The Effects of Chassis Flexibility on Roll Stiffness of a Winston Cup Race Car

Predictable handling of a racecar may be achieved by tailoring chassis stiffness so that roll stiffness between sprung and unsprung masses are due almost entirely to the suspension. In this work, the effects of overall chassis flexibility on roll stiffness and wheel camber response, will be determined using a finite element model (FEM) of a Winston Cup racecar chassis and suspension. The FEM of the chassis/suspension is built from an assembly of beam and shell elements using geometry measured from a typical Winston cup race configuration. Care has been taken to model internal constraints between degrees-of-freedom (DOF) at suspension to chassis connections, e.g. t ball and pin joints and internal releases.

To validate the model, the change in wheel loads due to an applied jacking force that rolls the chassis agrees closely with measured data. The roll stiffness predicted from finite element models of the front and rear suspension compared closely to those calculated using a rigid-body kinematics model. To study the effects of chassis flexibility on roll, torsional stiffness is increased by adding strategic members to the chassis structure. Results from the finite element analysis indicate that the effective roll stiffness of the front suspension interacting with the chassis, increased by 7.3 % over a baseline chassis when the chassis torsional stiffness was increased by 130% over a baseline chassis stiffness of 9934 ft-lb/deg. As the chassis stiffness is increased further above this value, the front roll stiffness changed very little. From these results, the minimum torsional stiffness required so that the effective roll stiffness of the front suspension is within 3 % from the roll stiffness with a rigid chassis, is about 23100 ft-lb/deg.