Another physics property having to do with airflow around a moving vehicle is called the Venturi Effect. The Venturi Effect states that when a gas or fluid is forced through a narrow channel or area, the gas or liquid will accelerate, and thus create a lower pressure in the channel. Car enthusiasts take this theory one step further by installing a channel under the rear of the car known as an underbody rear diffuser.

How Does an Underbody Rear Diffuser Work?     

Here’s how it works. As air rushes under the car, the diffuser will channel the air into a narrow slot. Once inside the narrower area, the air will accelerate, helping it to move even more quickly to the back and out behind the car, creating lower pressure. This generates downforce under the rear of the vehicle while smoothing the airflow under the car, reducing turbulence.

One thing to consider is teaming a rear wing with a diffuser. The rear wing will interact with the diffuser, helping to further lower pressure and promote even more suction to the road.
They’re available in carbon fiber or plastic. Carbon fiber underbody rear diffusers run around $1200.00 from Carbon Creations, while plastic models cost around $700.00.