A study on the influences of tyre lags and suspension damping on the instantaneous response of a vehicle

The paper aims to quantify the influences of non-steady state tyre behaviour and suspension damping on the instantaneous response of a vehicle to handling manoeuvres. The influences of such parameters cannot be determined using steady state tests. In the present work, a recently developed methodology is employed, which has been applied in the past to simple transient handling studies. Here, the approach is applied to more demanding situations and the effects of tyre lags and suspension damping are directly related to the under-steer, over-steer, or neutral-steer character of the vehicle under test. To distinguish between the effects of tyre force lags, tyre non-linearities, and combined tyre–vehicle non-linearities, an increasingly complex approach is adopted, which involves the implementation of a linear bicycle model, a non-linear bicycle model, and a ten-degrees-of-freedom (10DOF) non-linear vehicle model. In all cases, tyre-force lags are simulated using the relaxation length concept. The 10DOF vehicle model is validated against experimental measurements and forms the basis for fully non-linear studies. It is shown that even inherently under-steering vehicles may initially over-steer as a result of the delayed response of tyres. Finally, it is demonstrated that the proposed approach captures the effect of suspension damping and some problems are discussed regarding its application.