All About Automotive Aerodynamics

Aerodynamics is the study of how air moves around objects. Much like a speeding car creates a trail of turbulence in its wake, an airfoil (like an airplane wing) generates lift when it slices through the air. When working with cars, aerodynamics takes on another dimension because the shape of your average vehicle is so irregular. An efficient car design should be smooth and slippery to cut down on wind resistance, aka drag. One way to do that is by adding spoilers or other extensions that divert air away from the body or serve as air brakes while driving at high speeds. These are typically found on race cars, but automakers are starting to add them to regular production models for increased fuel efficiency.

Automotive aerodynamics is only half the battle. Engine cooling, fuel efficiency and tire traction all play major roles in design. With that said, let's take a deeper look into the science of aerodynamics to see how it helps (or hurts) your car's fuel economy.

Aerodynamic Drag

Wind resistance--also known as drag--is one of the biggest factors affecting overall vehicle fuel economy. The Aerodynamic Drag Force (ADF) pushes against your car when you hit the gas pedal or brake, robbing power from your engine and slowing you down in the process. The more air there is flowing around a vehicle, the greater its propensity for drag will be. And a of air flowing over a moving vehicle is directly proportional to the square of its speed. As a result, an object moving at 50 mph experiences four times more drag than one traveling at 25 mph.

The major contributors to overall aerodynamic drag are the front and side windows along with the windshield. Other culprits include large mirrors, roof racks or antennas that stick out from your vehicle. Loose-fitting clothes can also make you less aerodynamic while driving which is why professional racing drivers wear tight-fitting driver suits made of polyester or similar materials. Most cars have become slipperier thanks to rounded body shells and more sculpted designs over the years, but there's still some room for improvement if automakers want vehicles that are ultra-efficient.

Drag Coefficient

Aerodynamic drag is quantified by the drag coefficient (Cd), which is the ratio of the amount of aerodynamic drag to the force created when moving at a certain speed. The lower the number, the more streamlined your car becomes. So when you're cruising down the highway, an efficient engine will help reduce overall friction and wind resistance so that less energy is wasted -- resulting in better fuel economy.

Factors Affecting Drag Coefficient

The shape of your vehicle plays a big role in its Cd calculation. If you've ever seen pictures or footage of vehicles traveling through water, you'll notice they can glide through much easier than if they were on land because virtually all land vehicles have flat surfaces to cut through the air. However, cars that come into contact with water (like the Jeep Wrangler) have a much higher Cd because they're built like small rafts and allow for more drag while moving. This is also why some sports cars and sedans look sleek and slippery when standing still, but less aerodynamic when traveling at speed.

Other factors affecting your car's Cd include:

・Coefficient of Friction - The amount of friction between two surfaces in contact with one another

・Profile Drag - The additional drag caused by air passing around protruding parts such as mirrors or antennas on your vehicle

・Interference Drag - Energy that is lost due to various paths taken by air through or around an automobile