What’s Happening?

You hear it all the time on a broadcast, and you hear drivers loathe it all the time, dirty air. But, what exactly does that mean? What exactly makes the air “Dirty”? Well, today, we explain what “Dirty Air” actually is.

• Dirty air has absolutely nothing to do with the actual cleanliness of the air. It has to do with the aerodynamic properties of a race car.
• Therefore, in order to understand “Dirty Air”, it’s important to understand aerodynamics. That’s ultimately what everything is built upon.
• Fans like to throw around the term “Dirty air” because it does negatively impact the racing product. However, fans may now know exactly what it means.

How Aerodynamics Work

Aerodynamics is a very complicated thing, but, it’s essential to understand how it works in order to understand dirty air. Essentially, aerodynamics is about how air flows over the race car, and it’s essential to making a car go faster. While horsepower provides the power needed for a car to go fast, aerodynamics allows the car to cut through the air, which helps increase the speed of the car.

For example, if you look at the new Ford Mustang Dark Horse, you’ll notice fender flares just above the wheel wells. The smooth, sleek shape of the car also allows the car to cut through the air better than a boxier car will. If a car does not have good aerodynamics, it creates what we call drag, which causes the car to slow down.

The caveat to all of this is that the aerodynamic design of the cars is meant to function with clean, unobstructed air flowing over it. Look at a wind tunnel, for example, and you see that the car’s aerodynamics work well when the undisturbed or “Clean” air flows over the car. Steve Letarte also gives some deeper insight into how a wind tunnel works.

However, the aerodynamic properties of a car also play into how “Dirty air” works. Now we get into what “Dirty air” means.

What Is Dirty Air?

“Dirty Air” is created by the air coming off of the back of a car. Instead of clean, unobstructed air, the air bounces all around in vortexes, which creates a turbulent airflow behind the car. If you’ve ever experienced turbulence in an airplane, that’s exactly what the cars have to confront when coming up behind another car. You’ll often see bodywork on the car buffeting in the turbulent air behind another car, and, it has created some treacherous scenarios.

Since the air is very turbulent or “Dirty”, the aerodynamic parts of the car that are designed to hold the car down through the corners cannot work. With the resulting loss of downforce, the behind ends up “Pushing” up the track in what they call an “Aero push”.

This is why drivers move around to other grooves on the track when they get close to another car. They are trying to get out of the turbulent wake of the car in front to get into the clean air. Coincidentally, the car in front tries to get in front of the car behind to disturb the airflow. One great example of this is the battle in the closing laps between Kyle Larson and Tyler Reddick at Las Vegas this season.

Now, the flip side of this is that, on the straightaway, the cars don’t have as much air to work through to go in a straight line. This is where “Drafting” comes into play, and it allows the trailing driver to pull up down the straightaways thanks to the hole punched in the air by the leading car. The problem is that, once you get to the corner, there’s not as much air to create downforce, which creates the aero push.

Dirty air is a very complicated thing, but simply put, it’s the turbulent airflow behind a car. The turbulent air does not allow the aerodynamics of the trailing car to work properly through the turns, which causes that car to lose grip.

Dirty air is very common on high-speed tracks, so, fans will hear that phrase a lot. No one really likes to talk about dirty air, but, it does exist whether we like it or not.