Talk to any motorsport fan long enough, and you’re likely to hear two things. One, dirty air is a bad thing, and two, slipstreaming is good. In theory, they’re basically the same thing: one driver is following behind another. But the reality is, like all other things, far more complex. And after a handful of slipstreaming races this year, it’s time to look at those concepts in depth.
To accompany our excellent chat today, we have a video by Chain Bear which, as usual, goes into all the physics, math, and science bits that I couldn’t articulate with half as much grace or clarity:
I think one of the smartest things Chain Bear does here is compare air as F1 cars experience it to water; it feels thicker and more resistant as you travel faster. It helps make sense of why F1 cars have the aero designed the way it is; you want to keep it as equal as possible, since sticking any bits out to one side will pull the car in that direction (which is, coincidentally, why many stock cars are designed so asymmetrically).
And, as physics demands, drag increases exponentially with speed. So, the faster you go, the more resistance you’ll feel on the car. That means F1 cars also punch a pretty serious hole into the air around them. Tucking up inside that hole behind a front car means that the front car takes the brunt of the buffeting from the air and has to work harder to achieve speed. The following car, meanwhile, has to work a lot less harder and can even use that clear air to slingshot around the front driver. The front driver is experiencing a higher amount of drag than the following car, which means the follower can take advantage of better acceleration.
As you can tell here, the slipstream is actually kind of a lack of air; it’s a low density pocket where the following driver isn’t experiencing the full force of the air’s drag.
Dirty air, meanwhile, is the exact opposite. Instead of creating a handy hole behind it, the lead car is sending air in all sorts of wild and crazy directions, which then buffet the following car. That changeable air then messes with the aerodynamics of the F1 car, which depend on a consistent and steady stream of air. In that case, the lead car has the advantage because it has the consistent air while the followers are trying to gain consistent grip in some pretty chaotic situations.
The way F1 cars are designed, you’re more likely to have a chaotic stream of air channeled out to the rear of the car than you are to have a basic car that just cuts one basic hole in the air. That’s why you’ll get dirty air where you think there would be an empty pocket; the car is shoving all the turbulent air in weird directions behind it, which makes it difficult for a following car to get too close.
So, yes — you could boil it down to something as simple as “one car follows the other,” but as we all well know, there’s nothing simple about F1.