Drive

Sexy sleek cars can save you gas money in the long run

Designing a sleek vehicle isn’t just about good looks. A smooth design cuts down on wind resistance, which in turn helps improve fuel economy.

Aerodynamic designs may be obvious on sports cars, but they’re also used on pickup trucks, where engineers face the complicated task of adding wind-cheating tricks without sacrificing work-oriented practicality.

“Air flows over a vehicle, around the side and under it, and you’re trying to make it flow smoothly,” says Jeff Luke, executive chief engineer for global trucks at General Motors. “If the air is turbulent, it results in more drag and it’s less efficient aerodynamically.”

A truck may have an upright grille and stance, but “that doesn’t mean it’s a brick,” Luke says. The bumper and its lower air deflector, and the hood and windshield designs channel air around the truck. Headlights and fog lights are sealed so they deflect the air, instead of trapping it.

Air has to enter the grille to cool the engine, but the engine compartment is designed so the air flows out again, instead of pushing against the firewall.

Under the truck, engineers add body pans, which keep the air flowing so it doesn’t create turbulence against the undercarriage components. If it swirls, it creates aerodynamic drag. This prevents the truck from easily moving forward and requires more fuel to overcome.

Air also has to move smoothly along the sides, where the door handles and window seals play a role. Windshield wipers and mirrors also have to be designed to reduce air swirling around them, which can create annoying wind noise at higher speeds. Even the wheels are designed with flush faces, instead of deep designs that can trap air.

At the rear, a lip on the tailgate helps direct airflow properly. Some people believe that driving with the tailgate down helps improve fuel economy but that’s false, Luke says. Instead, the upright tailgate creates a pressure difference behind the cab. Air flows over this “air cushion,” instead of swirling in the box and creating drag.

“It’s all ‘free’ fuel economy,” Luke says. “The more you focus on every count of aerodynamic drag, the lower you can make it, and so the more fuel you can save.”

Things to note

  • Light. Body pans help reduce wind resistance under the vehicle but must be made of lightweight materials, since extra weight reduces fuel economy.

  • Cover up. Adding a tonneau cover to a pickup truck can improve fuel economy by as much as a half-mile per gallon.

  • Choose wisely. If you’re towing a trailer, one with an angled front end will use less fuel than one with a flat face that pushes against the wind.

  • Find a balance. A car that’s too aerodynamic may not have enough headroom or visibility.

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