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Author Topic: Tailgate down = increased mileage?
snopes
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Comment: Is it true that driving a pickup truck with the tailgate either
off or down will increase gas milage ?

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Bug Muldoon
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From Cartalk (is that reliable ?) :

quote:
Dear Tom and Ray:

I'm an aerodynamics engineer. When I was in the U.S. Air Force a few years back, I worked with folks from the Lockheed low-speed wind tunnel. In the 1970s, aircraft production went into a slump, and Lockheed started looking for other customers for its wind-tunnel services. Prime candidates were the auto makers, and Lockheed was successful in convincing Ford, among others, that the wind tunnel would help them reduce drag and wind noise on their vehicles. Needless to say, in the past 15-20 years, Lockheed has learned a lot about car and truck aerodynamics. Anyway, they actually performed drag tests on pickups with the tailgate both up and down, and found that drag was actually LOWER with the tailgate CLOSED! This ran counter to their intuition (and yours). The reason is that a closed tailgate sets up a large "bubble" of stagnant air that slowly circulates around the bed of the truck (we aero types call this a "separated bubble"). When air approaches the truck, it "sees" the bubble as part of the truck. So to the air, the truck looks like it has a nice, flat covering over the bed, and the air doesn't "slam" into the vertical tailgate. If the tailgate is open, or replaced by one of those "air gate" nets, however, that nice, separate bubble in the truck bed does not form (it "bursts"). Then the air approaching the truck "sees" a truck with a flat bed on the back of a tall cab. This is a very nonaerodynamic shape with a very LARGE drag. So, believe it or not, it's best for gas mileage to keep the tailgate CLOSED. Hope this information is helpful. Ed Fitzgerald, Research Assistant, Dept. of Aero/Mechanical Engineering, U. of Notre Dame

Tom: Sounds pretty convincing, Ed. Thanks. We also heard from none other than Bob Stempel, the former GM president, who wrote us to say that aerodynamically it doesn't make that much difference. But, he says, a pickup truck is structurally much SAFER with the tailgate up.

Ray: So for that reason alone, we suggest you throw away those tailgate nets, folks. And as your flight attendant might say, please return your tailgate to the upright and locked position.



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Casey, making hot chocolate
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I call BS based on personal experience.

Back some years ago, Dad would drive to Erie, PA on business regularly. He was contractor at a hospital out there, so he drove his El Camino on the OH-PA Turnpike at least 6 times a week. He kept a log of this, and averaged an extra MPG with the tailgate down.

Considering it was the same highway, on the same times of day, with the same load, over several years, it's pretty scientifically sound.

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Island Manta
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One thing that leaving the tailgate down does is decrease the structural integrity of the bed. If it's left down all the time, then the sides will, after time, begin to lean in - because the truck bed is built to have the tailgate in place.

Stuff doesn't slide out with the gate up, either [Big Grin]

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STF
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I've heard both of these reasons before. All I know is that my grandfather lost his tailgate altogether because he got hit with it down.

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Avril
Happy Xmas (Warranty Is Over)


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Question: If you're so concerned about gas mileage, why are you driving a truck with nothing in it anyway? If you have nothing to haul (which the tailgate would keep in), drive a car. Then you'll really get better mileage per gallon.

Av "darn it, I'm being logical again" ril

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Wizard of Yendor
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There are good reasons to drive an empty pick-up. Like comming back from hauling something. I don't understand why someone would pick a truck as their vehicle of choice though.

The lady across the street is like that. She just bought a new one and I don't think she ever carried anything heavier than a 10 pound bag of kitty litter in the last one.

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STF
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quote:
Originally posted by Avril:
Question: If you're so concerned about gas mileage, why are you driving a truck with nothing in it anyway? If you have nothing to haul (which the tailgate would keep in), drive a car. Then you'll really get better mileage per gallon.

Av "darn it, I'm being logical again" ril

If you need to use one quite a bit you may not have another vehicle. I only have a truck at this moment. Someone needs one in the family and it's me. That's one reason. Even at that I don't have a problem with someone trying to make a fuel inefficient vehicle a little more efficient.

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ilwrath
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quote:
drove his El Camino on the OH-PA Turnpike at least 6 times a week. He kept a log of this, and averaged an extra MPG with the tailgate down.
But it's tough to consider an El-Camino a truck. It has a car body and frame, along with aerodyanmic side panels. The ratio of cab height vs. tailgate height on the El-Camino is also much smaller than you'd find on most other vehicles that fit in a "truck" classification.

