Dynamic analysis of the WESMO FSAE car’s suspension

Over the years motorsport has become a large part of society with many millions of dollars spent on the design and development of the cars. However, with many racing series evening out the playing field between low and high budget teams by introducing restrictions, especially around engine size, suspension and vehicle dynamics analysis have become a big factor in reducing lap times. This is true for high end racing such as Formula 1 down to entry level racing such as Formulae SAE, a racing series where tertiary students design and manufacture single seater race cars. The following research was centred on the vehicle dynamic analysis of the SAE car manufactured by the University of Waikato in Hamilton, New Zealand, in 2018. In particular, the focus was on suspension tuning and understanding the relationship between suspension and tyre parameters. Theoretical models were developed based on geometric data and tyre data available for the car. Furthermore, the effect of spring rate, camber angle, tyre pressure and damping rates on traction coefficients were investigated. A low tyre pressure (8 PSI), as well as a high pressure (14 PSI), reduced the lateral force capable of being produced during cornering. A softer spring at the rear (225 lbs/in) allowed more grip and a stiffer front (250 lbs/in) allowed for a good response during steering input, whereas a change in camber between 0° and 3° was negligible on the traction coefficient. The theoretical models were verified using track data gathered by sensors on the car and logged through a CDL3 MoTeC dash data logger. The lap time for a 1.2 km track could be decreased by up to seven seconds by tuning the suspension parameters to increase the grip of the car during cornering. This was achieved by decreasing the low speed rebound damping on the shocks to allow more compliance between the road and the tyre reducing understeer. Different methods of diagnosing understeer were investigated as the car did not have a yaw sensor. A comparison between front and rear tyre slip angles (calculated based on logged data) gave the most accurate results compared to purely investigating the steering wheel angle or calculating the difference between wheel angle and Ackermann angle. Furthermore, the amount of roll was optimised by implementing a soft antiroll bar at the front and the rear of the car, allowing enough roll for driver feedback but limiting it to eliminate jacking of the wheel. Overall the beneficial effect of correct and in-depth suspension tuning was found to be substantial. Good tuning, however, is not a remedy for badly designed suspension. The 2018 WESMO car had a well-designed suspension, making tuning possible and beneficial. If the 2018 car’s suspension had been tuned properly, the team could have potentially placed third instead of eighth in the autocross event at the 2018 Formula SAE competition at Winton Motor Raceway in Australia