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Tailgate Air Resistance

fish6fish6 Member Posts: 50
edited February 2014 in General
Can anyone really tell me if the tailgate is truly
responsible for lowering fuel mileage? Some say
yes.Some say no, because of some air bubble that
circulates around not letting air to hit the
tailgate?????? Has anyone seen or use a device I
saw on some web site once that angles down from the
top of the tailgate at about a 45 degree angle
towards the box which allows air to flow over the
tailgate, rather than hit it squarely?


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    stanfordstanford Member Posts: 606
    Actually, you will generally get better mileage with the tailgate up. This causes a mass of 'dead air' to accumulate in the bed, which acts somewhat as a buffer in the same manner that a hard tonneau cover does. Lowering the tailgate really messes up your aerodynamics.

    Most folk who have tested with the tailgate up and down have, quite frankly, not done very scientific testing. The folks at Science News and a couple of other periodicals have all found that you will get better mileage with the tailgate up, all other things being equal.

    Note: this does not take into effect the weight savings from eliminating the tailgate altogether, although I doubt it would make much of a difference.
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    stanfordstanford Member Posts: 606
    Oh -- and the air does not really hit the tailgate while you're moving due to the dead air patch (in the same way that dust accumulates on ceiling fan blades). I have my suspicions that the 45deg block is merely an expensive gimmick of little or no value, besides getting in the way when you wish to use your truck.
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    fish6fish6 Member Posts: 50
    stanford...Thanks for the info.....makes sense!
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    cobra4cobra4 Member Posts: 6

    Back in the 1980's one of the magazines ran a test
    (Pop science? Pop Mech?) and claimed on an S-10 pickup that you got 1 mpg better with the tailgate
    DOWN than with it UP. That is the opposite of
    what stanford's articles said-anyone have anymore input?
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    stevekstevek Member Posts: 362
    On my '97 Chevy K1500 shortbed I have a soft cover. At highway speeds the front (toward the cab) cover bubles up and the part just before the talgate is pressed down (so much that I put a piece of wood under it). So I think the air would hit the talgate, therefore increasing drag and reducing milage. So much for scientific observations.
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    KCRamKCRam Member Posts: 3,516
    cobra and steve,

    Don't forget, a truck is designed and wind-tested with its windows shut and the tailgate up (closed).

    Steve, you are correct that some air hits the tailgate, but that is what creates the air bubble in the bed. Picture two airflow lines going over your truck, one about six inches higher than the other. The lower air line goes over the roof, into the bed, hits the tailgate and doubles back towards the cab. The higher air line must now flow over this retreating air in the bed, and clears the tailgate to get past it. In simpler terms, the air that hits the tailgate forms the bubble, allowing the rest of the air to go past the truck. If you left the tailgate down, two things occur that will disturb the airflow: the additional drop in height (an additonal 18-20 inches), combined with the funnelling effect of the bed sides. Air does not like to be channelled. Remember the top of your tailgate is pretty much in line with the base of the windshield, and air is coming around the cab as well as over it.
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    cdeancdean Member Posts: 1,110
    without getting complicated, a tailgate up causes a large flat surface which a low pressure pocket of air forms (directly behind the tailgate). this is pressure drag. with the tailgate down, that area is not there, and the pressure drag is gone.

    you still get pressure drag due to the cab, but not as much, because there is smaller area of your back window, AND, the presence of the sides of the bed cause turbulent flow. turbulent flow actually causes the "streamlines" Kcram mentioned to flow closer together, and reduce the low pressure wake areas that cause drag. (so much for not getting complicated)

