Quick Install: Bed Covers Improve MPGs

Tonneau 4 II

Story and photos by G.R. Whale

If you don’t make a habit of hauling construction material, dirt bikes or other tall objects, a pickup truck bed cover makes a lot of sense. 

It adds secure storage and is weatherproof if you seal factory holes; it may look better than your beat-up truck bed and typically helps fuel economy. The extra 90 pounds isn’t felt much on a 5,000-pound truck, but better airflow helps on the highway. With a bed cover highway fuel-economy gains vary as widely as the number of variables, though it’s usually 8% or less (and much better than driving with the tailgate down). We had only two days for initial testing of this short-bed, regular-cab two-wheel-drive half-ton (5.3, six-speed auto, mild drop, slightly larger tires, odo-corrected) and commuting highway mileage went from a long-term 17.7 mpg to 19.1 mpg. 

Prices for the ARE LSX short-bed cover when installed are in the $1,300 to $1,400 range. If your truck gets 17 mpg highway and you bump that to 18 mpg, the payoff in fuel economy at $4 a gallon is about seven years; from 15 mpg to 16 mpg at the same price is 5.5 years. In either case, a secure bed that won’t fill with snow may be invaluable to you. 

The LSX cover has a six-layer construction, multiple adjustment points and a limited lifetime warranty. ARE covers are built-to-truck so you usually can’t buy one off the rack; the paint matches our 1-year-old GMC Sierra’s Summit White nicely, and options we passed on included lights, clothes rod and a wing.

ARE does only dealer-installs, which ensures a good fit for warranty protection. Based on previous positive experiences, we did ours at DACO in North Hills, Calif., in less than an hour despite strong thunderstorms. 

Tonneau 1 II
The spoiler/tailgate lip on some pickups, including our low-trim Sierra, has to be removed. Four screws and a firm yank did the job here. A replacement flush-fit plastic strip ($25-30) covers the big holes in the tailgate sheetmetal.

Tonneau 2 II
After fitting mounting brackets to the cover and exposing the foam tape, it is lifted onto the truck and centered. On the Sierra, the rear brackets use a toggle-nut in the stake pocket, but it’s not tightened until the side rail is clamped tight with locking pliers.

Tonneau 3 II
The forward brackets use L-clips to secure the cover to the bed rail, shimmed as needed. At this point, we found plenty of daylight at the leading edge of the bed. We sealed it with silicone to keep contaminants out. The final step is adjusting the lock rods for length and double-checking everything, including that keys work (they did). Locking requires just a one-eighth turn with spring-back to center. 


I had one of these on my old truck, it was a regular cab so I had to have some lockable storage, but with my extended cab I don't need it, I can store stuff in the back seat and keep the bed open to hualing.

The main point of the article is the fuel savings more than the lockable storage aspect; though I won't deny that factor as well. For you, Don, how about considering a different kind of tonneau that either folds or retracts to let you haul and fully covers the bed for aerodynamics when you aren't hauling?

While it's not the first thing on my list for restoring my '90 long bed, believe me, it is on my list. I'm estimating about 10 mpg on my truck as it sits, which makes my Wrangler look like an economy car by comparison.

Would never work for me as I am always hauling loads that are heavy and bulky or towing.

I have a crewcab. Seems to work better for me.

Wow, it takes 5-7 years to recoup the cost of these things? no thanks.... I don't need or want a cover bed, why compromise what you can haul in the bed by putting a cover on the bed? Unless I am hauling drywall in the rain, these items are pointless and expensive. For $2,000 I would rather add a supercharger and a cold air intake, or perhaps an airbag suspension or a dual catback exhaust.

Some things don't belong on a truck, and tonneau covers or cover beds are one of them.

GM actually did an extensive study on bed covers and found out that covering the back 1/3 of the bed yielded the best aerodynamics, and they averaged 1 to 1.5 mpg improvement in fuel mileage. I have ran a tonnaue cover for many years and have found it to be very true. On one truck I averaged 2mpg improvement in fuel mileage.

oxi can carry much more gear with a camper shell than a tiny toneau cover could handle...

It even acts as a de-facto storage shed...



