Tail gate up or down?

Hi
Came across this web page on the effects of driving with the tail gate up or down, as well as having a camper shell on or off. I figured the
camper shell on was bad for mileage, but according to this site the most efficient way to travel is with the tail gate up.
Here's the link: http://hoist.hrtc.net/~wbt/f150_camper_shell_efficiency.htm
Guess I'll go back to keeping the gate up.
Muser
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A camper addition adds weight, so that will affect fuel consumption as will the profile of the unit.....kind of a no-brainer. As to that 'test'; lol, I'm positive they meant well, but.....
Tailgate up/down/off? Here in Texas, I've been told it is against the law to tool around with the thing down, probably the same in other states as well. Common sense should tell us that the tailgate in the up/closed position, and an open bed, will have air slamming against it. But the effect on fuel mileage is infinitesimal...IMO anyway. Take it off altogether....smooth airflow in that configuration!
Dave S(Texas)
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Just my 2 cents -- I gained 2 MPG by taking the tailgate OFF. -- pj
wrote:

A camper addition adds weight, so that will affect fuel consumption as will the profile of the unit.....kind of a no-brainer. As to that 'test'; lol, I'm positive they meant well, but.....
Tailgate up/down/off? Here in Texas, I've been told it is against the law to tool around with the thing down, probably the same in other states as well. Common sense should tell us that the tailgate in the up/closed position, and an open bed, will have air slamming against it. But the effect on fuel mileage is infinitesimal...IMO anyway. Take it off altogether....smooth airflow in that configuration!
Dave S(Texas)
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Actually there was a study done on this. Scientific research showed that tailgates UP provided less drag and smoother airflow...
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I always looked at the tailgate UP in the same frame of mind as a spoiler. It has to add drag, but on the other hand, it also adds downforce to the rearwheels. Not too important here in South Texas, but states that get snow, that extra downforce might be important tooling down the snow covered highway.

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wrote:

The bed gets "pressurized" at speed and airflow is actually smoother than with the gate down or removed. I saw somewhere on the web a few years back some fluid dynamics studies done on this subject. Can't recal where and a google seach nets me a big goose-egg..
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On Mon, 24 Oct 2005 21:35:36 -0700, The OTHER Kevin in San Diego <skiddz "AT" adelphia "DOT" net> wrote:

Google "Tailgate airflow study GM" and the first two hits give the following:
University of Michigan study here:
http://sitemaker.umich.edu/um.gm.truck/no_tailgate
<QUOTE> Aerodynamic Coefficients CD: 0.324 +/- 0.002 CL: -0.396 +/- 0.002
Results: The increase in drag caused by the removal of the tailgate was unexpected and seems counterintuitive. We believe when the tailgate is in the upright position, there is a ?bubble? of slowly circulating air in the truck bed that forms a virtual ?bed cover? of air and keeps most of the airflow around the truck from hitting the bed bottom and the inside of the tailgate. Removing the tailgate does not allow this bubble to form, which allows the faster moving air to interact aburptly with the bed bottom. This is very non-aerodynamic and causes the increase in drag. After testing was completed, we researched this phenomenon and found that results of a similar study confirm our hypothesis.
The top image is a picture of the truck with no tailgate. The graph below shows the convergence of the drag coefficient as Reynolds number is increased. <ENDQUOTE>
Here's one site that says GM did a study:
http://ths.gardenweb.com/forums/load/saving/msg1018054326731.html
<QUOTE> 9. Pickup truck drivers, don't lower the tailgate when driving on the highway. A GM study showed that this does not improve fuel economy, and can even make it worse. With the gate closed, air flows across the top of the bed and does not get "caught" by the tailgate. The airflow patterns are less efficient with the tailgate open or removed. Plus, running with the tailgate down can increase the likelihood and severity of a rear-end accident, since your tailgate will be extended behind your rear bumper. <ENDQUOTE>
OTOH, here's one that's trying to sell you something and says the opposite:
http://www.pace-edwards.com/gasmileage.asp
<QUOTE> At Western New England College , Todd Ortolani and Vanwijak Ewosakul, under the leadership of Dr. Alan Karplus, performed an in-depth study on the effect of airflow once it passes the trucks cab. The flow separates behind the cab and enters the truck bed resulting in a drag coefficient (Cd) of Cd = .432 if the bed is not covered. When a square truck cap is added, the drag coefficient increases to Cd =.480, or an 11.11% increase in drag. When a tonneau cover is used, the drag coefficient decreases to Cd =.381, or an 11.81% decrease in drag. Additional comparisons were made in the study by changing the tailgate. Replacing the tailgate with a cargo net resulted in Cd =.461, a 6.71% increase in drag compared to removing the tailgate which resulted in a C d=.447, a 3.47% increase in drag. Also, lowering the tailgate resulted in Cd =.414, a 4.17% decrease in drag. The results of this study concluded that the best method of decreasing the drag coefficient, thus increasing fuel economy, is to install a tonneau cover over the truck bed. <ENDQUOTE>
I'd believe the first two rather than the last one because of the bias of the sales pitch in the last one.
Greg
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Heh...Anybody who has watched a plastic grocery bag in the back go around in their rear view mirror for 20 miles could have told you that without a scientific study! ;)
Would be interesting to know about a tonneau cover....They would not have the weight of the cap and remove the bed & tailgate from the equation....
Scott

