If you own a pickup truck you’ve probably heard or read where certain parts of the truck hinder airflow and in turn hurt gas mileage.
Well GMC dispelled those myths through extensive wind tunnel testing on their 2014 Sierra pickups.
What are those myths? A long-disputed topic among truck owners is whether a tailgate in its raised or lowered position is better for aerodynamics. Diane Bloch, an aerodynamic engineer at GMC trucks says despite what you think, 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,” says Bloch.
“Replacing the tailgate, she continues, with an aftermarket net is worse than having no tailgate at all. Imagine dragging a solid object and a fishing net through water. The net is going to require more muscle.”
So what accessories can truck owners add to help aerodynamics?
“Tonneau covers for the bed help smooth airflow over the truck. 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 trucks’ sides,” opines Bloch.
She goes on to say that round tube-style running boards can provide a minor improvement to the truck’s drag coefficient (it’s the measure of how air pushes on a vehicle as it moves) and fully integrated, flush mounted running boards, are even better.
The pickup market has a great number of available aftermarket accessories that owners attach to their trucks and those may have varying impact on aerodynamics, some of which owners would never think were obstructive to air flow.
“Add-ons like bug deflectors on the hood, wider tires or aftermarket bumpers can raise the drag coefficient,” contends Bloch. “The result: added noise and increased fuel consumption.”
Bloch bases these findings after studying the way air passes over, under and around the new Sierra pickup in GM’s state-of-the-art Aerodynamics Lab, a 750-foot-long tunnel through which a 43-foot diameter fan, powered by a DC electric motor and with the equivalent of 4,500 horsepower, can generate winds of up to 138 mph.
Says Bloch, “ We can’t stop air, only guide it through the path of least resistance. It’s like electricity, without the shock. And the biggest misconception is that it’s all about a single component. But a certain side mirror design doesn’t create a certain amount of drag, its interaction with the rest of the vehicle does.”
On the new Sierra, Bloch explained that the air dam on the truck’s front bumper 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 Sierra’s tailgate and center high-mounted stop light are optimized to guide air clearly around the truck.
“Because we detected unwanted airflow between the cab and bed, new sealing was added, says Bloch.
In conclusion, GM’s research and testing can make for good garage talk among truck guys who think otherwise.
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