In this study, the spoiler effect in a different angle of attacks that makes the maximum downforce is conveyed. Two different
facilities are utilized to set up the experiment. A wind tunnel is used to measure the downforce and drag force, and a water tunnel
is used to observe the velocity profile and flow field visualization. The result revealed that a 12° angle of attack is the optimal angle
for designing the spoiler. Twelve degrees angle of attack provided the highest downforce. This downforce can improve the stability
of high-speed sports car without increasing much drag. Compared to the angle of attack of 5°, the downforce of the angle of attack
equal to 12° increases 233%, but the drag force only increases by 15% in wind tunnel experiments.
Keywords: Angle of attack; Downforce; Drag force; High-speed car; Spoiler