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: Test to Determine the Relative Engine Load

Guess I'll go back to keeping the gate up.

Muser

 

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Running with the gate down can also vibrate your bed apart.

 

i would have liked to c the test done with the tailgate off, too.

 

if you're gonna drive with the tailgate down to save gas, why not take it off altogether and get rid of the extra weight

 

I used to drive with my tail gate down on my shortbed, there seemed to be less drag on the truck. It didnt feel as shaky as driving with the tailgate up at highway speeds. also when i had the tailgate up and opend both windows in the cab, then opened the sliding rear glass, tons of air would come in through that back window and all the leaves in the bed aswell, but when i put the tailgate down, that amount of air coming in through the back was reduced by quite a bit. i eventually just took the tailgate off for a few weeks. i didnt notice any signifigant increase in gas mileage though.

 

Before I sold my 01 V6 Ranger, I did the test twice. I made two trips to Tucson from San Diego. One trip gate down, the next up. Believe it or not, I the gate up averaged 1mpg better. Don't bother to put it down.

 

This is the exact reason why tailgate up is better for MPG then tailgate down. The swirling air in the back of the truck actually creates a high pressure system which acts as a deflector for the air moving across the truck. Notice how the leaves didn't fly right out, but instead they would float in the air then come down , then float and maybe escape once in a while? Well, the leaves are doing the same thing as the air around it. which means the air is in fact swirling and keeping any more air from entering the bed of the truck (because the incoming air from in front of the truck is at a lower pressure then the swirling air) subsequently keeping the air from hitting the tailgate causing drag. with the gate down, you are alowwing all of that if to escape and you lose the pressure system in the back of the truck, so now the air passing over the truck and bed, creates friction as it moves along. It is not a lot, but there is a small difference.

I know there was a wind tunnel test done on this, but I will have to find the website with that info on it.

Funny how what we think is common sense, is actually totally wrong.

Brad

 

Thats really interesting, i didnt know that it worked like that. id say the best thing to do is buy a toneau cover.

 

On long hauls I drive the tailgate off and install my ProNet,there is a difference in fuel mileage!1/8 tank on a 250km freeway drive!
Saigon

 

muser....welcome to the forum and great idea for the little tester you put together. I bet it would prove different mufflers on the same truck will produce different results. What year or type of vehicle would I look for to get a MAP unit? Again thanks for sharing.

Carl.....=o&o>.....

 

Informal tailgate test
<HR style="COLOR: #666666" SIZE=1>Here is an article from the scanguage website regarding the tailgate up/down question. Sorry about the length of the post here but apparently you can't post a link. Have a wonderful day.

Tailgate Up/Down and Gas Mileage - May 2004



With gasoline going ever higher in cost, I've noticed people putting more effort into
squeezing some extra miles out of a tank of gas. In particular I've noticed more and more
people in pickup trucks driving around with the tailgate down. I believe this is being
done with the belief that the air can flow easier through the bed of the truck and, with
less wind resistance, the gas mileage will go up.

This is a good theory. Without an easy way to measure it, it stays just a theory.

Another theory I have seen is that the mileage will be higher with the tailgate up
because air going over the cab creates a vacuum in the bed when the tail gate is up, causing
the air to go over the bed which reduces drag. What should I believe?

I recently got hold of a new device called a ScanGauge that can attach to the OBDII connector
in my truck and read out the gas mileage in realtime. Finally, a way to test the theory.

To get good scientific data, I needed to run the truck over a measured distance in as
close to identical conditions as possible, with one exception - once with the tailgate up
again with it down. To make the test even better, the test should be run in both directions
in order to cancel out terrain and wind effects. The test had to be done at a constant speed
within a few minutes of each other.

I chose a recently completed 6 lane freeway which still had very little traffic. The speed
limit was 65MPH. By traveling in the slow lane at 65MPH using the cruise control to keep the
speed a constant 65MPH, I was able to maintain this constant speed over a 5 mile coarse.

Before starting the test, I got the truck up to 65MPH and set the cruise control. I set the
ScanGauge in the CURRENT TRIP mode. This mode allows a reset to be done at any time so I could
accurately start the measurement when I passed a milepost. The fuel economy display showed
the average MPG starting from the time the RESET was pressed.

The test was started when I passed milepost 15 and completed at milepost 20. I then went
back the other direction pressing RESET at milepost 20 and noting the trip MPG at milepost 15.
The average of these two was taken for each condition, tailgate up, and tailgate down.

The results were surprising.

• TAILGATE UP = 17.6 MPG
• TAILGATE DOWN = 17.7 MPG

By surprising, I also mean disappointing.

Did the mileage go up with the tailgate down? Yes, but the amount is so small as to be
statistically insignificant. A single gust of wind during one of the 10 mile runs could account
for this much difference.

If someone out there has a removable bed cover, I would like to see this kind of test run
for it on and off. For someone with more ambition and one of those caps that blends into the
truck, this kind of test could be even more revealing. Does the cap help or hurt MPG?

For now I plan to keep the tailgate up. I feel more vulnerable with it down. I don't think
it would fare as well as the bumper if someone decides to see what happens when they run into the
back of a truck.

For more info (and more scientific data to sort through), the following conditions existed:

• Speed variation (from the ScanGauge) min=64, max=66
• Coolant temperature variation (from the ScanGauge) 198F to 204F
• Intake Air Temperature Variation (from the ScanGauge) 98F to 101F
• Outside air temperature (from the trucks outside temp) 92F.
• Vehicle: 2001 Ford F150 Extended Cab 4x4
• Vehicle Weight = approximately 5500 lbs
• Drivetrain: 5.4Liter V8 with 4 speed automatic

 

Studies have been done on this years ago. Drag increased by around .02cd with the gate down. Drag decreased around .03 with a cover on the bed.

I think UM did the study, but not sure.

 

I've been tempted to do this, but I wonder if propping up a 4x8 sheet of plywood (cut to size of course) in the box flush up at the same level as the sides of the box as a quick-and-dirty tonneau cover would work almost as well as good as the real thing... If you need to put stuff in the box, just lay the sheet down on the floor of the box first. It serves as a bed floor protector too :-) Don't have to worry about taking off the tonneau and figuring out what to do with it. It couldn't cost more than $20 compared to $300+.

Driving around with the tailgate down just causes it to bounce all over the place. I'd think if it bounced enough, you'll eventually end up losing it or breaking those hanger cables first.

BTW, I question that scanguage test result. Measuring mpg over 10 miles is such a small statistical sample size I'd rule any perceived mpg gain or decrease as statistical error, especially if the resolution of his mpg meter is at best 0.1mpg!

 

There was a program on Mythbusters tonight on the tailgate debate. They found that running with the tailgate up gave better mileage. They had a number of interesting test methods.