Found this on the**********.com, and it is very interesting.

http://sitemaker.umich.edu/um.gm.truck

Says a bedcover reduces drag by 22%...

wow -- so anticompetition with the *****'s....

Interesting, So leave the tail-gate up.?

Ben

Nothing new here. Chrysler did a test a few years ago and came up with the same data. The tailgate up works just as good with the 5th wheel on. I had to screw my rubber mat down back by the tailgate to keep it from smacking the bottom of the 5th wheel overhang. Later! Frank

Frank,

Did the rubber mat smack the 5er with the gate up or removed?

Thanks,

MaxRock

man Frank -- I wasn't claiming it was new...

Just confirming your data was accurate Seth. I used to take the tailgate off until I read the report on Dodge trucks. I have always run the tailgate up on my 02. Later! Frank

Was this information supplied along with the directions for installing your new Tonnue cover:D

With a cover you get 22% less drag but drop the tailgate which lets the air flow free same as a tonneu and get more drag...I guess the verticle bedrails cause a disturbance in the trucks coefficient of drag.... Also put a huge wing on the roof more crap in the wind for drag and pick up a good percentage too.....

I have done some expereminting on this in the past.....on a trip from Lynnwood, Wa to Elko, Nv last fall I tried a couple things.

- I filled up in Oregon and drove with the gate up untill the next fuel stop

- Put the tailgate down and drove to the next fuel stop.

Same type of driving same speeds and I got 2 more miles to the gallon with the tailgate down..by my hand written calculations?

So what the article is saying is with a tailgate up the wind pounding into it the opposite direction the truck is traveling and being pushed up under my toolbox this somehow makes my truck less drag efficient? Unless the air being pushed in a cyclone (sideways between the bedrails) is lifting the air off the cab and bypassing the bed and tailgate hmmmmm.....so why then would a tonnue cover help it just pushes the air off just like having the tailgate down.....unless it's like a jet ski with an extended ride plate then the extra 2 foot of tailgate is making too much resistence......but makes it ride nice with no porpusing?

I have heard this for ever... since before I started driving... seems really hard to swallow......someone did a study with the cargo net and tailgate and the tailgate won....guess that blows the tailgates at fault idea since there was no tailgate when the net was installed.... unless it was GM's study because they didn't want people taking off the tailgate cause then you would loose all that free advertisement.....might be on to something here...conspiricey theory anyone :ro)

I guess the mystery lies in the verticle bedrails we unlock their key and wow maybe we open the door to the universe..:eek:

I suppose my toolbox messes with the equation and the visor (it is a new style that lets the air pass through though) does mess with the airflow a bit on my example truck........but I still don't see how the air pushing down on the tonnue cover is any different than the air pushing down in the bed...guess thats why I am not an engineer?

I live by the simple words of my Grandpa... Believe only half of what you see part of what you read and none of what you hear....it's worked this long!

Just my .02

WileE1 -- read the explanation under the bed cover link. It explains better.

Frank -- Oh my bad -- iternet translations...

Seth- At the top of this page ..I did before I wrote the article above ):h

I think everyone should do the figures them selves...even if you use the DIC it should still say if you are losing or gaining MPG....I would think a huge fiberglass tonnue weighing in at 150 or whatever would have an adverse affect on mpg?

Someone should Put up a poll have everyone do a tankfull: tailgate up and a tank full down then chime in on the pole: better, worse or same...no numbers to mix up that way...
Guess we would need two polls one No Tonnue and one With Tonnue-
People with could drive with Tonnue on and Tonnue off w/ tailgate down!

Realworld no BS!

"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."

Hmm... If a tailgate improves mileage 10%, how about if I put a parachute on the back? 50% better mileage? Nevermind, it drags on the ground when I stop.

How would you personally test? Find a steep long hill. Find what your top speed is going up. Remove tailgate. Try again.

After looking carefully at their data...

They may be right, or they may be wrong. Very sloppy.

