Automakers understand that aerodynamics significantly affects fuel economy and range. Design a vehicle that moves through the air effortlessly, and the powertrain (gasoline or electric) won’t have to work as hard. While designers of cars, crossovers, and SUVs have found countless ways to fool the wind and reduce vehicle drag coefficients (a lower figure is better), the traditional pickup truck segment still faces a challenge aerodynamic with its Achilles heel: the open body.

A popular accessory with pickup truck owners is the tonneau cover, a soft or hard panel that covers the cargo bed from edge to edge. Many truck owners purchase a tonneau cover to prevent loose items from flying off their pickup bed, to keep valuable items out of sight, or to improve the appearance of their vehicle. But there may be a fourth reason to buy a tonneau cover: to improve fuel economy.

Pickup trucks have terrible drag coefficients. Blame it on their massive size, their raised ride height, their giant tires, their colossal grille, their high windshields and their large towing mirrors. And to make matters worse, they have an open cargo bed. The gasoline-powered Ford F-150, the best-selling vehicle in North America, has a coefficient of drag (Cd.) of 0.463. The Ford Lightning, its purely electric counterpart, has an estimated Cd. of 0.44 (not much better). To demonstrate how dismal the pickup truck numbers are, consider that the Kia Telluride crossover is CD-equipped. of 0.34 or that the Hyundai Elantra sedan gains a Cd. of 0.29. The best-selling Tesla Model 3 electric sedan is equipped with a hot knife CD. of just .219, helping it travel over 350 miles per charge.

Some pickup truck owners have noticed improvements in their fuel economy by adding a tonneau cover. In theory, the air circulating on the truck circulates more easily because it is not trapped by the walls of the bed: there is less turbulence, therefore lower drag. But other owners reported little or no improvement. There are many different trucks on the market, in countless configurations, so no official scientific studies exist. (The show Mythbusters studied the theory in a few episodes, but their results were inconclusive because their speeds were too low.)

I recently ordered a tonneau cover for my RAM TRX from Just bolt-on performance partsan online retailer specializing in aftermarket performance parts and accessories. I wanted a versatile cover that would allow me to use almost the entire 5’7″ bed of the truck, so I chose a BAKFlip MX4 Tonneau Cover, a premium sectional hardcover with a weather-resistant seal The TRX is designed for extreme-road use, with flared fenders and oversized tires that catch wind and increase drag. As expected, it has a dismal 0.489 Cd – they don’t get much worse. .

Before the tonneau cover, my average fuel mileage around town (with lots of stopping and going) was 8-9 mpg. It averaged between 11 and 12 mpg on the highway, which is expected with a supercharged V8 under the hood. With the tonneau cover installed, my city fuel consumption remained unchanged. However, my fuel consumption increased significantly on the highway.

Thanks to the improved aerodynamics of a covered bed, I now notice 12.5-13 mpg on the open road. On a recent round trip from home to LAX, I noted 13.4 mpg on the 100.5-mile trip (including stop-and-go traffic around the airport). On a second trip to the San Fernando Valley and back, I averaged 14.7 mpg on the 54.0-mile trip. The figures for subsequent trips were also in the same range. Overall, I estimate my highway fuel economy improved by almost 10% with the addition of a tonneau cover, which is significant.

Although my results on my RAM TRX were nothing short of spectacular, adding a tonneau cover does not automatically guarantee a big increase in fuel economy. In researching countless truck forums, I’ve discovered that the benefits of a tonneau cover seem random. On some trucks, like my RAM 1500 platform, they work well. On the midsize Toyota Tacoma, owners only see improvements from time to time. Determining whether or not a tonneau cover will make noticeable changes in fuel efficiency depends on each truck: results depend on the test vehicle’s particular aerodynamics, configuration and options. It’s also important to mention that a tonneau cover will not improve low-speed fuel economy in any vehicle. If any benefits occur, they will be at highway speeds above 65 mph, when aerodynamic forces are strongest.

My suggestion to pickup truck owners looking to improve their fuel economy is to do some research online. Search forums for tonneau cover articles to find a wealth of free information, including countless real-world tests from owners who have posted their results.

All bedspreads will do a great job keeping items in bed and out of the elements. I am delighted with my BAKFlip MX4 tonneau cover. Yet as an unexpected added benefit, I save fuel on the highway. On that note, if I were RAM, I would do a standard tonneau on the 2025 RAM RHO (nearly identical aerodynamics to the TRX) and send it back to the EPA for testing to increase its official fuel economy numbers.