Fact Check: Open your tailgate for better fuel economy?

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By Russ and Tiña De Maris

We recently got a “news item” from a Wyoming Dodge pickup dealer marked with the headline: “Removing a truck’s tailgate can boost fuel efficiency.” The balance of this news story was a set of instructions on how to remove the tailgate, and advice on not leaving the tailgate loose inside the pickup bed.

Kelvin Eng on wikimedia.org

Is there any truth to the idea that you’ll save fuel with the tailgate off the truck or simply left down? It’s been one of those “kick it around the campfire” issues for ages. The thinking of tailgate-less proponents is that the closed gate creates wind drag, thus reducing fuel efficiency. Consumer Reports put the idea to the test.

Using a 2013 Dodge Ram pickup equipped with a V8 powerplant, the good folks stuck on an inline fuel meter and ran the truck up and down the highway at 65 mph. With the tailgate up, fuel economy stood at 22.3 miles per gallon. Dropping the gate actually dropped the fuel economy to 21.5 miles per gallon, a 4 percent loss.

Interestingly, the CR team also checked for what difference the use of a tonneau cover would make. No tonneau, gate up: 22.3 mpg. Put on a soft tonneau cover, the mileage dropped dramatically to 21.4 mpg.

The fact that fuel economy drops when the tailgate does should not be a great surprise. Other testers have shown using wind-tunnel tests that wind-drag actually does increase with the tail gate down or taken off the vehicle.

##RVT838

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Derrek
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Derrek

Can someone explain why an empty truck bed, with the tailgate up, creates a ‘cushion of air’ effect which helps fuel economy compared to the tailgate down, but the tonneau cover has the opposite effect? Seems like it should create an even more efficient ‘cushion of air’ type effect?

Wolfe
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Wolfe

A teardrop is the ideal (simple) aerodynamic shape, and tailgate up acts like a lumpy teardrop, with the bed turbulence supporting and rolling the airstream more gradually over the cab/bed/off. The rolling air creates little drag because it’s NOT snagging on the tailgate like folks think. When you drop the gate, air sucks against the cab’s back like a flat backed van, creating great drag. The same happens when you “helpfully” add a bed boxcap…the tailgate and cap combo form a larger vacuum area than the sum of cab and raised tailgate. Although it looks funny and reduces cargo area,… Read more »

Mr Disaster
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Mr Disaster

I think Tim P hit upon a great idea. Fuel economy isn’t as much an issue unless towing. I’ve seen trucks with spoilers and any number of louvered or soft tailgate configurations. The results might actually provide useful info…

Jim Anderson
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Jim Anderson

Exactly right!,
The natural air bubble that is held in place by the tailgate creates less drag. Almost 30 years ago I saw pictures taken at Ford’s old proving ground near Kingman Arizona. Ford was trying out several different types of louvered tailgates in a pickup equipped with smoke generators. the pictures clearly showed the turbulence with the louvers compared to the smoother air flow with the standard tailgate.

tim P
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tim P

Has anyone ever tested this while pulling a fifth wheel coach? With the amount of vacuum created at the back of the bed under the fifth wheel it would seam that having an exit through the back without the solid tail gate would do something.

Les
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Les

I remember we covered this in my basic aerodynamics class in college working on aerospace engineering degree. If you think of air going over the truck as water coming out of a pipe you’ll see that with out the tailgate the wind is constantly “hitting” the truck bed and the rolling (friction) back along the bed and exiting out the end. With the tailgate once the truck gets going there is a cushion of air that builds up in the truck bed. This cushion of air then sits there in the bed, coupled with the boundry layer interaction of the… Read more »

Michael Bates
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Michael Bates

I observed approximately the same mileage loss in my 2011 F-250 with a 6.2 engine when I added a tonneau cover.

Ron Twellman
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Ron Twellman

Years ago the Mythbusters also tested and busted the tailgate question. I don’t think they tried a tonneau cover but they did try a mesh tailgate which didn’t help either.

Booneyrat
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Booneyrat

I lived in Wyoming for years,and the well known Wyoming wind does have an effect on fuel mileage,as well as altitude.I drove I-80 for awhile commuting from Laramie to Cody and back,going West on I-80 I would get 35 mpg in a VW Rabbit diesel,going East I would get 50 mpg..due to the tailwind…ask most truckers. As for tonneau covers,I beg to differ on the mpg as mine increased,same for using an aerodynamic shell. I really don’t buy the “drop the tailgate” scheme as I have tried it,didn’t make much difference.The biggest factor is a lead foot and vehicle weight.

Theo
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Theo

I believe that the MythBusters also ran a similar test which concurred with the CR testing.

Tommy Molnar
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Tommy Molnar

Not to mention how your “stuff” can fall out with the tailgate down – ha. This is why your truck HAS a tailgate!