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says...

From: http://www.epinions.com/msg/show_~threads/cat_id_~3/id_ ~ 1893/forum_id_~124
Short version--
http://snipurl.com/j165
The truth About Truck Tailgates
According to a "Tech Tidbit" item in the September 2004 Road & Track magazine (page 156), it is generally better to keep your pickup truck tailgate up instead of down or removed. It seems counter intuitive, but research by the National Research Council of Canada determined that there was generally a lower drag coefficient (Cd) with the tailgate up than with the tailgate down or removed.
The difference wasn't big but it was measurable, with a 2002 Ford F150 Crew Cab measuring a Cd of 0.5304 with the tailgate up and 0.5425 with tailgate down. With the tailgate removed, the Cd was 0.5596. However, placing a tonneau cover on the bed lowered the Cd to 0.4967, probably enough to offset the weight of the tonneau cover if you do much highway driving.
Although not mentioned in this brief item in Road & Track, there's another good reason to have your tailgate up and latched: It adds to the structural strength of your vehicle.
--
I. Care
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The last link I gave closed with the following remark, but remember, this is the company that is trying to sell the tonneau covers in the first place:
<QUOTE> The results of this study concluded that the best method of decreasing the drag coefficient, thus increasing fuel economy, is to install a tonneau cover over the truck bed. <ENDQUOTE>
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Yikes.
If you are going fast enough to produce enough downforce to aid traction in snow, you are driving WAY to fast for snowy conditions.
I love it in Michigan after the first snowfall...about 5 spinouts per mile on the shoulder as you drive down the highway, covered in the blowoff from the snowplows. Most of those are SUV's driven by people who think that since they have 4 wheel drive they can go 70mph on an inch of snow.

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This issue was also the subject of one of the "Myth Busters" shows on cable TV. They had a scientific lab study the effects of the tailgate up and down with smoke tests, etc., and determined that, indeed, less drag and better mileage was obtained with the tailgate installed and in the up position.
Eisboch
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On Sat, 17 Dec 2005 00:52:37 GMT, "Eisboch"

That test was done with an extended cab - short bed combination. I suspect a standard cab with long bed would yield different results. As the smoke test illustrated, it depends upon the overall configuration of cab & bed.
James
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wrote:

Check this site for the University of Michigan using a GM truck model and Ford both saying Tailgate up is more efficient.
http://truckgadgets.com/tocfuelair.htm
Greg
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In the 80's some friends and I tested three different trucks. Two shortbeds and one longbed. One of the shortbed trucks had a toolbox mounted across the bed, just behind the cab.
Using very technical tufts of yarn taped all over the bed we found:
The LB had the least difference WRT tailgate position, the shortbed w/toolbox was almost identical, but the SB w/o the toolbox varied greatly.
bradtx
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snipped-for-privacy@aol.com says...

Here are some explanations for you:
http://www.cartalk.com/content/columns/Archive/1997/October/05.html
http://www.findarticles.com/p/articles/mi_qa3828/is_200405/ai_n9439015 Third para.
http://amos.indiana.edu/library/scripts/tailgate.html Simple explanation
http://snipurl.com/itsq Popular Mechanics
Hope that helps. I leave mine up because I don't want someone running into it, or me backing into someone either, why take the chance?
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snipped-for-privacy@webtv.net wrote:

Years ago when I used to use a P/U almost all the time, I found that the tailgate up would cost me 1 MPG or more on hiway
--

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www.thesnoman.com
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I. Care, Thanks for the info. I wonder how much more that imperical data gathering cost vs. 'borrowed' yarn and masking tape!
bradtx
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