On the equivalent wheelbase of a three-axle vehicle

The steady-state handling properties of a rigid vehicle with a tandem rear axle configuration are developed. This work uses conventions resulting in a parsimonious characterisation of steady-state handling of such three-axle vehicles that is shown to be a simple extension of the well-known two-axle bicycle model. Specifically the concepts of understeer and wheelbase are developed for a three-axle vehicle, and shown to play the same role in characterising vehicle handling as they do in the well-known two-axle vehicle model. An equivalent wheelbase of a three-axle vehicle is expressed in terms of vehicle geometry and cornering stiffness of each axle. The model developed in this work is reconciled with previous models that make use of simplifying assumptions found in the literature.