wind drag

Why does everyone have to use KM? Are you canadian?

The world is bigger then the US.

Are you talking about a flat bed cover or a canopy-type shell?

Sellers of flat bed covers, canopy-type shells and mesh tailgates claim that you will get vastly-increased gas mileage when you use their products. The flat bed covers and canopy-type shells might reduce wind drag, but because they add weight to the truck, their positive effects are somewhat reduced.

However, there are engineers who use wind tunnel tests to demonstrate that putting the tailgate down actually INCREASES wind drag, particularly on a short bed truck. Even though this information has been common knowledge for over 20 years, you still see people driving around (and parking) with their tailgates down. This practice lowers the structural integrity of the truck, increases the chance of major damage from a rear end collision and endangers the safety of pedestrians who could be injured by walking into the tailgate.

A mesh tailgate adds insult to injury because it costs money, looks bad, lowers the structural integrity of the truck and increases wind drag. Some who don't want to run the risk of driving around with the tailgate down take the tailgate off and put it in the cargo box -- just in case they might actually need it for hauling cargo. One test shows that removing the tailgate causes more wind drag than just leaving it in the down position.

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TAILGATE UP OR DOWN? If you're interested in maximum fuel economy from your pickup truck, and the bed is empty, should you run it with the tailgate down? Most people would probably answer yes, figuring there's less wind resistance that way. Well, there are researchers who wonder about this, too. And one of them used a wind tunnel and data on wind currents in North America to come up with a scientific answer. His name is Kevin Cooper of the National Research Council of Canada, and he reported his findings at the Congress. His results are:

Except for trucks with a full 8-ft. bed, the Cd (coefficient of drag) is lower with the tailgate up.

With the tailgate completely removed, the Cd under most conditions is higher, even on trucks with an 8-ft. bed.

Using wire mesh in place of a solid tailgate also increases the drag.

Using a cover over the bed reduces drag, but a partial cover (half the length of the bed) is somewhat better than a full cover. Actually, this confirms research done by General Motors, which patented the idea of a partial cover back in 1986 (the patent has since expired).

For what it's worth, the bottom line according to Cooper: You don't save a lot of gas, but if you want to drive a pickup and be environmentally conscious you can make a small contribution to the common good. On a pickup with an extended cab and a 6.5-ft. bed, you'd save 60 gals. of fuel over 100,000 miles if you leave the tailgate up instead of down, and 172 gals. if you leave it up instead of removing it. On a standard cab with an 8-ft. bed, you'd save as much as 207 gals. if you keep the tailgate up and use a bed cover, vs. the tailgate down with no cover.

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In the 1970s aircraft production went into a slump, and Lockheed started looking.for other customers for its wind-tunnel services.

Prime candidates were automakers, and Lockheed was successful in convincing Ford, among others, that the wind tunnel wouId help them reduce drag and wind noise on their vehicles.

Needless to say, in the past 15 to 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 nonaerodynamc 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 Department of Aero/Mechanical Engineering University of Notre Dame

Not being a smartass, I just see a lot of people using metric, and I wondered. Sorry if I offended you in anyway.

obviously someone has a problem with KM.

for you less educated it works out to be 160 miles

...' than '...

I noticed a 2MPG difference on my 1988 Chevy S10 when I removed mine, as well as improved performance. I attributed it to sheer loss of weight. A tonneau(SP!) cover removal could probably cause that. I think the other poster's study says that they do alright. A straight line from the cab to the tail gate end is best. However, how many tanks have you calculated off of? 3 would be about the minimum. There are also allot of things that can eat at fuel mileage, any kind of performance symptoms? Forget to take the dead bodies out of the back?

GMC Gremlin

Hello Michael,

1 mile = 1.609 kilometers 1 km = .6215 mi

600 km = 372.90 mi

500 km = 310.75 mi 100 km = 62.15 mi

What works out to be 160 miles?

Just curious...

Franko

2004 Canyon reg cab 4 cyl

Tonneau cover improved average by maybe 0.5 l / 100 km.

Best mileage I ever got was highway, 1/2 tank on cruise @ 120 km / hr, and

1/2 tank on the pedal between 130 - 140 km / hr. My average is 11.3 l / 100 km, that trip (450 km total) I got 9.1 l / 100 km!!!

Como? Four tanks in a day?

GMC Gremlin

guess I kinda worded that wrong. :)

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Removing the tail gate removes structural rigidity from the truck and nets you worse horse power.

GMC Gremlin