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The October SAE Arizona Section was very fortunate
to have Mechanical Engineer Mike Halpin provide an
excellent technical presentation on Racecar Suspension
Design. In the audience were many attentive members from
our student sections, who were also provided handouts to
take back and use to guide their vehicle setups. Over fifty
members, students and guests attended the meeting.
Mike started with the basics with a discussion on single degree of freedom system formulation and dynamic response (mass, spring, damper) showing effect of damping adjustments. Next was the formulation for the effective wheel spring rate, which is not obvious. The effect of damping ratio was examined in charts showing how a suspension model reacts to compression and rebound damping adjustments. The discussion went deeper into how shock absorbers (dampers) actually work, their design and detailed effects upon suspension dynamic response. Low speed damping is controlled by bleed valving (needle type), after a certain piston velocity, the shim stack seal is opened and a large volume of fluid can move under piston pressure. Mike showed the force vs. piston velocity curves for a number of different types of dampers where it could be easily seen how all the adjustments on the units changed the response. The curves are from Mike's own shock absorber dynamometer, his own design. Actual road racecourse data from a MOTEC system was shown from a car Mike drives . The action of all four wheels as they traveled through the corner was examined one could see where there was overshoot, undershoot and very importantly, the actual normal forces being applied to the wheels. Mike discussed how the racecar performance over the entire racecourse can be examined. Mike showed us his own vehicle suspension analysis spreadsheet and how it is used. He illustrated two cases: one where the selected shock could not perform to optimize the car performance on the course and a second that did meet the requirements. Mike emphasized a process that is followed to tune a racecar's suspension where lastly the damping is adjusted. There are quite a number of inputs to understand and quantify. Finally, Mike discussed his guidelines for trackday tuning (provided in the handout) where the many variables are shown and how the work together to tune the vehicle based on results on the track. We all enjoyed the fine presentation and many of us is also the owner of Suspension Research and Development (SRD), Inc in Scottsdale, Arizona. |
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Last Revised: November 5, 2005 Comments, suggestions? E-mail us! |
October 21, 2005