I thought they recorded empirical data with the tailgate removed... I'm fairly certain that factored in the weight reduction...

And even more especially at steady state -- not accelerating (unless the mass removed from the vehicle was spinning).

soft toneau cover might be the answer , i installed one on a 07 frontier that had to weigh around 20lbs. but I cant stand those big zippers on it,pulling/tugging to get the end zipped up is a pain.

lol or the evil snap kind! even worse...

Does anyone have any figures with respect to truck caps? I know when I removed mine I didn't get kicked around nearly as much but unfortunately I wasn't keeping track of my FE numbers at the time... :$

On the bright side, I do know that with the cap off and the tailgate up I destroy my EPA numbers, old or new...

Matt

I just added a truck cap to my truck. I checked mpg just before and got 17.8 and then right after and got the exact same. My cap is taller than the height of the truck by about 3-5 inches. It is slanted up at about the same rake as the windshield. I was wondering if the non cab high height would effect mpg negatively but it seems like it hasn't.

It probably has reduced FE compared to a cover that didn't increase the frontal area of the car....

That was my experience as well, my '86 D-250 did get an improvement with the tailgate removed (std cab) but my '95 club cab did not.

Best I can recommend is do your own experiment, mythbusters is entertainment.

As for it up or down, I never understood this concept.
If up is the answer there is nothing more doing, have a nice day.
But if down is the answer then take it off and install an air mesh gate, saves another 20+ pounds of weight, why leave the stupid thing on?

Bah, what a useless study. Why is it the only short beds they had were extended cab and the only long bed was a standard cab?

Does length of cab make a difference?

They studied full toneau or not, but why didn't they try with cap or not, that interests me greatly.

Also why do they continously admonish putting the tailgate down when the 8ft bed showed positive results at anything over 0 degree yaw (and not that bad of a negative effect at 0 yaw either).

I guess I should do my own experiments but without a scan gauge and at my low MPG the variance is so high I doubt there's any real way to tell what helped and didn't.

Mythbusters also tackled this issue. Basically, there is a bubble of air that is trapped in the bed causing the airstream to go over it as if there was something there. So tailgate up is best.

Last year when I was on a working trip to South Africa, I ended up on a race track outside Johannesburg where the local motor club arranged a speed trial open to anyone. They used a radar to measure top speed after the rather long start/finnish stretch. The cars were doing flying starts so most of them seemed to reach "terminal velocity". One of the fastest cars was a very turbo charged Japanese pickup. After a couple of runs, I suggested they should tuck the mirrors in and remove the tailgate to increase top speed. To my surprise, they got significantly lower top speed with that setup (sorry, don't remember the figures). They did try several times but it just didn't work. I never got an explanation to that until I started to read these forums...