Inflation Pressure Effects in the Nondimensional Tire Model

Inflation pressure affects every aspect of tire performance. Most tire models, including the Radt/Milliken Nondimensional Tire Model, are restricted to modeling a single inflation pressure at a time. This is a reasonable limitation, in that the Nondimensional model forms an input/output relationship between tire operating conditions and force & moment outputs. Traditional operating conditions are normal load, slip angle, inclination angle, slip ratio and road surface friction coefficient.

Tire pressure is more like a tire parameter than a tire operating condition. Since the Nondimensional Tire Model is semi-empirical it does not specifically deal with tire parameters like sidewall height or tread compound. Still, tire pressure is the easiest tire parameter to change, and as the air temperature within the tire varies during use so does the inflation pressure. Thus, it is desirable to incorporate inflation pressure into the Nondimensional Tire Model as an input.

This paper discusses the effects of tire pressure on tire force and moment output. Effects on lateral force and aligning torque are investigated in detail. Additionally, the effects on cornering stiffness, friction coefficients, peak aligning torque coefficient and peak shape are reviewed. New techniques to implement pressure effects in the Nondimensional Model are presented. Applications of these techniques are shown on a Formula SAE tire and a full-size radial racing tire.

Additionally, the effects of inflation pressure on tire spring rate and loaded radius are investigated. While these are not modeled using Nondimensional techniques, they are important variables accompanying any tire model.