So, from that viewpoint, if the above "air bubble" description that Bug Muldoon posted is currect, it's very possible that an El-Camino would be an exception to that rule. Due to it's strange shape, it may experience a gain, while other more traditionally truck-shaped vehicles (say a Ford F150 or Chevy 1500) experience a loss with the tailgate open.

Removing the tailgate introduces another variable, as well. The vehicle is suddenly about 100lbs lighter. THAT may also have nearly as much impact as the aerodyamics do.

Also, I've heard that Tonneau covers help improve fuel economy. But from the "Air Bubble" description, it would seem that they may also harm things?

I think we need a Mythbusters semi-scientific test on this. [lol]

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Jason Threadslayer
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quote:
Originally posted by Avril:
Question: If you're so concerned about gas mileage, why are you driving a truck with nothing in it anyway? If you have nothing to haul (which the tailgate would keep in), drive a car. Then you'll really get better mileage per gallon.

Some people aren't wealthy enough to afford a vehicle for every situation.

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Casey, making hot chocolate
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quote:
Originally posted by ilwrath:
I think we need a Mythbusters semi-scientific test on this. [lol]

OK, I'll bite. I'll rent a pickup, and drive out West to see some Snopesters. Going out, tailgate down. Back, tailgate up. Bets, anyone? [Smile]

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Rick Maize
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Having grown up in Missouri and Kansas, I see this all the time. I am sure these drivers believe they are getting better gas mileage, they also believe whatever they toss into the bed of the truck will stay there without being tied in.
I've heard 'em say " It ain't goin nowhere" more times than I can remember. I have seen several older pickups with no tailgate at all, the sides of the bed basically flap in the breeze after years of enduring that lack of structural support provided by the closed tailgate. As to actual gas saving, if you are getting 12 mpg, going up to 13 isn't going to make a big difference. CLOSE THE DAMN TAILGATE . ( before I run into it while yaking on my cellphone and drinking my Starbucks coffee).

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Rick Maize
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Sorry I forgot to think of this in my other post,
but I would bet lunch money that if you drove across Kansas , then back, the difference in gas milage would be greater from the blowing wind than the wind against a closed or opened tailgate.

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ilwrath
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quote:
but I would bet lunch money that if you drove across Kansas , then back, the difference in gas milage would be greater from the blowing wind than the wind against a closed or opened tailgate.
Yeah, couple the wind with the differing altitudes of Kansas and Ohio, (especially if you are travelling to the west side of Kansas) along with the different traffic patterns travelling in each direction and the differing engine load profiles caused by all of these factors... The likelihood of getting any useful information from the trip drops to near zero.

Unless, of course, you were to stop somewhere along the way and visit someone who has a wind-tunnel. [Wink]

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ilwrath
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Well, I can't leave well enough alone. And I faintly remembered reading an article a while back and decided to hit google some more. Here we go. Some pretty strong sources for the "air bubble" theory. (As well as my thought that Tonneau covers create improvements.)

The "smoking gun" Fluent (CFD) model showing the air bubble can be found here.

Also, a Ford engineer speaks out.

quote:
"Putting the tailgate in the down position tends to increase turbulence and drag of the open box," explained Jack Williams, of Ford Aero Systems Engineering. "We've seen drag increase as much as .5 to 1 percent. Flow-through, web-like fabric replacement tailgates tend to increase drag even more; we've seen increases as much as 4 to 5 percent." In a nutshell, all of that extra drag translates into worse fuel economy for the vehicle.
I think we can mark the "tailgate down" rumor as false.
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RangerDog
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All I know is that last week, as an experiment, I came to and from work and drove everywhere with thw tailgate down. I got ~320 miles to the tank. The normal average for me is ~300. YMMV (Hehe). I think I might switch fillups back and forth to validate.

Ranger "Got an eight foot bed that never has to be made" Dog

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Delta-V
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quote:
Originally posted by Jason Threadshochet:
quote:
Originally posted by Avril:
Question: If you're so concerned about gas mileage, why are you driving a truck with nothing in it anyway? If you have nothing to haul (which the tailgate would keep in), drive a car. Then you'll really get better mileage per gallon.

Some people aren't wealthy enough to afford a vehicle for every situation.
A buddy of mine has a Ford F-250 with the V-10 motor. We did the math one day, and determined it would have been cheaper to make payments on a used Honda and drive it to work instead of the truck. He had about a 40mi commute of mostly highway, getting 12mpg. A Civic (he'd owned one previous to the truck) would get over 30mph on the same commute.

