GMC Sierra: Putting Truck Aerodynamics Myths to the Test
Extensive testing in the wind tunnel helped improve the Sierra pickup’s aerodynamics – and, along the way, dispel a few myths about pickup trucks.
Full-size pickups have traditionally been known more for brawn than aerodynamic finesse, but GMC pulled out all the stops when developing the Sierra light duty truck.
To make aerodynamic advances to the vehicle, engineers examined every millimeter of the Sierra while in the wind tunnel. The 750-foot-long tunnel, through which a 43-foot diameter fan blows, can generate winds up to 138 mph.
Time in the tunnel and attention to detail led to design changes that both benefit fuel efficiency and improve interior quietness and refinement. The engineers also debunked some popular myths along the way.
“We can’t stop air; we can only guide it through the path of least resistance. It’s like electricity, without the shock,” said Diane Bloch, GM aerodynamic performance engineer. “The biggest misconception is that it’s all about single components. But a certain side mirror design doesn’t create a certain amount of drag, its interaction with the rest of the vehicle does.”
Illustrating the team’s attention to detail on all components of the vehicle, even the top of the Sierra’s tailgate and the center high-mounted stop light are optimized to guide air cleanly around the truck. A new seal was also added between the cab and bed to restrict airflow after the team found it was one of the biggest aerodynamic issues.
A common myth with pickup trucks revolves around whether a lowered tailgate is better for aerodynamics. According to Bloch, a tailgate in the up position is more aerodynamically efficient. As air flows over the truck, it falls over the cab and pushes forward on the rear of the truck. With the tailgate down, the benefits of that airflow are diminished.
“Replacing the tailgate with an aftermarket net is worse than having no tailgate at all,” Bloch said. “Imagine dragging a solid object or a fishing net through water. The net is going to require more muscle.”
In addition to aftermarket nets, the pickup market has a great number of available aftermarket accessories that have varying impact on aerodynamics. The bad: add-ons like bug deflectors on the hood, wider tires or aftermarket bumpers can cause added noise and increased fuel consumption. The good: tonneau covers for the bed help smooth airflow over the truck and running boards can also help air flow smoothly down the truck’s sides.