@Allister: You do know you can get a tonneau cover for a lot less than $2k, don't you? They're just demonstrating one type that just happens to cost that much. You can find a retractible semi-rigid cover for a third that price.

i bought a tri-fold tonneau cover for $287.00 i love it can haul anything i want

i thought mythbusters said gas savings was untrue? or was it dropping the tail gate to reduce wind drag was a myth, i forget...lol

I personly choose the Back flip bed cover for the raptor, for a few reasons, it keeps my stuff from prying eyes and the elements, it gets old if you go shooting with friends or sking and dont want to leave your gear unsecured or have to put dirty gear in the cab if you stop for dinner or some thing. the advantage of the backflip and several other covers is that they fold out of the way, my cover can fold up against the cab if i need to put an oversized item in my bed and uses the lock on my tailgate so i dont need seperate keys and i can remove the cover in a few minutes without tools so very handy. Reaserch and find the cover that meet your needs (if you need one) I got mine for about $800 for a ford 5.5Ft bed and it hold up in the off roading.

I prefer the rollup cover, like Truxedo. They weigh less, there is no real difference in security (they're going to get in if they want to...) they're much cheaper, and they don't mark up the rim of the bed.

@Allistar Evans - coldd air intakes will give you a payback comparable to the cover. Cat Back exhausts are probably the same. Any modification to improve mpg do not yield huge gains. For most people they have to weigh other factors into the equation or chose accessories like the tonnneau cover more for securiy or aesthetics.
I personally prefer caps or canopies to tonneau covers. I have a dry box so that covers securing most items.
If one wants to save fuel, adjusting one's driving habits will yield the greatest dividends but are often the most difficult to change. I can easily save 10-15 % on my fuel bill by using hypermiling techniques.

@Lou: For an uncovered bed on a truck, the tonneau cover can still garner an additional 5-10% savings by flat eliminating the air circulation between the tailgate and the cab.

The difference between dropping the tailgate alone and a tonneau is two-fold. The tailgate acts as a kind of air scoop for the boundary-layer air which helps to develop an aerodynamic circulation that in turn forces most of the air the tailgate would normally catch up and over the tailgate. Dropping the tailgate thus creates a huge vacuum area right at the back of the cab rather than filling it with that 'airpool'. As Dean pointed out above, Mythbusters proved both in the water-tunnel and on the road that keeping the tailgate up definitely smoothed the air flow over the truck.

A tonneau cover however, allows the air to fall off the back of the truck in stages rather than creating one big hold behind it. Your cap or canopy does smooth the airflow around the truck, but now leaves this big hole again right behind the truck. Between the two, the step-down method makes two smaller holes and results again in a noticeable savings over not having a cover at all or having a big cap.

By combining those hypermiling techniques and the tonneau cover, you realize even more savings. Not that all that many drivers even attempt hypermiling.

I have a tonneau cover on my Isuzu. My wife wanted it and its ok but I could live without it. What I would really like is something like Oxi has but put a crescent moon on the rear window and a portable potty in the back. Just kidding. Too each his own.

I myself would like to see a cover shootout. I have less then $650 into my Backflip. I don't know how much it helps, but to test a bunch I would need to run same way same day with same wing a weather conditions. If it helps, great. If it doesn't much, oh well. I still have a fairly dry place to put stuff, it's out of sight, out of mind, and it's locked cause the locked tailgate. I have taken trips with car parts or military gear and don't like leaving it out in the open if I have to use a bathroom at some truck stop. The non folding ones are costly and say you buy something that won't fit, I see these people prop it up and stick a dryer in the bed or something like it. See how that works for mileage! The folding one works for over 90% of things, I just took it off to get the last 10% to move some stuff. The non folding ones have their place for some, just not for me. I would get a full size cab level topper but the manufactures are too proud of them.

Here's a picture of airflow in this post.


Mythbusters had said "dropping the tailgate did NOT improve gas mileage". In fact leaving tailgate up (as trucks were designed) the downforce of the wind does help handling.
Me, I installed a RETRACTS roll back bed cover (4 clamps) paid ~ $900. in '03. In summer or winter with snow ice, it still retracts. For occassional hauls, works for me plus it locks.

