Transient Tire Properties

This paper identifies and analyzes steady-state and transient tire properties affecting vehicle directional response characteristics. The study is limited to the relationship between lateral force and slip angle. It shows fundamental differences between steady-state and transient properties. Tire transient properties are described by a force-slip angle loop with cornering stiffness and dynamic lateral force offset as parameters. Cornering stiffness is presented as a variable that changes with speed and steer rate. An interrelationship between cornering stiffness and dynamic lateral force offset resulting from the time lag between lateral force and slip angle is shown. Ramp steer techniques for measuring transient tire properties on a road trailer and on an external drum machine are described. A need for transient tire data for computer simulations of vehicle transient steer maneuvers is shown. Subjective evaluations of a vehicle equipped with different tires are described and compared with results of evaluations of 21 foreign and domestic vehicles.

The significance to vehicle handling of tires having different characteristics, as determined by subjective evaluations in a lane change maneuver, is shown. Correlation between measurements of tire properties and subjective evaluations may be feasible with additional work utilizing a larger test sample size, improved test devices, and additional test criteria.