There exists a fairly extensive set of tire force measurements performed on dry pavement. But in order to develop a low-coefficient of friction tire model, a set of tire force measurements made on wet pavement is required. Using formulations and parameters obtained on dry roads, and then reducing friction level to that of a wet road is not sufficient to model tire forces in a high fidelity simulation. This paper describes the process of more accurately modeling low coefficient tire forces on the National Advanced Driving Simulator (NADS). It is believed that the tire model improvements will be useful in many types of NADS simulations, including ESC and other advanced vehicle technology studies.
In order to produce results that would come from a road surface that would be sufficiently slippery, a set of tires were shaved to 4/32 inches and sent to a tire-testing lab for measurement. Shaving a tire does not produce the same effects that would come about by allowing a tire to wear down to 4/32 inches through normal use. However, for this study, only the coefficient of friction needed to be reduced. The aging effects of rubber are ignored. Tire forces were measured on a tire test machine, using a water-coated surface to approximate the frictional properties of wet pavement. These tests, which included cornering, braking, and driving, were performed at five loading conditions. They showed a decrease in tire effective lateral stiffness as well as a drop in longitudinal force as the tire speed increased.
The data set from these tests was used to create a tire model for a dynamic simulation. The paper concludes by displaying the model's longitudinal and lateral forces versus loading condition and tire slip angle.