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What Is Bump Drafting? Is It Legal?

Oval stock car racing is fast and exciting. However, if all the cars on the circuit are travelling at the same speed it can become difficult to overtake. This is where the controversial technique of bump drafting comes into play.

Bump drafting is the act of slipstreaming the car in front and kissing its rear bumper instead of pulling out of the slipstream. The bump can cause the leading car to lose traction and the driver will need to lift off the throttle, giving the chasing car a speed advantage.

Bump drafting has become an extremely controversial technique. Many drivers have pointed out the dangers involved in using it. The technique has also inspired tactics that are used to take down fleeing cars in a police chase. Below, we take a closer look at bump drafting in different motorsports.

How Does Bump Drafting Work?

Bump drafting works in two main ways. It all comes down to aerodynamics and physics. It can be executed relatively easily, especially on fast oval circuits where you can get really close to the car in front of you.

The first phase of bump drafting is the slipstream. Slipstreaming, or drafting, is when a car pulls in behind another one and uses the decreased air resistance behind the leading car to go faster. This happens when the car in front is able to effectively punch a hole in the air.

The Slipstream Effect

The car in front has to push through ‘thicker’ air. This causes air resistance, or drag. This creates a vacuum for the car behind that can travel through ‘thinner’ air – in reality it’s an area of lower pressure – allowing it to move significantly faster than the car in front, as it experiences less drag. However, you need to be close enough to the car in front in order to catch a slipstream.

As the chasing vehicle will be travelling faster than the leading vehicle, it will naturally close the gap between the two. Once the chasing vehicle gets close to the leading vehicle there is an ‘air bubble’ in between the two cars.

This air bubble can be difficult to break through. The best place to get through the air bubble is coming out of a corner leading onto a straight. If you get a better exit than the car ahead, you can force your car through it.

The Bump Phase

Once your car breaks through the air bubble, you will ‘bump’ the car in front. This kiss on the rear bumper will unsettle the car in front. The action of the bump results in the rear of the car lifting very slightly and quickly off the ground.

What happens in that split second is that the rear wheels will spin slightly. As they are spinning faster than the travelling speed when the re-join the ground, they will lose traction and slide on the surface of the tarmac.

When the rear tires lose traction, the rear of the car will become unsettled, and the driver will need to slightly lift their foot off the throttle in order to regain traction and control over the rear axle of the car. When they lift their foot off the throttle, their car will lose some speed. This gives the chasing car the perfect opportunity to make an overtaking move into the next corner.

Is Bump Drafting Effective?

Bump drafting is an extremely effective tactic if you are trying to overtake the car in front. The action of bump drafting makes the chasing car faster while slowing down the leading car, which is ideal for overtaking.

Bump drafting is so effective in fact, that it led to the police force adopting the technique and turning it into the PIT manoeuvre (Pursuit Intervention Technique). Although, in their case they would be looking to stop the leading vehicle rather than overtake it.

Even drafting on its own is an effective way to overtake other cars. The speed advantage from drafting alone is enough to achieve a higher top speed than the car in front of you. In most cases, you will only see normal drafting being used, rather than bump drafting.

Is Bump Drafting Legal?

Bump drafting was banned from NASCAR in 2014 after the technique caused a car to lose control and crash into the catch fencing. Ultimately, the safety of the drivers and spectators is of utmost importance.

Bump drafting is an extremely dangerous technique. Over the years it has been a controversial topic. Many drivers have stated that it is too dangerous to allow it to be used in motorsport. Others have argued that it makes the racing better and much more exciting.

Overall, bump drafting is very effective, but too dangerous to allow in motorsport. When a car loses control it can have extreme consequences, especially when it is leading a pack of more than 20 other cars.

Do You See Bump Drafting In Other Forms Of Racing?

Bump drafting has been a technique that is mostly used in oval racing and stock car racing. It became popular in NASCAR, and it hasn’t been used in many other forms of motorsport over the years. There are some very good reasons for that though.

In most other forms of motorsport, oval circuits aren’t used. This makes it difficult to get as close to the car in front and match their speed for an extended period of time. Many circuits do not have a straight long enough for bump drafting to be effective.

Other forms of drafting are used. However, you do not see the bumping effect happening very often. In some cases, you might see it with sports cars when they race on circuits that have long straights, such as Le Mans.

Single Seater Racing

You will never see any form of bump drafting in single seater categories like IndyCar or Formula 1. That’s because the cars are much more fragile. If you bump into another car on the straight, it’s a sure-fire way to lose your front wing and destroy the gearbox of the car in front of you.

In addition, the slipstreaming effect in single seater cars is extremely powerful. Due to the aerodynamics of the cars, it can be more than twice as powerful than slipstreaming in cars that have a standard shape.

Therefore, there is no need to use bump drafting in single seater cars. The chasing car will have a massive speed advantage to the car in front just by being in its slipstream. In some cases, they can be up to 20 miles per hour faster just from gaining an effective slipstream.

What Are Alternatives To Bump Drafting?

Since bump drafting is now illegal in NASCAR, frowned upon in sports cars, and effectively unusable in single seaters, drivers have to make use of other forms of drafting to overtake cars. Over the years, other tactics have also been developed.

In NASCAR, side drafting is now also an effective tactic. It is more difficult to pull off, but it can have a similar effect to bump drafting. It is a much safer alternative to bump drafting since it does not cause the leading car to lose rear stability.

Side Drafting

Side drafting involves pulling the nose of your car right up to the inside rear wheel of the car in front. Although you won’t benefit from the vacuum of the leading car, your car will be creating its own wake of air.

The wake from your car will push air into the rear wing of the leading car. This causes more drag on the leading car, which will in turn slow it down. Pulling away from the leading car heading into corner will send turbulent air onto the rear wing of the car next to you and slow down its cornering speed.

Slingshot

Another form of drafting overtakes is called the slingshot. This is the more common form of drafting that we see in modern motorsport. Pulling in behind the leading car will allow you to pick up the slipstream and help you to gain speed.

Once you get right behind the leading car, you need to pull out into the clean air swiftly and smoothly. The closer you can get to the braking zone the better. Pulling out of the slipstream before you get to the air bubble will allow you to keep increasing the speed of your car further instead of just matching the car in front.

DRS

In single seater racing such as Formula 1, technology has been developed to improve the overtaking opportunities on straights. The drag reduction system, or DRS for short, is a panel on the rear wing of the car that opens on the straights.

When the panel on the rear wing opens, more air will flow through the rear wing rather than going straight into it, and the overall drag of the car is reduced. As soon as the driver pushes down on the brake pedal, the rear wing panel closes to add downforce and help the car slow down again.

There are rules to using DRS. There are designated DRS zones on the racetrack, and you need to be within 1 second of the car ahead for your DRS to activate. This makes it more difficult to use and prevents it from being overpowered.

Final Thoughts

Bump drafting involves slipstreaming the car in front and nudging it forward, pulling you along with it, and usually causing the lead car to slow down slightly, making it easier to pass. However, the result of some serious accidents led to the technique being banned from most forms of motorsport.