Race car aerodynamic design and improvements enhance the performance of a race car. However, the use of aerodynamic devices by FSAE collegiate teams have been largely minimal although design requirements in Formula SAE (Society of Automotive Engineers) do allow the inclusion of aerodynamic or ground effect devices (rear and front wings, under tray and diffusers) to enhance vehicle performance. This is largely due to design complexity and lengthy hours needed to develop a design for these devices. Subsequently, this issue has prevented several FSAE teams from implementing the design of ground effect or race car aerodynamic devices. However, this research work has devised a much simpler and accurate process in conducting Computational Fluid Dynamics (CFD) simulations. The CFD analysis method devised involves the gradual buildup (bottom to top) of the Computer-Aided Design (CAD) vehicle geometry with each geometrical block in the geometrical buildup ladder simulated sequentially to provide a better understanding and analysis that conforms to aerodynamic principles. In this research work, the under tray design of the Cornell Racing ARG10 car was presented with analysis using CFD simulations and its subsequent validation and verification with on-track testing of under tray prototypes on a full-scale car model. The CFD simulations and on-track testing where conducted for diffusers with varying angles (9°, 14° and 20°) at an average speed of 45 mph and 1 inch ride height. Though a 35% difference in down force data was recorded comparatively between both testing regimes (CFD and on-track testing) for the diffuser angles, the data generated from both testing setups indicate a down force improvement as the diffuser angle is increased along 9°, 14° and 20 with a lap time simulation indicating a 1.5% average lap time improvement with the use of an under tray.