Diffuser

Diffuser is an aerodynamic surface located at the rear underside of a car, behind the rear axle. The diffuser angles upward toward the rear of the car, accelerating the air flowing under the car as it exits. The accelerated air creates a low-pressure zone under the car, which generates downforce by sucking the body downward toward the road.

Diffuser design integrates with the rest of the underbody aerodynamics. The flat underbody (or undertray) channels air smoothly under the car at high speed. The diffuser at the rear accelerates that air upward, completing the venturi effect that creates downforce. Modern race cars (Formula 1, Le Mans prototypes) use highly developed diffuser designs to generate enormous downforce. Production cars use simpler diffusers for moderate downforce gains.

Modern road cars with notable diffusers include the Ferrari SF90, Porsche 911 GT3 RS, Lamborghini Huracan STO, and Aston Martin Vulcan. Aftermarket diffuser kits (often integrated with rear bumper replacements) are popular on track-focused builds. The combination of front splitter, rear wing, and rear diffuser creates a complete aerodynamic package.