Finally the myth is busted.

On Mythbusters tonite they did a couple of interesting tests.
One we might be interested in was the Tailgate UP/DOWN for Fuel economy.
First they loaded up to Identical trucks and headed off for California.
The one with the Tailgate DOWN ran out of gas first!

Then they put a model truck in a tank of fluid and used some dye to watch the flow over the cab and out the bed.
Lot's of turbulence in both cases.
So they put some Oats in the fluid and watched as the Oats circulated.

The Roll of air, or Cushion built up in the bed, just behind the cab with the Tail gate up. This let the air flow smoothly over the cab, the cushion of air and out the back.

Next with the tailgate down, the Oats rolled around and around behind the cab, and the air flow went over the cab and down over the oats and out the bed over the Tailgate.
That created a 'low pressure' or Drag just over the tailgate. Increasing the load on the Engine of the truck.

 

yea but there are also a lot of other factors that that contribute
like driving, one person could drive faster and put his foot off and on the break more often than the other as well as giving it more gas than needed in certain areas
pumping the gas...
were they the exact same model trucks?

there are a lot and lot of factors that contribute

 

Yup, the exact same trucks. Same route, same rules for both drivers.

The proof as to why that happens is in the Oats flowing around the Model truck in the Tank.
It shows that the faster you drive with the tailgate down, the worse the drag gets.

With the Tailgate up, the bubble behind the cab stayed the same shape and kept the air (pilots call it Laminer air flow) flowing over the complete truck.

How a person drives would only affect his milage, as opposed to somebody else's milage.
But no matter how anybody drives, you'll save gas by keeping the tailgate up. They prooved it.

 

Consumer Reports did a test on this subject about 10 or 15 years ago. They found that with the exception of a Toyota truck, the mileage of all pickups went down when the tailgate was left down.

 

ive heard of this test before the mythbusters done it, and it had the same results....but, the test was done on new model trucks which have better aerodynamics than a brick in the wind like my 76 F-150....what i want to know is if anyone has done this test on a 73-79 F-Series.....

 

There was another thread on this exact subject recently. Do a search. All the claims and angles have been examined. Bottom line, tailgate up is best.

Also one member on that thread made a canopy and was testing to see how much improvement he got.

 

I love the mythbusters but they do neglect a lot of things and i try not to take their results too seriously but i felt that they did a really good job with this one and the model they made really helped me understand why the tailgate up helps. And yes even on a 70s ford truck it would still apply because you still have that air bubble in bed, I've noticed it in my 79, if you have any paper or plastic bag back there drive down the road and see what that bag does.....it will go around in big circles for a long time before it actually flys outta the bed.

 

Active thread in progress.

https://www.ford-trucks.com/forums/5...down-open.html

 

ahhhh yes, Click n' Clack, the Tappet Brothers. That's a great entertaining show with good sound technical advice thrown in.

Thanks for the head's-up Dennis.

PS: for you guys with Motion sickness or who own boats, the Mythnbusters also showed Ginger to be a very good Motion Sickness prevention on that same show.

 

Why .... was she popping ....Gravol ?

 

Ahhhh whatever it was: Once you fell under sweet Ginger's spell, a man would forget the Motion of the Ocean!

 

I saw the episode too. But I'm still wondering about tonneau covers. Do they help or do they make gas mileage better?

 

Just Read the other active thread

see the link in Post #8