The Effects of Local Spring Perch Flexibility on Suspension Geometry of a Winston Cup Race Car

In order to achieve predictable handling of a race car, local mounts connecting suspension components to the chassis should be sufficiently rigid to minimize unwanted local deflection which may adversely affect suspension geometry. In this work, the effects of local chassis flexibility of the spring perch on roll stiffness, tire camber change, and steer angle change are determined from a finite element model (FEM) of a Winston Cup race car. Details such as side gussets, supporting brackets, and local curvature of the frame rail spring pocket are included in a shell model of the spring perch. The local shell model of the spring perch is integrated with the global finite element stiffness model of the chassis and suspension consisting of an assembly of beam and shell elements. A parametric study on the effects of thickness changes for seven different areas of the spring perch has been performed. Tire camber change, steer angle change, and chassis roll stiffness are plotted as a function of thickness variation for each of the seven perch areas. Results indicate that the surface with the most adverse affects on torsional stiffness, roll stiffness, and camber changes, resulting from reduced thickness, is the principal spring support plate. Stiffness increases may be achieved by increasing the thickness of the spring plate, spring pocket, and frame rail box beam, but the greatest benefits result from otherwise fortifying the spring pocket and box beam. The frame rail box beam and spring pocket exert tremendous influence on steer angle behavior, and can increase roll stiffness and minimize camber change if properly reinforced.