The Great Tailgate Myth

Someone recently told me about a guy who puts his pickup's tailgate down to save gas. People who follow that practice point to improved fuel-economy figures as proof it helps. Although this may sound like common sense to some, it's a myth: Driving in a stock pickup with the tailgate dropped won't save gas.

We can't blame you for thinking that a flat wall of vertical steel at the back of your truck might present some additional drag, which could hurt fuel economy. However, a raised tailgate doesn't hurt aerodynamics; it helps.

In the old days of blunt-face pickups, most of the wind noise came from the front, but modern trucks draw more noise from wind around the mirrors and exhaust and road noise from behind. Air that circles the cab gets sucked into the bed where it forms a pocket and is for the most part removed from air that flows over the truck. If you've ever had a paper cup or leaves in the bed, as the truck's speed increases, they migrate into the forward corners of the bed and don't get pulled out over the tailgate.

I'm not an aerodynamicist, and I don't have access to the sophisticated equipment and extensive resources to prove this point about airflow, but places like the National Research Council Canada, Ford Motor Company, and DaimlerChrysler do, and they've all come to the same conclusion: Driving with the tailgate down decreases highway fuel economy, and removing the tailgate usually makes it worse. In many instances, it also increases rear lift at speeds, an undesirable condition in a vehicle with only a third of its weight back there to start with.

Putting a tonneau or hard bed cover over your truck is the best thing you can do for highway fuel economy. A shell also can help. Since most of these are relatively light, the extra weight must be worth the improvement. This is one reason something like an Avalanche (which has a bed that's partially covered) often gets better highway mileage than an open pickup with the same drivetrain and tires--and weighs less.