Understanding Aerodynamic Draft in Racing

Draft or slipstream happens when a race car sits right behind another car and gets less aerodynamic drag, increasing the top speed that that car can reach. The amount of draft effect that you can get depends on the downforce and drag levels each car has and the speed the cars are traveling. That means a Formula One car at 300 power will get a lot more draft than a Mazda MX-5 on a low speed straight.

In some series, this can be the reason you win or lose a race, while in other series the draft does not matter that much. So it's very important that you're fully aware of its existence.

Using Draft on Straightaways

On a straight line, you should always use the draft, even when you don't want to make a pass yet. There are two reasons for that:

Tire and Fuel Conservation

It will help you save tires and fuel. You being 3/10 quicker on the straights means you can save 3/10 in corners worth of tires and fuel. If you do this right, it can be much better grip later in the race.

Just remember that if you're behind someone on a long straight, you will carry more speed, which means your braking reference will be different. So if you don't plan on attacking yet, make sure you brake slightly earlier.

Lift and Coast Technique

An extremely recommended second thing you can actually lift and coast when I race. We say fuel using the clutch and then brake a little bit later to compensate the lower approach speed. With this, we can save more than a full lap of fuel. So we decrease the time needed in the pits and gain an advantage at the end of the race.

The slipstream in this class is insane. Within around a second and a half behind another car, you can gain as much as 15km/h at the end of the straights. And this helps holding the pack together. This means you can stay with the car ahead even if you are around a second lap slower in the corners.

Understanding Lift and Coast

Lift and coast means to lift the throttle earlier than your braking reference and then braking slightly later so you can save some fuel. This is a very important technique.

When you're exiting out of a corner, your speed goes up quickly. But the faster you go, the slower the acceleration because you start getting more and more aerodynamic drag. You reach top speed when the acceleration you get equals the amount of drag the car encounters. So you're trying to push against the air, but the air is pushing you back exactly the same amount, so your speed does not change at all.

At top speed, your fuel consumption is still the same, which makes sense because you're in full throttle. And because of that, when you reach top speed, your fuel consumption efficiency is the worst possible. At that point, lifting for an extra 50m before the corner will make you lose a small amount of time, while bringing your fuel consumption during those 50m to absolutely zero.

It makes total sense to lift and coast if you want to save fuel without losing too much time. But you can only do that at the very end of a long straight right before braking. You should never lift and coast exiting a corner or too far away from a braking zone because your lap time loss will be much higher than the amount of fuel you're saving.

Applications of Lift and Coast

In the end, lifting and coasting works for three things:

• Saving tires if you're behind someone

• Saving fuel if you're behind someone and they are fast and you don't want to fight for a position, so you just want to save fuel so that you can gain time on the pits after in case it's a long race

• Giving yourself an extra breathing room before a braking zone so you can have less chances of hitting someone ahead if you're driving very close to them

In the end, single draft behind another car on straights is always good. The only situation you want to avoid it too much is if you need to cool down your overheating engine and want to avoid the hot air coming from the car ahead.

Bump Drafting Technique

Bump drafting means pushing the car ahead of you on the straight. This works even if your car has exactly the same power as the car ahead. The car ahead is colliding against the air, but your car right behind that car is not, so you get a little bit more speed.

Of course, be careful when you're bump drafting because for some cars it just won't work. The car might be a little bit too fragile and it can be dangerous—it can break your car by trying to do that. But for other cars it's safe to do so and you will have to do it if you want to be competitive in a very close, pack racing situation.

How to Execute Bump Drafting

If you want to bump draft someone ahead, make sure you do it on a long straight and wait before the braking zone. Generally you want to exit the corner very close to the car ahead, start bump drafting throughout the straight, and then you lift and coast right before the actual braking zone. This is the safest way to do it and you can repeat it for as many laps as you want to either catch up with the pack ahead or increase the gap between the guys behind you.

Because remember one thing: fighting for position makes you lose time. Bump drafting is a collaboration technique that makes you both gain time. There's a right time for each—there's a right time to fight, there's a right time to collaborate.

Advanced Draft Strategy

Controlling Draft as the Leading Car

Here's a very important race craft tip: As the leading car you can choose where you place your car to control who you can give draft to when there are two cars battling behind you. Ideally you want people behind you to continue fighting. So if you can give the draft to the car that has the worst track position, that might give them the extra speed that they need to continue fighting, which will cost them even more speed and time and will give you even more breathing room.

Weaving to Break the Draft

What about weaving to break the draft? Can you move around to prevent the car behind you from getting the draft? That's generally not permitted, so if you want to do it you can try to do it very slightly and distract or confuse the driver behind. At higher levels of racing though, this should not have any big effect.

Side Drafting

What about side draft? Let's say you're not directly behind another car but rather slightly behind but with some overlap. You can still benefit from some extra speed by side drafting. The hole in the air that the car ahead punches is not only directly behind it. It also spins slightly to the sides of the car.

The side draft effect is stronger at the back side of the car. So what you can do when you're overtaking someone is stay behind until the very last second, and then you move to the side but staying close to them. So that you can still get that extra tiny boost of speed that can be the difference between you making the pass stick or not. It's a very common mistake to see drivers going all the way to the outside after and not getting that extra tiny speed that they can benefit to finish the move.

Dirty Air and Downforce Loss

Now the same draft giving you an advantage on the straights gives you a disadvantage in the corners. The disturbed air, or dirty air, makes your car have less drag but also less downforce. With less downforce, with less air pushing the tires against the track, there's less traction and your car will have less grip than the car directly ahead of you.

By shifting your lateral position just slightly to the outside of the hole punched in the air by the car ahead, this loss of downforce and performance in dirty air can be reduced. You can kind of visualize a driving line that is shifted half a car to one car width laterally from the lead car.

But of course that will never be fully effective, especially because changing your line might create more problems than minimizing your dirty air. So in the end, you might end up always having problems being right behind some car doing fast corners. Which is why racing has been so difficult and boring in Formula One in the past decade, because they had a lot of problems with dirty air reducing your downforce by like 50%.