I just wanted to let those of you who did not know (because I sure was surprised when I found out) that you will get SEVERELY WORSE MPG is you leave your tailgate down than if you leave it up (with or without a tonneau cover). This is caused by the circular airflow created behind the cab that creates an air disturbance that greatly reduces fuel economy.

Just wanted to let people know in case they were incorrectly trying to pick up some MPG by leaving the gate down!!

More MPG for all!

 

I've done some serious research on this subject and found the above to be true.... Lots of drag coefficients and squirling thingys with the air in the bed....







Thanks Myth Busters!! Lol

 

O yea, I wanna add a part here. To those who expect 20+ MPG. Please remember that you did purchase a 4 TON HUNK OF STEEL!!! I'm very happy with our MPG Cuz I'm aware that we bought a 4 ton hunk of metal thats aerodynamically challanged...

 

Tis true, I believe Mythbusters did a bit on it as well. With the tailgate up there is a rotating mass of air in the bed that the air over the cab rides over (imagine a tarp stretched from the cab to the tailgate, same principle). You can deffinetly see it if you leave trash in your bed and cruise down the interstate, it doesn't blow out, it will just circle.

Apparently there are a lot of people that don't watch Mythbusters as I see downed tailgates all the time...

 

So you guys are sayin less with a tonneau as well. That sux!
I just ordered one

 

I'm not sure about that, I can't remember if Mythbusters covered that scenario or not...

 

I saw the show and still do not believe it. Seems like every truck I have had gets better mileage with tailgate down. I even did a long term test with my last truck. I drive interstate 33 miles each way for my job. I drove two weeks with tail gate up and then two weeks with tail gate down. I did this in the summer time here because we can have several weeks of VERY similar weather. I got better mileage with tail gate down.

I have kept a very detailed record of mileage with my current truck and it shows an increase in mileage when I installed the tonneau cover. FWIW I still say tail gate down is better.

 

No it has nothing to do with tonneau covers. They block the air from entering the bed. The bed sides cause the air spin and turbulance with the tailgate down. This can not happen with a cover on

 

No matter how you do it, I can't see the difference being more than 1 MPG. I do subscribe to the tailgate up method though. If you think about it, when you put the gate down, the wind travels through the bed, and hits all those little projections (wheelwells, and the little square thingys that you put the stakes in). If you don't think they catch much air, stick your hand out the window at 75, palm facing the front, and see if it doesn't catch a little wind.

 

My mileage is the same, with or without tonneau cover. I never run with tailgate open because I don't want the fenders to flex out and become loose. But I never noticed any change in mileagw/tonneau.

 

I think Sport truck magazine (I know, not the Diesel bible) had an article on how milaege was better with the gate up. They also added that the tailgate give support to the bed sides which extends bed life.
(hope I got that right).

 

I was wrong, it was in Truck Trend Magazine.

http://www.trucktrend.com/features/c...odynamics.html

 

Yes, Myth Busters is where I got the info from as well. One DTR member was saying that his father noticed routinely 1/10th of a second SLOWER 1/4 mile times with the tail gate down. That means that there is enough air disturbance to add 100lbs. worth of drag (100lbs. is about 1/10th in the 1/4 Mile).

 

What about flat beds?

 

tailgate up is fine with me, i got 25 mpg on the way home the other day, ofcourse i was doing 60 the whole way just to see what it would do....this speed limit thing might actually help my mileage....but id rather get 18 and go fast! lol