    i haven't run a scientific study, but i ran a couple of tanks with the tailgate down, and got slightly better mileage.
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    markbuckmarkbuck Member Posts: 1,021
    I vaguely remember watching a program on the new NASCAR truck series dealing with whether or not they should allow or want to race the trucks with out tailgates....
    Recollection was that there were slight increases in top speed and reduced lap times without the tailgate at some tracks, but at others running with the tailgate up was an improvement.
    I am certain that I read another article that stated that the worst mileage comparing tailgate, no tailgate, and a 'prerunner' net was that the net was the worst case. I always run my trucks with the tailgate on and closed. I do tend to get better economy with the bed fully loaded with light stuff.
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    mharde2mharde2 Member Posts: 278
    Ford F150 owners manual says that driving with the tailgate down would adversely affect your mileage....I tried it all different ways, open closed, w/airgate, and it didn't make any difference that I could tell. IMHO don't worry about it. You will save only a couple of bucks a year in any event.
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    slw14slw14 Member Posts: 5
    Ford is petitioning the EPA to increase the gas mileage 1 mpg on their 99 F-150 that has the new factory installed soft cover. Ford studies show a .3 mpg increase in the EPA city cycle and 1 MPG on the highway cycle.
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    mbluemblue Member Posts: 1
    I have read a response to this question from the president of Ford Motor Company. Fords position on this is that the structural integrity of the truck is compromised with the tail gate down or removed. What little, if any, fuel savings that can be attributed to lowering of the rear gate becomes insignificant in the case of an accident.
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    corvettecorvette Member Posts: 10,407
    When my '96 Sonoma got hit in the side, the tailgate fell off. Go figure.
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    ricksterqricksterq Member Posts: 45
    Isn't driving with the tailgate down illegal?
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    raguragu Member Posts: 3
    My observation on tailgate up/down is as follows.
    Driving in Florida on flat land in a 220 mile drive I got 17.8 miles to the gallon with the tailgate down. On my return trip same miles with the tailgate up I got 15.6 miles to the gallon. I have a 5.4 liter w/3.55 limited slip rear and overdrive transmission. I drive a F150 Lariat extended cab. The AC was always on and the windows were closed. My trip speed was between 80-90 mph. I do prefer driving with the tailgate up tho due to the structual integrity. Got lots of looks as I passed others in smaller trucks by. Also I used my cruise control as much as possible. My escort radar detector was also on :) Can't wait to go back to Daytona Beach again.
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    raguragu Member Posts: 3
    Sorry I failed to mention my truck is a 99.
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    RichRich Member Posts: 128
    Some years ago, I had to move a mattress and box sprint set. Both brand new and in their plastic bag covering and laying flat in the bed of the truck. The truck was an '86 F-250 regular cab. When going up the freeway at 65-70, towards the cab of the truck the plastic bag was inflated and expanded as much as 12 inches. At about the center line of the rear wheels and rearward, the plastic bag was compressed flat onto the mattress.

    Based upon these observations there is a significant air pressure differential between the front and rear of the truck bed.

    On the '92 F250, I was never been able to notice a difference in the mileage between tail gate up or down. The diesel have so much torque that the tail gate resistance is not noticeable to MY right foot. On other trucks that are lighter and with an engine with less torque there may be a benefit to the tail gate in the down position.

    I do remember in either the '86 or '92 owner's manual, Ford stating that the tail gate is a structural member of the truck. (Or some such words.)

    Finally, yes it is legal to run a truck with the tail gate down. The states where I've lived and can remember the specifics of the law, it is a requirement that anything that extends 36" beyond the rear of the vehicle must have a red flag attached. The tail gate on most trucks is not 36" high. Therefore the tail gate can not extend into the area where a red flag is required.

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    cobra98cobra98 Member Posts: 76
    My '85 F150 4x4 gets ALWAYS runs out of gas at 209 miles (give or take 0.6 miles). I've been testing my fuel mileage by alternating a few tanks with and a few tanks without the tailgate for about 6 months now. Without the tailgate, I've been consistently getting an additional 19 miles out of a tank. That's been a 1mpg gain for me.

    Of course, that's my testing, your mileage may vary ;-)
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    stanfordstanford Member Posts: 606
    One thing to watch for -- I've heard of people given tickets for driving with their tailgate down not for length reasons (although making your vehicle longer than it seems might be annoying if someone pulls up close to you at a red light) but because it can obscure the license plate, which most certainly is illegal.
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    cobra98cobra98 Member Posts: 76
    Actually, I should clarify that when I talk about the difference with/without a tailgate, I don't leave mine 'down', but rather take it off completely.
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    JTOJTO Member Posts: 28
    I wouldn't drive with it down! Not because of covering the plate.... because I watched one unhook after some poor sap went over a bump!! It only has to swing up about 45 degrees for most tailgates to come off!
This discussion has been closed.