You can get a high quality roll up for less than 500 bucks, WITH a lifetime warranty. According to the math here, it'll pay itself off in less than a year. SOLD!

@Vulpine - years ago (dare I say decades) when tailgate nets were popular, I bought one. I found no difference in mpg, but as you pointed out, my truck was very tail end waggy. I prefer canopies over tonneau covers (no pun intended) because they provide considerably more dry usable space than a tonneau.

@Allistar you can do it, go install that super charger and cat back system and go scare the hell out of those teens in those imports with the soup cans on tha back.

I have had many pickups over the years and for most of them I installed a tonneau cover. Mu current ride a 07 Silverado 4x4 with a factory cover can get 23 mpg easy at 60 mph. Of course I also went with a Magna flow catback and cold air intake. So I have my cake and I'm eating my cake

Funny my 1/2 ton ext cab 4x4 with a 5.3 gets the same highway mpg as a Ford reg cab 2x4 V6 Eco.

But I will say do I really need that V8 if I never pull anything?

I don't believe that these covers really improve gas mileage. I've owned two in the past, one a fiberglass tonneau by ARE, and the other was a full sized shell camper made by LEER. They're built to look like they're part of your truck and are heavy. The full size shell took two people just to put on and remove. I'm not certain but I'm sure it weighed probably around 250-300 lbs. This added weight means your truck is hauling it. I thought I was getting mileage, but after a few years I decided to remove and closely watched my mileage. It improved drastically. The mileage saver is just marketing to try and get people to buy into these.

Wow Peter, it must have really helped you out, (the cover) PT.Com did the gas mileage test on the 30K shootout and the 5.3 wasn't that good in it. Must be extremely flat there to.

@ vulpine

thanks for the info, makes sense the way you stated it.

"They" say removing 100 pounds from a vehicle can save 2% in mpg. So if you add a 100+ pound fiberglass deck, how could that possibly save gas? I call B/S.

Maybe someday they will wind tunnel test various toppers of all kinks to figure what works best for certain combos. I actually wouldn't mind stepping up to a cap, one that is cab height or barely higher at the back. The hole in the air it punches would be good for me when hauling a car on a trailer. But it is said that the toppers that do best on mileage aren't the ones that get to the back of the truck and just drop straight, an angled one is better.

Here is wind tunnel test on tonnuea covers. http://www.tc-ol.com/pdf/SEMA_Gas%20Savings.pdf
Like I said earlier I got a 1.5-2 mpg increase after I installed my tonneau cover not a topper.

It would be interesting for PUTC to test a number of products that may improve mileage; toppers, tonneaus (rigid and flexible), tuning chips, etc. Although testing every product on every type of truck would be near impossible, testing a few products on one truck would provide some good information.

@Mad Max2 - weight is more of a hindrance in city driving or any stop and go situations. The laws of physics dictates that a heavier object will take more energy to move and to stop moving. Once the object is moving the extra weight of something like a tonneau cover isn't going to cause such a big difference in energy consumption. The extra energy to pull/push it up a hill will be offset by the extra stored energy as it comes down a hill. We've seen tiny gains in mpg at city speeds with trucks, but some impressive gains at highway speeds. Aerodynamics play a bigger role at highway speeds than weight.
Most of us do not buy these devices as a way to improve mpg. Security, aesthetics, convenience, performance gains etc usually carry more wieght (pardon the pun) than fuel economy.
I just read that in the USA an extra billion gallons of fuel per year is consumed due to obesity. I'd be more worried about that fact then the extra weight of a bed cover ;)

I live in the Pacific NW so not all flat. But I'm also doing my best at driving no rapid starts, etc, etc. But guessing that the cold air intake and catback have more to do with it then the cover.

Around town mpg sucks like 15-16.

Today I was in a tunnel and thought about just smashing it just to hear that catback, but sense took over. Of course at the end of the tunnel was a state trooper so very glad that sense took over.

