In January 2007, SEMA’s Market Research Department conducted a study to test the affect tonneau covers have on the coefficient of drag for pickups. Four trucks were tested: a 2006 Ford F-150 with a 5' 5" bed; a 2005 Ford F-150 with a 6' 5" bed; a 2006 Dodge Ram 1500 with a 6' 5" bed; and a 2007 GMC Sierra with a 6' 5" bed. These trucks were tested at the A2 Wind Tunnel in Mooresville, North Carolina, with 13 different tonneaus from nine different manufacturers.

Rising gas prices are not only a concern for consumers, but also for truck manufacturers and anyone who manufactures aftermarket parts for pickups. If consumers decide not to buy pickups because of their gas-mileage ratings, a lot in the industry suffer. If consumers see that the addition of a tonneau cover could improve fuel economy, they may continue to buy pickup trucks at the rate they always have. After all, a truck enthusiast would much rather drive a pickup than downsize to a subcompact.

The wind tunnel test produced great results. All 13 products tested improved the coefficient of drag, Cd, by at least 4.2%. The improvements ranged anywhere from 4.2%–7.8%. Other tests would need to be conducted in order for fuel economy to be calculated, but it is safe to say that a reduction in drag would improve fuel efficiency for these pickups.

Six products were tested on the 2005 F-150. Cd was normalized to 1 for all pickup trucks. This was done in the interest of both the truck manufacturers and the tonneau cover manufacturers. This also makes it easier to report percentage decreases in Cd. The following chart shows the results. You will notice the baseline Cd value for the truck is represented by the blue dot at 1. (Baseline values were calculated for the trucks at a wind speed of 85 mph, with no tonneau installed, tailgate in upright position) You will also see the values for the test with the tailgate down. As you will notice, lowering the tailgate has little effect on Cd.

i believe i watched an episode of MYTHBUSTERS. the show in the discovery channel. and they did a scientific study on the gas savings when driving a truck with tailgate up VS tailgate down. and they savings if i remember correctly were slim to nill. basically amounting to a few dollars for the year. i believe controling your gas pedal has the biggest effect. slow down, save gas....but have less fun doing it. haha

__________________
2006 Titan 4X4, 24" U2-55 wheels, custom PRG 3"/5" drop, Gibson Dual sport exhaust, K&N intake, DunderDan 4 pc silver painted grill, factory fogs, fog jumper(on with marker lights), LED tails, LED third brake light, chrome Tailgate bezel, Armada spolier, LINE-X bedliner, chrome front blinker bulbs, Access tonneu, big tow mirrors swapped for regular mirrors, chrome mirror covers, SS window sills, tinted front windows 20%

http://www.myspace.com/sixt7ninr

Using the above wind tunnel results we now have the following facts.

• Drag is reduced w/ a bed cover
• Drag causes increased fuel consumption

Therefore, MPG should improve. The next step is to redo the study w/ each truck with and without a bed cover. Simple, Fast, Concrete results (if done right). How much improvement in MPG results from a drop in drag of 4-8%? I hope they did that next step. Please post those results if they did.

I'm getting a cover soon. I can do a study of 1 truck, but if the difference is small, it will be hard to provide significant proof to apply to all Titans. We will just have a strong hint. Myth busters did do a small study that showed a tail gate UP had better MPG than down. The hypothesized (guessed) that a tail gate up ride cause a "vortex of air" to circulate in the bed and thereby reduce drag. They never tested that guess, and I think a cover would do that much better anyway. The next step is for Mythbusters to get Bakflip to sponsor an episode to do the study w/ and w/o.

Dunno...
but Annotated Mythbusters: Episode 64: More Myths Revisited

I've seen the shows they did on it... and I still have a cover...

__________________
05 KC SE Smoke
01 Suzuki 600 GSF
88 Fiero 2M4

Question: If a tonneau cover helps mileage, do the bed caps help as well? They modify the air flow over the truck as well...

They probably should, but any gains would likely be offset by the extra weight.

__________________
05 KC SE Smoke
01 Suzuki 600 GSF
88 Fiero 2M4

Every pick-up I've ever owned, I have installed a tonneau cover. At highway speeds you can feel the difference. The one on my Titan is the Trifecta from Extang. This is the best one I've ever used.
Hard covers are great but, I have no place to store one when I need a open bed. The soft tops resolve this.