I agree with you.

 

My '97 f150 saw a 1-2 mpg improvement after installing a cover, mostly with highway driving. No diff. either way with city driving. The barrier between theives and my stuff was a big plus too. Too bad it didn't stop em from stealing the whole truck, but that's another story for another thread.The best thing about the tonneau was how much better the truck felt at highway speeds. The low-pressure bubble that forms in the bed without a cover gets disrupted by other big vehicles or cross-winds which create lateral forces on the truck. The tonneau really made a difference in my opinion. I'm saving up for a cover for my '04 replacement and can't wait for the improved ride on my cross-country trips.

 

re Tonneau:
Think smooth. The interior of the bed has lots of surfaces that the air can drag along at any speed. The open box with tailgate up vs down actually supports the use of the tonneau. The tailgate in the up position traps a mass of air behind the cab. At highway speeds air passing over the cab, can't tumble into the bed because this trapped air is there. The result is better airflow past the truck and better fuel economy. With a tonneau in place the majority of the ball is there at ALL speeds and without turbulence. But the better shape is a cab height cap. For me it's a no-go. I don't like the reduction in visibility and I want flexibility in what I can put in the truck whenever I want to. Remember that the Shelby Cobra GT was a Kammback shape and faster than the roadster despite the added weight of its structure.

In the 80s we tried a lot of low tech things to improve our personal vehicles. Including skinning the underside of the truck then doing coast downs from the top of hills. Smoothing things out helped, but you had to be careful about dissipating heat from under the hood and along the exhaust system.
One interesting thing was the addition of a vehicle wide strip of flower bed edging attached below the radiator as an air dam. The extra 3 inches of frontal area at the point was offset by the fact that the air passing it avoided contact with the underside of the engine. It was nearly as effective as skinning.

 

If you did a search for THE MYTH BUSTERS tv show...they did a segment on fuel milage with two F150s one with the tailgate up and the other with the tailgate down. They drained both tanks so the were dry and added gas in equal ammounts. I don't remember how much. They drove them at a specific mph till they both ran out of gas. The truck with the tailgate up went father than the one down by 5 or so miles.

 

I've seen that. And after thinking about it. If they used 2 different F150s, how do they know they both got the same mileage? What if 1 had a tune up, the other didn't?

PS. I don't remember how many gallons they put in the truck. So if it was only like 1 gallon, even a 5mpg gain is ALOT, so obviously it does help.

 

I have a 2005 FX4 Step Side. Retrax cover,5.6 engine,dual exhaust,K&M Cold Air. I bought this truck new in 2006,enlarged the tires one size. I have checked the milage tank to tank,and I get 17 mpg.I drive hiway speed 70 mph. When I installed the cold air and duals it upped the mpg by 2 miles.

 

They don't make a 5.6.. 5.4 yes.

 

I think they used two new trucks

 

hell i thought they used a dodge dakota????..the same truck...the whole time..even tried a hard covor...tail gate up ..and down...and off...and a cargo net....or did i dream this...lol

 

Exactly. The tailgate being up already creates the low pressure zone. If the air isn't moving putting a cover on the bed won't change that.