I was a engineering student at tech when they did this study in there wind tunnel and the truck with the tail gate up got 2% better than the one with it down.

 

I think it was RUSLOW that once said something about having a bed cover and no tail gate could make the rear unstable at high speeds

My best times down the strip are with a soft cover, tail gate on & up.

 

Truck looks SICK

 

When you drive with no bed cover and the gate UP, you create a stagnent pocket of air in the bed. This air pocket acts like a cover, and deflects most of the new incoming air coming over the cab. That's why if you have leaves or debris in the bed and you drive around, it usually just swirls around in the bed instead of immediately flying out. This action makes the air going over the truck smoother and allows it to gently pass over the bed, creating less drag.

When you put the gate DOWN, the air coming over the cab now slams down into the bed, creating a vaccum, and puts more drag on the vehicle. That's why you get better gas mileage with it UP.

Of course, having a bed cover is the most optimum way to have it.

 

sent this link to a buddy with a tocamo pickup that swears that he gets better mileage with the tailgate down.
he did some research and found this

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

 

Another important factor in reducing drag is lowering. If you punch a smaller hole in the air, drag comes down.

On a pickup;

1-Is there a big difference in reducing turbulence under the vehicle with the use of panels, like the cars do. Take a look at Lexus or BMW

2-What is the best type of wing design to use to increase down force?

TB

 

Just notice where the "lift" on the tonneau cover is, and where there is "pressure" on the cover.
It appears to me that the air is flowing over the cab to the middle of the bed, then slaming down on the cover......
I wonder if with the tailgate missing, the air gets sucked into the bed, causing a vacumn, or thats just air pushing down
Don't know how that relates to gas milage/ drag, but some interesting pics non the less..............

 

I'm with Stan here ... Having run with and without the soft tonneau
on-track, with the stabilizers in and out, I found the best combo and
the most "downforce" with teh cover on and the stabilizers removed.

Of course this is just seat of the pants comparison.

 

quote from: Ed Fitzgerald, Research Assistant, Dept. of Aero/Mechanical Engineering, U. of Notre Dame

"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."

 

Gator........sure would like to see that truck at rest.That will also tell a story.I know that before I made the splitter for my truck the front would raise up atleast 2 inchs at speed and by the looks of that one it is worse.Stan

 

I notice that my truck's tonnue cover(extang low profile snapless) with the tail gate on and up, on the road at all speeds above 30 mph, does the same thing as the pictures in fast gators post.

 

Cliff,
what do you mean by "stabilizers"?

Den

 

Stan

That's Mike da Cops truck and he doesn't have a photo gallery that I can find. I found this pic, but Iam not sure if it's his truck, with the billet gas door. Can't really tell...........

**edit**
nevermind that wasn't his truck
I'll see if I can get a pic of his truck and will post back here

 

I have a soft cover on my tow rig, and it has that bubble even with the tailgate on when I am on the highway.

 

I did this type to testing back when I was in college in the late 70's but in a wind tunnel not a water tunnel (tank). It's been done almost every year by aerospace students accross the country. The water tunnel results have always been off. The wind tunnel always shows little to no effect with the tailgate up or down. The air passes over the cab and over the tailgate. That is at speeds up to 100 mph. I haven't seen the test above that.