A mathematical model of a truck tandem axle suspension and transmission system, with braking and the generation of longitudinal tyre/road forces, is described. The general non-linear equations of the model are linearised, and minimum stability conditions are determined for a range of base vehicle designs and operating circumstances.

The model reproduces the self-excitation which is not infrequently observed in practice, and conclusions are drawn regarding conditions and design features which will promote self-excited oscillations. The mechanism of the vibrations, and their mode shapes are also revealed.

A digital simulation study, including non-linear effects, confirms the findings from the linear model, and provides additional information relating to the development of limit-cycle oscillations and their amplitudes.