This paper is an investigation into the usefulness of aerodynamic devices, specifically under trays, on Formula SAE vehicles, where the average running speed at competition is relatively low (54km/h).Using basic fluid dynamic principles and Matlab as a computational tool, a program was written which attempt to predict the flow conditions over an under tray of a give size and profile. Based on the results of this program a theoretical model was designed and built which it was hoped would produce significant amounts of down force.The theoretical model predicted that the under tray should be able to produce in the vicinity of 1000N down force with the skirt sealed to the ground, or somewhere in the vicinity of 300-500N with the expected skirt gap.The experimental wind tunnel testing used a symmetric model set up to simulate the moving ground, and found that the down force produced was in fact no more than 50N at 11m/s (40km/h).There is no rock solid evidence to prove it, but the results strongly suggest that the reason for the drastic variation between theoretical and experimental data is that the full capture area of the under tray is not being realized. In fact only about a third of the contraction area seems to be getting used to any effect.As a result of the wind tunnel test results, the planned manufacture of a carbon fibre under tray for track testing was cancelled, which saved the project hundreds of dollars in materials and many hours in fabrication time.If a way can be found to realize the entire capture area of the contraction, then the potential aerodynamic gain is enormous.