Do Tonneau Covers Improve Gas Mileage? Sometimes, and Not by Much

An open bed is a box with the wind spilling into it, so a lid ought to help. That idea has stuck around for years, and pickup aerodynamics doesn't cooperate with it. Air coming off the cab roof curls into the bed, and with the gate up it raises the pressure on the back of the cab. That's why the gate-up truck turns out to be the slippery one, and why a cover has less drag to remove than you'd guess.

We lean on published measurements here: road tests run with fuel meters or fixed loops, and wind-tunnel results reported by the engineers who ran them. Where a number is an engineer's estimate rather than a measurement, we label it. Owner fill-up stories carry the least weight of all.

What the road tests measured

Only a handful of published road tests put a cover on a pickup and logged the fuel. They don't agree, and the disagreement is the finding:

Consumer Reports ran the most careful of these, and its 2013 test found the cover hurt: 22.3 mpg fell to 21.4, a 0.9 mpg drop, slightly worse than the 0.8 mpg lost by dropping the gate. That was one truck, one speed and one cover, a factory soft one. TFL's 2022 loop went the other way, 1.61 mpg better with the cover, though TFL's write-up doesn't name the cover and reports a single run each way. TFL itself notes that temperature, wind and even humidity move the numbers, which is why its 2023 tailgate test ran a control loop first.

The 2006 numbers come from Bruce W. Smith's own fill-ups, published in Truck Test Digest and reprinted by Equipment World. They're the roughest method of the four, but they land between the other two: a gain of about 1 mpg at 70 mph.

What the wind tunnels say

Wind tunnels hold everything still except the thing being tested, which is why the engineering reports agree on direction where the road tests don't. They measure drag, though, not fuel, and the two aren't the same thing:

The Ford and Chrysler quotes come from the same Truck Test Digest article as the fill-ups above. GM's comments were reported by Equipment World during the 2014 trucks' development. The two SAE papers are summarized from their published abstracts: Cooper's and Texas Tech's.

Drag isn't mileage. Ford's engineer turned that 8 to 10 percent drag cut into an expected fuel gain of about 2 percent on the EPA city and highway cycle and about 5 percent at a steady highway cruise. Those are Ford's estimates, not a measured fuel test. They show the shape of the effect: most of a truck's fuel goes to things a cover doesn't touch, and the aero share shrinks as you slow down.

Here's our own arithmetic on Ford's estimates. Take a truck that averages 20 mpg on the highway. Over 1,000 highway miles it burns 50 gallons. At 5 percent better, 21 mpg, it burns about 47.6, a saving of roughly 2.4 gallons per 1,000 miles. At 2 percent better, 20.4 mpg, the saving is about 1 gallon. Either way, a cover pays for itself in fuel only over a very long time, and only if the gain is real on your truck.

Leave the tailgate up

The tailgate-down habit is the one myth every source here that tested it agrees on. Consumer Reports measured 22.3 mpg with the gate up and 21.5 with it down, a drop it called 4 percent. TFL's back-to-back loops went from 21.8 mpg to 20.15. Ford, Chrysler and GM engineers all reported more drag with the gate down, and the National Research Council paper adds a lift penalty on top.

The reason is the air off the cab. It spills over the roof and rolls into the bed, and with the gate up, Chrysler's aerodynamics supervisor explained, the pressure on the back of the cab rises and the drag falls. GM's engineers describe the same air pushing forward on the rear of the truck. Drop the gate and the benefit goes with it.

With a cover on, drive with the gate up too. TruXedo support has said not to drive with the gate down under a closed Sentry CT, and we'd follow that for any cover.

Net tailgates make it worse

Skip the mesh or net tailgate if mileage is why you're looking at one. Ford's engineer reported that flow-through mesh gates raised drag by as much as 4 to 5 percent, well beyond the 0.5 to 1 percent of lowering the stock gate. Chrysler's aerodynamics supervisor said mesh replacements make drag worse still, and GM's engineer went further: a net is worse than no tailgate at all, because the mesh adds resistance of its own.

None of the sources we cite measured a net's fuel use. The case against nets rests on engineers' wind-tunnel statements, and those all point the same way as the tailgate-down results. Keep the factory gate.

Does the cover style matter?