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"My neighbor asked why anyone would need a car that can go 190 mph. If the answer isn't obvious, and explaination won't help." - Csabe Csere

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abby 68
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So when i move to the country & the winter weather is bad enough to buy a pickup (for the 4 wheel drive) I should use a bed(tonneau) cover? [Confused]
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lawguy
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Are we interested in anecdotes and speculation, or controlled studies?

If science means anything, look here. It used wind tunnel testing of aerodynamic drag.

" Investigators at the National Research Council of Canada have determined that pickup truck aerodynamics is generally degraded — not improved — by the often-seen practice of lowering or removing the tailgate. Drag is generally greater and, to the detriment of yaw stability, rear lift can be increased by as much as 60 percent. Popular mesh tailgates worsen aerodynamics of these vehicles as well."

- as with everything, though, there are exceptions.

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abby 68
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quote:
Originally posted by lawguy:
Are we interested in anecdotes and speculation, or controlled studies?

If science means anything, look here. It used wind tunnel testing of aerodynamic drag.

" Investigators at the National Research Council of Canada have determined that pickup truck aerodynamics is generally degraded — not improved — by the often-seen practice of lowering or removing the tailgate. Drag is generally greater and, to the detriment of yaw stability, rear lift can be increased by as much as 60 percent. Popular mesh tailgates worsen aerodynamics of these vehicles as well."

- as with everything, though, there are exceptions.

ok one last question should the tailgate be up or down ? Just making sure

(keyboad $tuck BTW, fixed it [Big Grin] )

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Delta-V
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quote:
Originally posted by kita:
So when i move to the country & the winter weather is bad enough to buy a pickup (for the 4 wheel drive) I should use a bed(tonneau) cover? [Confused]

No, you should buy a Subaru, not a truck. Typical truck 4WD systems are pretty primitive compared to the newer car AWD systems. Most truck systems are RWD until you lock them into 4WD, and even then they only recommend 4WD mode for getting unstuck, not for driving. Add the fact that a truck's weight bias is very front-heavy, so you'll end up putting a couple of hundred pounds of ballast in the bed...otherwise you'll mostly be driving a RWD vehicle with very little weight on the drive wheels...not a good thing. Alot of the newer AWD cars have some sort of active handling system as well...most trucks don't.

An AWD car is definitely a better choice for winter driving unless you typically get more unplowed snow than a car can manage, tho Subaru's typically have pretty generous ground clearance. Even then, you're better off with a SUV with one of the more sophisticated AWD systems than with a pickup.

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Rick Maize
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Or a Subaru truck, after reading the Rodent Track article, I can now justify buying a cover for the bed of our BAJA, that is my only complaint about it, the suitcases get wet in the bed everytime it rain, and thinks are to easily grabbed from the open bed. Now just have to decide hard or soft cover.
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abby 68
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Subaru sounds cool. [Big Grin]


But as said I'll have to find out how well the area is plowed during winter, spent many summers in the area I'm moving to, but never been there in winter.

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AnglsWeHvHrdOnHiRdr
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quote:
Originally posted by Rick Maize:
Or a Subaru truck, after reading the Rodent Track article, I can now justify buying a cover for the bed of our BAJA, that is my only complaint about it, the suitcases get wet in the bed everytime it rain, and thinks are to easily grabbed from the open bed. Now just have to decide hard or soft cover.

FYI, this is the final model year for Bajas.

My hub has one, and we love it. 'Specially because it's safety yellow.

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RoofingGuy
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You kind of have to go with the wind tunnel tests and aerodynamicists on this one... there are too many variables involved in just driving the same route twice, once with it up and once down, to test it on your own. You could be driving into the wind with it up, and then be driving with the wind and/or following in the wake of a semi the second time around. Even with it up both times, or down both times, you could get widely varying results testing it yourself. I've had *double* the mileage out of the same amount of gas, over the same roads, in the same car, but on different days with differing conditions.

Around here, the pick-up drivers use drag/mileage as an excuse to drive with it down, but it's usually really just so that the tailgate blocks their rear plate from the cameras for the electronic toll collection.

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snopes
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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.

http://trucktrend.com/features/consumer/163_0506_ww/

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Bozone
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quote:
Originally posted by Delta-V:
A buddy of mine has a Ford F-250 with the V-10 motor. We did the math one day, and determined it would have been cheaper to make payments on a used Honda and drive it to work instead of the truck. He had about a 40mi commute of mostly highway, getting 12mpg. A Civic (he'd owned one previous to the truck) would get over 30mph on the same commute.

You also have to add taxes, registration, insurance, etc.
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