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[xboxbox451]

Some of you are probably familiar with this, but its the first I've seen it pretty much disproved.

I never owned a pickup, though I always wondered if by driving with the tailgate down does that actually improve fuel efficiency by reducing drag. I recently saw a Myth-Busters episode that tested this very theory, which had some interesting results. Not sure if this episode is old or new.

As the Myth-Busters pointed out, by keeping the tailgate UP, a phenomenon known as a "Locked Vortex Flow" is created, which essentially is a fast moving circular bubble of air that builds within the bed. This bubble of air then prevents the rushing air over the cab from pushing down on the tailgate.

By keeping the tailgate down the air rushing over the cab then gets caught in the bed pushing down on the open tailgate and creates drag. So leaving a tailgate open actually reduces fuel efficiency by creating drag.

The one thing the Myth-Busters didnt test was using a Tailgate net. According to their tests, drag was created by air flow pusing down on the open tailgate. Since the tailgate is removed upon adding a net, I wonder if the same drag is created?

I recorded the Myth-Busters segment showing their experiments. Very interesting.

Video link on YouTube. 7 Mins, .Wmv format, 10MB stream

[lostboyz]

i really dont think mythbusters can always be trusted, I put mine down and seemed to get 3-5mpg better milage on two 800mile trips, though I suppose it couldve been the way I was driving but Im really torn on believing them here.

[twistedsymphony]

I saw that episode just recently too, kind of interesting stuff...

I would imagine that the net would have the same effect as leaving the gate down but not as dramatic.

I think that the best efficency comes if you have a cap or bed cover though...

[thewickedjester]

QUOTE

I would imagine that the net would have the same effect as leaving the gate down but not as dramatic.

I would think it would have roughly the same effect, if you think about it, the reason you get this supposed 'locked vortex' is because the tailgate forces the air to go 'back up' and create the vortex. They are saying that leaving the tailgate down forces air to hit the open and exposed area of the bed, not specifically the tailgate, although I'm sure the tailgate down doesnt help...

What I want to know, whats it like using a deck lid? After I get some of the other body work on my truck done I'm working on lining up a wet sanding, a bed rug kit, and a deck lid. I wonder how that'll affect it...

[ClintiePoo]

QUOTE(twistedsymphony @ Jun 5 2006, 02:38 PM)

I would imagine that the net would have the same effect as leaving the gate down but not as dramatic.

I think the net would be worse, because it would cause more turbulence in the air going over the truck.  More turbulence = more drag.

[Owtlaw333]

This was all disproved long before the Mythbusters did it. I was just happy to see them do it cuz it has a larger audience. But the first place I saw this was in an article in Motortrend a couple years back. Most trucks (as with all vehicles) are designed with aerodynamics in mind. Trucks are meant to be driven with the gate up. I believe the verdict in Motortrend was that it's worse to have the gate down than up, but it's worse to have one of those cage things than it is to have nothing at all (which I found interesting).

So you can not believe the Mythbusters if you'd like... but when it's coming from two sources, I would think it's true.

[lordvader129]

QUOTE(lostboyz @ Jun 5 2006, 12:10 PM)

i really dont think mythbusters can always be trusted, I put mine down and seemed to get 3-5mpg better milage on two 800mile trips, though I suppose it couldve been the way I was driving but Im really torn on believing them here.

well if your going on a long trip i assume it was highway? less stop-and-go driving always improves mileage

QUOTE

I think that the best efficency comes if you have a cap or bed cover though...

thats somethign ive wondered, ive sent several emails to the mythbusters asking them to re-visit this one and test tonneau covers, to me it seems like they would have the same effect as tailgate down

[thewickedjester]

QUOTE

thats somethign ive wondered, ive sent several emails to the mythbusters asking them to re-visit this one and test tonneau covers, to me it seems like they would have the same effect as tailgate down

Yeah, its bassically just moving the 'point of impact' on the truck vertically higher. Though you may want that if you are putting on a lot of highway miles (as I am known to do for work) when you go to pass the extra traction might help... I've been in trucks/cars/etc where you go into passing gear and just floor it and the rear wheels break loose just a bit. Oh well, I doubt it makes any difference, I'm still gonna get a BedRug kit and decklid for my truck hehe.

[xboxbox451]

QUOTE(lordvader129 @ Jun 5 2006, 06:34 PM)

ive sent several emails to the mythbusters asking them to re-visit this one and test tonneau covers, to me it seems like they would have the same effect as tailgate down

I was checking out how retailers market these covers. Of coure they claim a cover reduces wind drag. But do they realize that there's really no drag to begin with?

Sounds like false advertising, or at the very least ignorant advertising.

QUOTE(Car Stuff.Com Ad)

Decent fuel savings. With gas prices surging, one way you can save as much as 10-15% at the pump is to have a tonneau cover installed. Wind drag is greatly reduced when your tonneau cover is securely in place.

SOURCE

Of course their trying to capitalize on the rise of fuel costs with such rhetoric.

If a locked vortex improves the aerodynamicy of a pick up, then the void created by the bed is very much needed. Of course that void wont be there when your hauling, but when your hauling concern for fuel efficiency pretty much becomes a dead issue.

As thewickedjester pointed out the point of impact is greatly reduced with a cover, so drag may not be as great with the tailgate down.

[lostboyz]

I wasnt comparing it to normal driving, but I had a there and back thing, one with it down and one with it up. But me driving speed and all that swings with the day so i probably wasnt being the most scientific with it

[lordvader129]

QUOTE

As thewickedjester pointed out the point of impact is greatly reduced with a cover, so drag may not be as great with the tailgate down.

yeah, i figured since it was a smooth surface it wouldnt be as bad as tailgate down, butgiven the vortex the mythbusters showed, i dont see how it can be as good as tailgate up

[Rylinkus]

My truck seems to get better gas mileage with the tail gate removed. And most certainly gets better Highway gas mileage with a toneau cover vs tailgate up. I think what happens in a lot of these tests is that one or 2 vehicles are used to explore what happens with every truck. And that simply doesn't make sense, because all though the overall shapes are roughly the same, the minute details that create the air flow over the vehicle may differ dramatically one vehicle to the next.

[ClintiePoo]

Until I see a conclusive CFD study, I won't believe one option is better than another.

[thewickedjester]

QUOTE(ClintiePoo @ Jun 6 2006, 11:36 PM)

Until I see a conclusive CFD study, I won't believe one option is better than another.

At the end of the day, I think we have to remember, what was the difference in gas consumed? I dont think it was into the 10gal+ range when they were done... so does it REALLY matter? If you have to manage gas that much that the difference is killing you then you really shouldnt be driving a truck

[garver]

I have a cover on the bed of my 98 chevy 350 used to pull my camaro to the strip. when just driving around to places i get aboujt a 2-3 mpg increase on this beast i went from 8-12 mpg to 11-16mpg