No published test we can read compares cover styles on the same truck, so we won't rank them for mileage. What the sources do say is mixed:

• Soft covers: GM's aerodynamicist said in 2013 that soft covers help more than hard ones because they take the shape the air wants. Yet the only road-tested cover we know to be soft, the factory cover on Consumer Reports' Ram, cost mileage.
• Hard covers: the 2006 Truck Test Digest article called a hard cover better than a soft one without publishing a head-to-head number. Ford's 8 to 10 percent drag figure doesn't say which style it was.
• Partial covers: Texas Tech's 1988 paper got its 5 to 6 percent drag cut from a cover over only the rear part of the bed, in its own wind-tunnel tests. Its abstract doesn't compare that with a full-length cover.
• Folded, rolled or retracted: an opened cover isn't covering the bed. No source we cite measured a folded stack at the cab or an open roll-up, so don't count on any gain with the cover open.

Low-profile against raised covers, flush rails against tall ones: nobody we can cite has measured it. A cover maker that claims one style saves more fuel should show you the test.

What moves your mileage more

If fuel is the goal, look at these before the bed. The figures are fueleconomy.gov's and the add-on list is GM's; the comparisons with a cover are ours:

• Speed. Gas mileage usually decreases rapidly above 50 mph, per fueleconomy.gov. Every road test above that states its speed ran at 65 to 75 mph, where aero matters most. A 2025 Silverado owner with a hard cover gets 21-22 mpg on cruise at 70 and 23-24 at 65, and averaged the same before the cover went on. Ford's estimate for the mixed EPA cycle was less than half its steady-cruise figure, so expect less in town.
• Cargo on the roof. A large, blunt rooftop cargo box can cut highway fuel economy by around 6 to 17 percent, and 10 to 25 percent at 65 to 75 mph, per the same site. That was measured on a small sedan and a standard SUV, not a pickup, but the top of that range is well beyond any cover result here, and it runs the wrong way. Rear-mount boxes cost much less.
• Weight. An extra 100 lb can cut mileage by about 1 percent, per fueleconomy.gov, with smaller vehicles hit harder than big ones. Peragon publishes 35 lb for the Landmark's panels on most trucks. Our own estimate from that rule of thumb puts that at about a third of a percent, before the rails, and less on a full-size truck. None of our three picks publishes a weight.
• Add-ons that disturb the air. GM's engineers said hood bug deflectors, wider tires and aftermarket bumpers can all increase drag and fuel consumption.

Why your own fill-ups can't settle it

Owners who post before-and-after numbers split roughly evenly between a gain and little or no change, and the gains run from about half an mpg to 4 mpg, the biggest after a single 60-mile drive. We believe they saw those numbers. A before-and-after at the pump still can't separate the cover from everything else that changed between tanks. The effect the engineers estimate is a few percent at most, and wind, temperature, speed and load can move a tank's numbers as much on their own. TFL's 2023 tailgate test opened with a control loop for exactly that reason.

If you want to check your own truck, borrow that method and repeat it: the same route, the same speed on cruise, the same day, cover on and cover off, back to back, on more than one day. Anything less tells you about the weather.

If you're buying a cover anyway

Buy a cover for what it does well, a drier bed and cargo that stays hidden and locked. All three below come from our full reviews, one per job, and the bottom row of the table carries each review's leak-risk reading. Our leaking tonneau cover guide covers where each style lets water in:

On most trucks the cover itself clamps on with no drilling, per each maker. Weight is the gap: none of the three prints one.

• For a dry bed, the Sentry CT. It's the only cover we've reviewed with a low leak-risk reading, and rolled up it leaves the rear window clear.
• For security, the LEER HF650M. Lock the tailgate and the cover stays shut, since the CYNC latch only releases with the gate down. It's cheaper than the CT on the matching listings. LEER says it won't work with RamBox or the multifunction tailgate.
• If fuel was the main reason you were shopping, the Tyger T3: spend the least. It costs far less than the other two, but it has no lock and takes no weight on top.

Weighing hard against soft for other reasons? Our hard vs soft guide goes through security, weather and price. Order by your exact truck and bed: each pick's fit rows list only Amazon listings whose product page we checked, and if your bed isn't there, check fit for your truck.