Wind tunnel testing by GM proves which method provides better fuel economy

By TTM Staff

There's been a long debate over fuel economy performance when a pickup truck's tailgate is up or down. Most truck owners agree that when the tailgate is down, it provides better airflow over the cab and reduces drag in the bed. But a recent wind tunnel test by GMC, performend on the new 2014 Sierra, tells a different tail.
According to Diane Block, GMCs aerodynamic engineer, leaving the tailgate up is more efficient than having it in the lowered position. GMC tested all aspects of the truck's aerodynamics for improved airflow and overall fuel efficiency. According to Block, the when driving with the tailgate up, the air flowing over the cab tends to fall down and then push forward against the truck, amost propelling it from behind. When the tailgate is lowered, the air escapes and doesn't add any benefit to the vehicle at all. In general, GM found that trucks get better fuel economy with the tailgate up.
While it may seem like GMC's testing shows an open bed with a closed tailgate, there are other facts to consider. The major one that has been overlooked, is that the testing was done in a 750-foot long wind tunnel with a fan that generates winds up to 138 mph. GM did not disclose or provide any indication of the wind speeds in which the 2014 GMC Sierra was tested.
Bloch also advised against nets covering the back of the truck. "Replacing the tailgate with an aftermarket net is worse than having no tailgate at all," Bloch said in a statement. "Imagine dragging a solid object and a fishing net through water. The net is going to require more muscle."
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