Very clearly in this video he says "Tonneau covers are more efficient." (transcription given above)


There are 16 responses to this thread that say definitively 0% nada nothing, based on research, yada, yada, etc. People believe what they want, despite conclusive evidence to the contrary. This is our truck, not some other brand/year or other distinction. Not Mythbusters, not the Tonneau Cover Manufacturing Society. This is from Ford with wind tunnel evidence, not subjective anecdotal drivel from individuals. Yet several people want to spread the inaccuracy of their belief of 0%. The Reticular activating System at its finest.

 

Of course it does, at lower speeds when the air pressure in the bed doesn't form enough bubble, the cover works better. It will also reduce the drag created by the air hitting the tailgate, But, the difference between having one and not having one are only measurable over long periods of time. IOW having one wont magically gain you 2 more MPG. The Mythbusters was in regards to not having a tailgate, which the videos also clearly state the same.

 

Well I would expect the topper to be worse, since it's like the back of a brick. That's a lot of surface area for a low pressure zone sucking on the back of the vehicle.

 

1.35mpg at the most, at 85mph. Extrapolating to 80mph would be more like 1 or 1.1, so more like 16mpg instead of 15mpg.

 

Remember that in a wind tunnel there is no side wind, it's only from the front and not at 60 MPH. Even a 30 degree difference in direction from travel will cut over and fill a portion of the box with momentum reducing wind and eddies. Higher speed causes more turbulent effects as well.

That said, a cover isn't going to pay for itself if that's only what you are looking for.

 

Maybe mine helped the fuel economy but I can confidently say I noticed 0 difference. Or at least small enough change for me to not notice.

 

I wouldn't expect any increase with the cover I have as it weights about 80 lbs and that off sets any benefit from it.

 

mine did not change at all with a cover. Its all controlled by the right foot

 

According to a 1982 Popular Mechanics article/test A tonneau increased MPG by 9% and a topper increased mileage by 13%. I don't know how reputable the test was but they did try.


I suppose the specific topper you use could drastically affect how well it works. Some, as you say, are indeed square like a brick and others have a bit of slope that leads to the tailgate "fin". My topper has a slope of about 75° compared to the truck back window slope of 90°. I haven't seen any topper manufacturers tout wind tunnel tests. SnugTop was involved in the previously mentioned SEMA testing and seemed to conclude a top speed of slightly less with a cab high topper. They attributed the reduction to the weight.

 

Very interesting, thanks for sharing!