How To Get Better Underbody Aerodynamics For Your Car

Holes in Rear Bumper to reduce Drag.

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When it comes to aerodynamics for drag cars, as the name goes, it’s all about reducing “drag”. So what usual dragsters do nowadays is trim, or put holes on the rear bumber to reduce drag, as the rear bumper tends to act like a parachute for underbody air.

However, drag cars are designed for straight-line speed. Not much downforce is required for cornering. The only downforce needed is to reduce the chance of the tires spinning, while maintaining stability at high speeds.

On the other hand, for circuit race cars, it’s a bit more complicated. You need the downforce even as you go through corners in order to mantain absolute control over the car, and keep the tires planted on the ground. And we’re all familiar with the different types of aerodynamic appendages found on the exterior of race cars, and we sort of know how to visualize how to exploit the air travelling on top of the car. But what about the air that travels underneath?

This is what’s called the ground effect. The theory, as Wikipedia states it, is as such:
“In racing cars, a designer’s aim is for increased downforce, allowing greater cornering speeds. (Starting in the mid 1960s ‘wings’, or inverted aerofoils, were routinely used in the design of racing cars to increase downforce, but this is not ground effect.) This kind of ground effect is easily illustrated by taking a tarpaulin out on a windy day and holding it close to the ground, it can be observed that when close enough to the ground the tarp will suddenly be sucked towards the ground.”

If you want to read all the technical stuff as to how it works, you can read more about ground effects in cars on Wikipedia. But if you want to go directly to the juicy stuff and how to have this so-called ground effect, or Venturi Effect done for your very own car, then read on.

Basically, what you have to achieve is for the air that gets sucked in from underneath the front air dam to flow as smooth as possible through the car’s underside, and then be “diffused” by the rear diffuser.

Essentially, what this means is when the air gets sucked into the narrow space between the front of the car and the ground, the air accelerates. Then as it leaves through the rear diffuser, it slows down. The accelerated air underneath creates a low pressure area that sucks the car down, generating downforce.

Ever wonder why F1 cars have their noses raised above the front wing? It’s to bring more air to the underside of the car to take advantage of underbody aerodynamics.

But then, neither of us own F1 cars. So how do we get to use underbody aerodynamics for our very own beloved rides?

Here’s an example of a correctly done full underbody kit. This unit is a Dry Carbon Kevlar complete bottom diffuser package from Password:JDM Industries.

Flat Underbody.

Air exits smoothly through the Rear Diffuser.

Now, do you want one for your ride?

By the way, who can make a guess what car is shown above? Post it in the comments below.

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