Having a well-balanced suspension in race cars is critical to a team's success in every race series. The ability of the suspension to keep all four tires in contact with the racing surface over bumps and through turns is crucial. A key component controlling these factors is the dampers. One method used to assess the damper performance, besides on track testing, is the four post vibration rig test. This test involves placing the vehicle on a four post test stand that inputs prescribed forces to the four tires. Acceleration measurements are made on the car during this test and frequency response plots can be generated to evaluate the vertical dynamic response of the vehicle.
While very useful, the four post rig testing is expensive both in terms of race team time and costs. This inspired us to develop a computer simulation of this test that would allow the user to quickly run through many damper and suspension configurations and analyze the predicted vertical dynamic response of the vehicle. Both linear and nonlinear computer simulation models were developed, with the nonlinear model using actual force versus velocity characteristics for the dampers as measured from cyclic testing. Simulation results show good correlation between the actual four post vibration testing and simulation results for an IMSA GTP car. The simulations were also used to tune the dampers of an Indy Lights Lola car by altering the existing damper characteristics to get the desired dynamic response of the vehicle. This procedure was used successfully in the 1993 Indy Lights racing series to tune the dampers for the cars of one team.