A note for all truck owner... I bought my pickup used and it had E3 plugs in it. It would never get more then 18-19mpg highway. Had the dealer put in the correct OEM plugs and started getting 23mpg highway

Peter - nice to hear that you are getting good results with your modifications. I had read that one can gain 3-5 % with an air intake kit, cat backs have various claims as to mpg. Most seem to post HP gains only. I do agree that driving habits play a huge role. I've gotten a best of 20.4 mpg out of my 2010 Supercrew on the highway. (Stock truck) I'm usually in the 18 - 20 mpg range depending on weather, traffic, and cargo.

I'd like to try and clarify a few issues many of you are having, starting with the difference between a tonneau cover, a bare bed and a bed topper like a Leer or other camper box. I also want to point out the method the Mythbusters used to test their mileage for the tailgate story.

Basically we're looking at three different truck profiles which each has a significant affect on the airflow around them. We also have to consider the different bed lengths of some trucks because what might work smoothly for a short bed (see TRX4 Tom | Apr 30, 2012 3:50:26 PM above) might not work at all on a long bed. The page that Kirk above links shows you a bunch of charts, but don't really show you the airflow itself, only the relative drag numbers which may be confusing to some. Still, they do demonstrate the point in general.

Looking at TRX4's photograph, you can see that the air flow across the top of the truck just barely touches the top of the tailgate with that particular rig. Were the tailgate down, that falling air would hit the tailgate itself, working like a lever to push the nose of the truck into the air. As Lou pointed out, it made the truck feel "waggy" but instead of a tail wag, what he was getting was less weight on the steering tires which made the whole truck feel unstable. By the way, this was a very big problem with the '59 and '60 Chevy Impala because when you combined those wings (air pushing down on top) with that front bumper (pushing air down under the car) well, guess what? The nose wants to float.

The full shell such as what some of you have described have almost the opposite effect; the air goes up and over--then has to fill in that cavitation space behind the truck. They looked aerodynamic to a great extent, but you were just punching a big hole through the air and leaving a vacuum behind you--trying to drag you back again. Airplanes have a tapered tail for a reason, and that's to help the air wrap around the plane and reduce drag.

Now, before I go to the tonneau cover itself, you'll note that I emphasized TRX4's photo for the short bed. The reason for this, and what the Mythbusters were playing with, is that with a longer bed that tailgate actually does catch some of the air like a parachute. However, that air is forced to circulate forward against the back of the cab where it's driven upwards again--pushing against that boundary-layer air that originally got caught and now forcing it beyond the tailgate, effectively giving you an air-powered wing behind the cab.

Now, the tonneau cover allows the air to fill in behind the cab more smoothly, much as you see in TRX4's photo even with a long bed, eliminating that particular parachute effect while then allowing it to step down again behind the tailgate without having to buck that huge hole a cap would have caused. A functional example of this might be demonstrated by NASCAR's truck division where every truck has a flat bed at the top of the rails like a tonneau.

Even a fabric top can offer at least some measure of this effect as demonstrated by the drag coefficients shown in Kirk's link. When comparing baseline (tailgate up for each model tested) Tailgate down and tonneau (three models on some trucks) you can see that the tonneau greatly improved airflow even over the baseline for every single truck tested. This means that a tonneau will very clearly improve gas mileage for any truck while it's in place.

Now, whether you use a hard-shell fiberglass top or a fabric top, from this point on the overall weight of the top will have some effect as well. While one of you mentioned a cap weighing 250-300 pounds which will obviously be counter-productive, a heavy tonneau will also have some affect on the improvements. The top described in this article is 90 pounds overall while some of the other tops tested and discussed in this board could also have an effect based on its weight. Note that in the charts on Kirk's link that most tonneaus have minor differences in overall effect when compared to each other while offering significant improvement over baseline and tailgate down.

I have an 8-foot bed on my truck. Now just imagine what that will do at 80mph without a tonneau.

I forgot to mention the Mythbusters' testing method. With two identical trucks they filled them up at a gas station and drove them up to the freeway where they used 5-gallon cans to fill them all the way up to the gas caps--ensuring as equal amount of fuel in the tanks as possible. They then drove those trucks down the freeway until they completely ran out of fuel. The truck that ran tailgate-up went almost 10 miles farther on the same amount of gas. That may not seem like much, but it did demonstrate about a 2% difference. A tonneau should offer about 5%-10% in a similar test.

