The equations of motion of the two degree-of-freedom model of a two-axle road vehicle are expressed using vehicle cornering stiffness constants, which shows the effect of speed more clearly than stability derivatives. The forms of the equations of motion, for analysis in earth-fixed axes and vehicle-fixed axes, are compared. The properties of the characteristic equation are analysed by analogy with the single degree of freedom vibration equation. The undamped natural frequency, damping ratio and damped natural frequency are investigated. A simple extension of the model is considered, allowing inclusion of effects such as roll steer.