A Corvette has a Cd of about .31, anyone believe a pickup is more aero?

While they said they tested at various speeds (22-155mph???), the data comparing various speeds is missing.

And how about their professional test equipment?

http://sitemaker.umich.edu/um.gm.truck/files/cabex70_4_cropped.jpg

Someone either was in a hellava rush, or smoked one too many bowls when setting up the test.

They COULD be right. But that data doesn't mean much.

The NASCAR truck guys run fully enclosed beds. You don't suppose they know something about aero? Later! Frank

As part of my campaign to win biggest nerd on the site, I offer the following:

On my old gasser, I had both an installed computer (now in the new truck) and a Pace Edwards remote controlled rolling bedcover. The PC was running EFILive software that let me read engine data in realtime and I programmed it to calculate instantaneous mileage based on fuel flowrate and vehicle speed.

On the long flat (and boring) stretches of highway 290 between Houston and Austin, I would set the cruise at 70 and open and close the cover. Mileage was always 0.5 to 1 MPG better with the cover closed.

Same engine, same temperture, same winds, flat road, same tires, everything.

Oh, and BTW, windows vs. A/C made no detectable difference.

GUYS, the study only cited drag coefficients, not MPG's. Also, when doing comparisons, you have to drive the same stretch of road w/ same fuel load, and atmospheric conditions, etc. It is not a true comparison for instance on a 500 mile test to drive the first 250 miles tailgate up, then the next 250 miles tailgate down. Too many variables, temperatute, atmospheric pressure, and altitude to name a few. Sorry, my little rant.:rant:

At one time I had a POS PU truck that when i droped the tail gate I could more easily do the speed limit or even break it on occasion!!!(65MPH), with the tail gate up I struggled to do it unless I had a tail wind. So many stories about that truck.......

Regardless of all that -- I bought a retrax :)

Just made a quick trip to West Nebraska and while on the road thought about a few things with this study. In a controlled invironment with the test pickup, I don't doubt their results. However what about long beds, crew cabs, cross winds, head winds, etc, etc. Nothing in the test to say how much rear tire loading increased with the "bubble" of air being forced down in the box by the air flow over the cab. Less drag maybe but maybe more tire loading and less milage. Like somebody said eariler drag does not directly translate to mpg. My tests have appeared to favor removal of tailgate. Makes me feel better may not work for you.

If you drive with your tail gate down how to you keep stuff from coming out the back?
And if you don't have any thing in the back then why are you driving a truck? If you are worried about a few cents in fuel, you can drive a car and save dollars instead of cents

Load your truck with a forklift driven by a guy in a hurry who doesn't speak English too well, and get back with me. 90% of the time, I DON'T run a tailgate and it has nothing to do with mileage. And yes, I too lazy/old to put on and take off the tailgate a few times a day to avoid getting it folded in 1/2.

Hmm... If a tailgate improves mileage 10%, how about if I put a parachute on the back? 50% better mileage? Nevermind, it drags on the ground when I stop.

How would you personally test? Find a steep long hill. Find what your top speed is going up. Remove tailgate. Try again.

:funnypost :badidea: People will drive over it all the time. :lol:

Load your truck with a forklift driven by a guy in a hurry who doesn't speak English too well, and get back with me. 90% of the time, I DON'T run a tailgate and it has nothing to do with mileage. And yes, I too lazy/old to put on and take off the tailgate a few times a day to avoid getting it folded in 1/2.
I don't use the tailgate either. With all the goings on, different trailers, drivers, etc, it is more in the way than not. Just this last saturday I picked up 20 bags of cement mix at Home Depot and had them load the pallet onto the truck with one of their forklifts. Even without the tailgate the guy (who spoke English well) managed to push the truck with the lift.

On the previous truck I had a board that I wedged across the back of the bed when I needed to keep stuff from sliding out. I am planning on buying one of those tailgate nets for the Dmax that I can store behind the seat when I don't need it.