interpretation of roll plane stability models

Non-linear yaw and roll stability limits are derived for three quasi-static roll plane vehicle models: rigid vehicle, suspended vehicle, and compliant tyre vehicle. A generalised stability equation is developed that fits each of the models when superelevation is included and the use of linearising assumptions is minimised. This generalised stability equation leads to the definition of two new parameters referred to as generalised superelevation and generalised centre of gravity height, which are shown to be physically meaningful. The rigid and suspended vehicle roll stability limits are compared in some detail for a tractor-semitrailer combination. The predicted roll stability limits vary widely, depending on the combination of vehicle parameters.