Notes on a simplified two-degree-of-freedom car suspension model of chassis heave and pitch-plane dynamics

This article considers the derivation of a common two-degree-of-freedom automotive suspension heave and pitch design model involving the front and rear axle coupled and uncoupled spring stiffnesses. Many rules of thumb are used in automotive design regarding this model perhaps without full appreciation of the mathematical analysis and assumptions invoked in their formulation. With the widespread use of computer-aided suspension simulation models, it is perhaps timely to note the derivations of the model equations and the limiting assumptions for which they can be applied with confidence. In particular, the derivations and numerical examples show that the concept of a stationary pitch centre for chassis-coupled dynamic normal-mode vibration analysis is questionable.