Another look at the static stability factor (SSF) in predicting vehicle rollover

Abstract

We consider once again how the static stability factor (SSF) may be a predictor of vehicle rollover propensity. The SSF is known as a vehicle's track width (t) divided by twice the height (h) of the mass centre above the ground (t/2h), while the vehicle is empty and at rest. We define ‘rollover’ as a 1/4 axial rotation, or equivalently at the point where the mass centre reaches its highest position above the ground. Although some have questioned the efficacy of the SSF in predicting rollover we present another approach providing additional insight via a dynamic analysis of a ‘barrel-roll’, and via the introduction of a new parameter called the ‘dynamic stability factor’, defined in the same way as the SSF, but for the dynamic case. The analysis shows that the SSF is a prominent term in the governing equations of motion. But then in examining the stability of a critical solution of these equations we show that we can predict rollover in terms of the SSF, the tire/roadway friction, and the initial roll angle.