What Does a Diffuser Do on a Car?

December 5, 2023

A diffuser is a shaped part of a car found on either the rear underside or closer to the front underside near the wheels. It is often sloped downward from front-to-back and may include vertical fins which help to increase downforce. It is the most important aerodynamic device to maximize the ground effect which improves traction and stability while decreasing drag. It is also the component which helps to regulate the sensitivity of the car to track conditions and weather, an integral aspect of Formula 1 racing.

The principle of how a diffuser works is based on Bernoulli’s Principle, which states that as velocity increases, pressure decreases. This is the primary function of a diffuser. The car underbody is a turbulent flow of air with lower pressure than the ambient air, and the rear diffuser aims to normalize this pressure difference in a similar manner to an airplane wing or a car’s rear spoiler.

The sloped surface of the diffuser accelerates the flow of air, which decreases the overall pressure. This reduces turbulence under the car, and allows it to move faster. However, this can create a problem, and the angle at which the diffuser is positioned plays an extremely important role in its effectiveness. If the angle is too shallow, the flow may separate from the underbody, and the downforce will decrease. If the angle is too steep, a large amount of induced drag will be created, which can also negatively impact the car’s performance.

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