Technology Countdown: Aerodynamics

March 26, 2013, Pat DeCola,

As manufacturers use air flow in their favor, cars gain efficiency

Read more: Mobil 1 Technology Hub

Ah, remember the good ol’ days?

Cue Junior Johnson’s Pontiac barreling down some dirt track in North Carolina, teaching his competitors first-hand the true art of driving an automobile; the rumbling of engines apparent as they breathe for air amidst a cloud of smoke and dust clouds; the big, beautiful, boxy cars cutting through the wind as well as a jogger in a swimming pool.

For those whose memories are slightly foggy -- or, more likely, just weren’t around in 1955, myself included -- the featured vehicles seen in NASCAR weren’t always as aerodynamically-sound as today’s Generation-6 car, which debuted earlier this year. While Johnson is universally credited with patenting early drafting strategies, the sport had a long way to go over the course of the next 50-plus years. As technology developed and cars were fine-tuned, the goal became to produce a car with minimal wind resistance, or, at least a car that uses wind to work in its favor.

At its core, aerodynamics is a basic concept. It can be boiled down to the tendencies and motion of air as it interacts with a moving, solid object. Of course, there’s a lot more to it than that, especially when it comes to how NASCAR vehicles are designed to use aerodynamics to gain an advantage.

There are three principle aspects that teams account for when attempting to build the most aerodynamically-sound vehicle: downforce, skyward force, also known as lift, and drag.

Downforce is created when air pressure weighs on the car from above, creating a stronger bond between the tire and track. This results from differences in pressure from both sides of the car. The benefits come when the downforce is greater than the skyward force, allowing the car to hold on to the track firmly.

As air pressure builds underneath the car, more skyward force is created, increasing the risk of a car losing control. Teams take this into heavy consideration and account for it by lowering the nose of the vehicle as close to the ground as possible to reduce the amount of air that can flow through the undercarriage. By doing so, most of the air the car comes in contact with will flow over the hood, windshield and roof, creating a low pressure, isolated vacuum underneath it. For the air that does end up underneath the vehicle, the goal is to create a way for it to escape easily in order to reduce any possible lift.

Naturally, as air passes over the car much of is lost from nose to tail, causing an imbalance in downward pressure from end to end. In order to combat this and equally distribute the amount of downforce a car is subject to, spoilers were developed to hold air on the back end of the vehicle and ensure that a car does not lift from the rear.

NASCAR automobiles experience drag when the force of incoming air interacts with the body of the car, opposing the car’s force. This creates a strong resistance, so manufacturers create a sleek body that will allow air to naturally flow over and around the car and create minimal drag. The less drag a car is exposed to, the less horsepower it requires to move the car, increasing fuel efficiency and overall speed.

The aforementioned drafting, also known as slipstreaming, occurs when a lead vehicle is being closely followed by another vehicle and air flows over both cars, cutting down on the drag induced by the follow car. This style of racing can significantly reduce the energy used by the follow car and will often result in that car passing the lead car.

Just like Junior Johnson drew it up.