Actually Myth Buster tested this, 2 trucks, identical, both programmed to drive the same speed, same amount of gase, etc. and the results were that with the tailgate up, the wind coming down off the back of the cab would flow down and hit the tailgate, and flow back to the cab. This effect created a circular motion of air between the back of the cab and the tailgate, which "accelerated" the air coming off the back of the cab down over the tailgate, createing an aerodynamic-like flow, while with the tailgate down caused the air to just flow over the cab and with no tailgate to create that accelerated circular motion, it just kept flowing down alog the bed and wrapped around the tailgate, which caused a drag on the vehicle. It sounds very very weird i know, and i didnt explain it too well, but in the end the truck with its tailgate up went miles past the one with the tailgate down.

Note: the test trucks were FORDS ick, so that could be why this seems so F***'d up haha[8D]

 

I'm going to have to find that episode now.

 

to be honest with you i was shocked...but after they showed how it works it all made sense!!!

 

They can say it all they want, but I know people who get better mileage with the tailgate down.

 

Not to get off topic Daddywags but you might want to check out this post.

https://dodgeforum.com/announcement.asp?id=13

 

I heard about the myth buster show... their testing method is crap. one one of their shows they tested 2 identical trucks with the exception of the tailgate up vs down, there is no way to compare up vs down with 2 trucks, it has to be the same truck in a controled environment.

the better way to test it would be to put the test truck in a wind tunnel on a dyno, load it down and simulate 65~70 mph driving over a long distance and do it with both tailgate up and down. those test results would be more meaning full when compared to 2 different trucks on the same route.

Go look at the MPG polls on every forum and see how much 1 truck varies from another... they're all over the place.

 

"Daddywags" Since I am a Steeler fan I resized it and touched up your sig for you....

[IMG]local://upfiles/30292/BC65E20998CC4A4F9C1CEEA943A6CD80.jpg[/IMG]

 

that's true steve.....i'll agree with you there,

but myth busters aside, can anyone honestly say that having a tonnue cover or an open bed with their tailgate down has made a noticable difference in their gas mileage. I cannot. Trucks arent supposed to get good gas mileage anyways, you want gas mileage, go buy a geo metro-type econo cruiser.

 

Nobody buys a truck expecting phenomenal gas mileage, true... However, when some people are getting 10MPG, and others are getting 20MPG... I am sure that the people only getting 10 would like to know how others are acheiving 20MPG...

However, I don't think that people claiming 1MPG improvement from a tonneau cover is relevant. Say you spend $1000 on a really nice fiberglass cover with the gas shocks and stuff to automatically raise it... Whatever... Then say you drive a lot, like 20,000 miles in a year... Say you get 21MPG with the cover, and only 20 without it... That extra 1MPG will only save you $200 in the year. Assumig gasoline was Approximately $4/gallon, you would fill up with 1000 gallons in a year, at 20MPG. You would fill up with 950 gallons, at 21MPG...

You would have to drive that truck for 5 years, to recoupe the cost of the cover.

 

Exactly the reason I got my extang. Rolls up and I did have a 1mpg increace in mileage. I caculated at fill up and not trust the truck computer. I average 16 to 17 mpg to and from work with about 80% highway. Pretty good for only paying 200 from truckxpressions.