That's some really interesting information. So if I understand you correct, uncovered, a short bed truck will inherently get better mileage than a long bed (all else being equal)? Does the cab length (regular, extended, crew) have any effect?

if it isnt a GM product F OF_!!!!!!!!!!!!!!!!!!!!

That's a good question, Luke. I can only guess since I don't have a wind tunnel to verify it, but I'm guessing the length of the cab will only have minor effect on how quickly the air drops in behind it. If you note the charts in Kirk's link, the Chevy's tailgate-down numbers came in worse than the short-bed Ford F-150 but surprisingly performed worse to the long-bed Ford perhaps because the Chevy was a 4-door while the Fords appear in the photos to be extended-cab 2-doors. I couldn't tell what the RAM was but I think it, too, was an extended cab.

So based on that admittedly rough analysis, I can only say that I believe the longer length of the cab had a detrimental effect in the tailgate test while somehow performing better than the other three trucks with a tonneau cover over the bed.

Another item of note is that by brand there seems a visible oddity that may have to do with other aerodynamic features of the trucks. In looking at the average numbers with the different tonneaus we come up with:

Coefficient of Drag
Ford short bed: Roughly 0.97
Ford long bed: Roughly 0.95 (one cover managed 0.92)
Ram long bed: Roughly 0.95
Chevy long bed:Roughly 0.93 (two of three tonneaus near 0.92)

(Long bed = 6.5 feet)
(Short bed = 5.5 feet)

Make your own conclusions here but it seems to me that for whatever reason, while uncovered and tailgate down the Chevy came in last, when covered the Chevy came in best unless you can discover what that one specific cover was that got 0.92 on the Ford. So, was it the longer cab, or other aerodynamic factors in the design? Based on the discussion of the tests however, they normalized (balanced) the trucks so that only what was done to the beds changed any numbers.

@Vulpine - good posts. When I said the tail end was waggy on my 1990 F250 long box with a tailgate net was that it was really light in the rear. If the roads were wet or on gravel I could spin the tires real easy or it would slide sideways. i noticed that at highway speeds the rear end fealt loose. The problem went away with the tailgate back on.

@Peter: I was just up that way, the Pacific Northwest! Back in August. Drove up from Arkansas, went through Pendleton Or. and over to Portland, stayed in Olympia and watched figure 8 races in Monroe. Brought back and old figure car! LOL! Did my 2 years a Ft Lewis!

Definetly not flat. I wouldn't say I-5 is near as steep as the hills here in the Ozarks of northwest Arkansas or southwest Missouri. It's not Illinois either. Made my share of runs over the pass to Soap Lake. It is an awesome sight once you get north out of Seattle and all you see is mountains. Or Mt. Rainier!

The cat back and intake could be alot. I would like to see them dyno a truck at a show and stick a K&N or other one on and re-dyno. Then I might consider. Lots of $. I did the cat back (well, my version of it) on my 07 Dakota H.O. I had the 2" pipes right off the cats replaced with 2 1/4 to a flowmaster 2 into 1 and I think OEM was 2.5" single, I went 3" single to a Hooker Aerochamber muffler and no resonater. I really didn't feel much. Later when the engine came out for a new cam cause the original was scored, they stuck in JBA shortys, which seemed to do next to nothing and I didn't like them that well. Maybe I shoulda bought Gibsons for more $? The H.O. had bigger cams and I guess hardly ever had the issue I did. I later had the resonater stuck back on. 400 miles from NW Arkansas to Ashland Nebraska can be alot of drone.

I now just have a drop in K&N added 500 miles ago and I am not fixing anything not broken! I do think if Ram had better exhaust manifolds, they can get more power, and torque. But I'm just a wrench turner. If my tires were street orientated I would see maybe 1 MPG better. Have Good Year AT/S's. But then I can hold the load better and less worry of flats.

I purchased of of these bed covers and it seemed to help my gas mileage. http://www.roughcountry.com/exterior-parts/bed-covers.html

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