1 Genetic Algorithm for Tyre Model Identification in Automotive Dynamics Studies DAVID VETTURI, MARCO GADOLA, LUCA MANZO, RODOLFO FAGLIA Mechanical Engineering Department Univeristà degli Studi di Brescia Phone: ++39 30 3715426 - Fax ++39 30 3702448 E-mail vetturi@bsing.ing.unibs.it 96VR024 Abstract The identification of the values of the Pacejka tyre model parameters, starting up from a set of experimental available data, results quite difficult. The present work shows a genetic algorithm based methodology for the determination of these coefficients. After a description of the general genetic algorithm procedures, the application to the case of the model of the tyre are presented. The main advantage of the described method, not shown by other algorithms, lies in the possibility of determining numerically the Pacejka coefficients also starting from a bad estimation of the parameters. 1. Tyre Representation As Sharp states [4], tyre forces and torques, provided by the friction between tyres and ground, are of primary importance in vehicle handling. Tyres usually provide the dominant external forces on the vehicle and therefore largely determine its motions. For this reason vehicle models depend on appropriate representations of tyre behaviour being available. A basic tyre model for handling simulations should take into account three fundamental components: lateral force and self-aligning moment, depending on sideslip, and longitudinal force depending on longitudinal slip. Lateral force is the key to roadholding, hence is necessary for either steady-state and transient response simulations. Self-aligning moment is quite useful to determine steering effort and driving feeling and their relationship with the vehicle behaviour. An effective representation of both longitudinal force components, under brake and driving conditions, is fundamental for a truly complete dynamic model. It should be stressed that what looks like a simple fitting problem, actually requires a strongly non-linear solution in a 3D space or even more. As a matter of fact the components are all depending on vertical load and camber angle as well, which are usually provided as an input to the model. Because of the complex structure of a pneumatic tyre in itself, rolling road tests are the most effective way to determine tyre properties. So various methods are available to describe the tyre force system. Usually, test data are composed of arrays of numbers giving force and