January 26, 2023 2 min read

Improving aerodynamic efficiency is one of the biggest priorities for serious racing teams. Whether its homemade front splitters or advanced CFD tested designs, using airflow effectively can improve grip and lower lap times. Poor aero can limit top speed, reduce grip, and make a car difficult to drive.

So how do you know if your aero is working for or against you?

First, the basics. The main goal is to add downforce and reduce drag. Secondary goals are to ensure that the car is balanced, consistent, and predictable.

The higher the load on a tire, the more cornering force it can generate (though the relationship of load to cornering force is nonlinear). Increasing tire load without increasing vehicle mass is why downforce is important.

Downforce and lift are generated via air pressure differentials. Faster air on the underside of a wing creates a low pressure area, resulting in downforce.

Drag is the result of pushing the car through air. Making it easier for air to flow around a car and filling in the wake behind a car will reduce drag.

Both downforce and drag are proportional to the square of vehicle speed, so their effects increase quickly at higher speeds.

Subaru rendered car with CFD simulated airflow

Most cars have a body shape similar to an airplane wing and generate lift in their factory form. We can add aero devices to counter their natural shape.

A properly designed rear wing can produce massive downforce, with a drag penalty. Features like end plates, swan necks, and gurney flaps can improve the lift/drag ratio of a wing.

The main aero device up front is a splitter, which creates a low pressure area under the car. A larger and lower splitter is usually a good thing, but that tends to be a problem for a street car.

Splitter end plates are used to direct air around the side of the car, potentially reducing drag and lift. Canards and dive planes can complement the front splitter to add downforce or direct air around a car, at the expense of drag.

At the top levels of motorsport, half of a car’s downforce can come from the underside. Properly designed flat bottoms and diffusers allow air to move quickly under the car with minimal turbulence. The diffuser helps to speed up air at the rear of a car, creating a low pressure area and rear downforce.

Simply changing a car’s ride height (and adjusting front to rear chassis rake) can alter underbody aero performance.

A properly designed rear diffuser can improve the overall downforce/drag ratio.