GMC pickups 101: Bustin myths of truck aerodynamics

The all-new 2014 Sierra full-size pickup truck spent more development time in a wind tunnel than any GMC pickup before it, resulting in design changes that benefit Hickory area drivers in both fuel efficiency and interior quietness.

To achieve improved airflow, aerodynamic engineers examined every millimeter of the truck to find areas of improvement, debunking some popular myths along the way.

To study the way air passes over, under and around the Sierra, engineers used General Motors’ state-of-the-art Aerodynamics Lab, a 750-foot-long tunnel through which a 43-foot-diameter fan powered by a DC electric motor with the equivalent of 4,500 horsepower can generate winds of up to 138 mph.
The engineers at GMC are always looking for ways to improve the vehicles our customers love. Their aerodynamic advancements are just one reason why the 2014 Sierra will be the most fuel-efficient V-8 pickup in the Everett Chevrolet Buick GMC showroom.

A new air dam below the 2014 Sierra’s front bumper successfully reduces drag because it directs air toward the ground and away from the truck’s rough underbody. And Sierra’s ducted flow path between the grille and radiator prevents air from swirling inside the truck’s front cavities.

Even the top of the Sierra’s tailgate and the center high-mounted stop light are optimized to guide air cleanly around the truck. And because engineers detected unwanted airflow between the cab and bed, new sealing has been added.

The pickup market has a great number of available aftermarket accessories, and GM engineers say those have varying impact on aerodynamics. Add-ons like bug deflectors on the hood, wider tires or aftermarket bumpers can raise the drag coefficient, which is the measure of how air pushes on a vehicle as it moves down the road. The result: added noise and increased fuel consumption.

A long-disputed topic among truck owners is whether a tailgate raised or lowered is better for aerodynamics, but engineers say 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.

So what accessories can Hickory, NC area truck owners add to help aerodynamics? Tonneau covers for the bed help smooth airflow over the truck, and engineers say soft covers are more beneficial than hard covers because they form to how the air wants to flow. Running boards can also help air flow smoothly down the truck’s sides.