APR Vortex Generators help to guide the air flow on cars with very steep drop-off angles between the roof and the rear window. Air flow has a tendency to become turbulent as it separates from the surface of the car in this region. This turbulent air causes drag and reduces the effectiveness of a rear wing. The APR Vortex Generator helps to reduce drag and improve the effectiveness of the rear wing by delaying the air flow separation and reducing turbulence. to your 2015-up Subaru WRX/STI