ABSTRACT

Tire force generation is often described in terms of a steady-state force response, which is considered independent of time and a function of the kinematic roll conditions such as slip angle. In addition to the steady-state response, the tire also exhibits a time-dependent transient force response, which in the lateral direction is a delay in the buildup of the cornering force. This delay is often characterized by the so-called tire relaxation length (RL) (Ly), a tire performance characteristic often thought to have a strong effect on handling performance. The definition and mechanistic interpretation of tire lateral RL is discussed, and different methods for measuring and interpreting lateral RL are compared. The measurement methods include different types of flat belt as well as static stiffness measurements. Because of different levels of measurement uncertainty, the repeatability and benefits of the different measurement methods are demonstrated. To determine the effect of including tire transient response in tire/vehicle system models, a handling study was performed. The study included a series of CarSim handling simulations with tires of different transient force and moment characteristics as well as an analysis of outdoor subjective handling ratings. The results show the relatively small contribution of tire transient characteristics to vehicle handling performance compared with the tire steady-state force response.

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