1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

12 MPG? Can't I Get Any Better!?!

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  #46  
Old 03-10-2006 | 11:23 PM
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Andyman8282
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I hate to state the obvious, but how exactly could the tailgate down make the truck less-aerodynamic?
 
  #47  
Old 03-10-2006 | 11:23 PM
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68Mercury250Ranger
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From: gravel road ONTARIO
I bought 3 new trucks in my past. 1989 F150 shorty 4.9 M5OD 2wd with 3.08 gears, 1991 F250 2wd 7.3 E4OD with 3.55s ,and a 1996 F250 SC shorty 4x4 PSD ZF 3.55s.
I always calculated my mileage for all 3 . Summer and Winter MPG were extremely different. 89 averaged about 21mpg summer/winter combined up to 28 on highway trip at a steady 70mph, heavy loaded down to almost 12mpg.
91 was a little better on fuel pulling unless I took it out of overdrive like the manual says. Averaged around 19.5 mpg , but best was almost 25mpg empty highway.
96 was almost identical to the 91 but got 27.5 on long trip empty in summer. It could pull 12,000 lbs and at 70mph, which neither of the others could.
All 3 ran at almost the same rpm at 70mph 2100.
I did all my calculations with an Imperial gallon 4.54 litres, US gallon has only 3.78 litres
Now I am married , 2 kid under 5 with a stay at home mom and a mortgage.
My driver is a 86 VW golf diesel, and the old trucks are just summer toys.
Old Fords Rule, I have 2 barns full.
 
  #48  
Old 03-10-2006 | 11:31 PM
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68Mercury250Ranger
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From: gravel road ONTARIO
Oops , forgot to throw in my 2cents on the tailgate thing.
When empty and highway commutting, all 3 trucks were slightly more fuel efficient, the 89 F150 would gain almost 2mpg, the 91 and 96 were better but just over 1mpg difference. When pulling my trailer it got worse mileage on the 96 if I put the gate down, would drop 1-2 mpg.
But it doesn't look cool when you can't advertise the FORD badge.
 
  #49  
Old 03-10-2006 | 11:44 PM
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Bdox
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Originally Posted by Andyman8282
I hate to state the obvious, but how exactly could the tailgate down make the truck less-aerodynamic?
Aerodynamic and truck are contradictory terms. However, having the tailgate down actually increases turbulence, which increases drag.
 
  #50  
Old 03-11-2006 | 01:40 PM
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little Loopie
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I lurk around in the shadows on here alot more than I post............


I'd like to hear more info on the 'mythbusters' test. I must have missed that show. Did they use the SAME truck or 2 different trucks for testing, or did they do what they did when they tested the AC Vs. Windows down? For that they used a AWD explorer and a selectable 4wd one. SO, this ALONE would affect there roundy-round comparison they did as they didn't test for a decline in mileage, but which one did more laps. I've never tested the diff. between the 'gate up or down, but was raised to ALWAYS drop it do to, "wind cresting the cab and ramming into the 'gate"? It just seems logical to me.........


Hmmmmm........I just went back and read that linked article, sounds like a good one to sell tonneau covers and canopies......but the leaves/paper cup comment was worth thinking about.
 

Last edited by little Loopie; 03-11-2006 at 01:53 PM.
  #51  
Old 03-11-2006 | 02:08 PM
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Not quite sure what trucks they used and if they used different tests. My girlfriend is the one that watches TLC all the time. I had my tailgate down one afternoon, and she put it up, explaining the show to me. I just took her word for it
 
  #52  
Old 03-11-2006 | 02:46 PM
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Bdox
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The tailgate thing:

Think about an airplane wing. The shape of the wing has a longer surface over the top which makes the air speed up to pass over it. This creates a big pressure drop, which in turn creates lift over the wing and the plane rises.

The roof of your pickup is the top of the wing. As your speed increases the air rushing over the cab causes a negative pressure behind it, which tends to pull you backwards. Having the tailgate up maintains a rolling cushion of air in the bed, out of the overall airstream. This air cushion is affected by but not a part of the overall airstream. Dropping the tailgate bursts this bubble and the whole bed then becomes a mass of turbulance that creates a greater negative pull on the truck.

Try this: Before your next wash job, sprinkle a pound of flour all around into the bed and have someone drive your truck with the tailgate up. Watch what the flour does. You will see the air cushion in the bed. After you observe the pattern, stop and lower the tailgate and see what it does then.
(Keep all your windows closed for both tests.)
 
  #53  
Old 03-11-2006 | 03:47 PM
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little Loopie
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Originally Posted by Bdox
The tailgate thing:

Think about an airplane wing. The shape of the wing has a longer surface over the top which makes the air speed up to pass over it. This creates a big pressure drop, which in turn creates lift over the wing and the plane rises.

The roof of your pickup is the top of the wing. As your speed increases the air rushing over the cab causes a negative pressure behind it, which tends to pull you backwards. Having the tailgate up maintains a rolling cushion of air in the bed, out of the overall airstream. This air cushion is affected by but not a part of the overall airstream. Dropping the tailgate bursts this bubble and the whole bed then becomes a mass of turbulance that creates a greater negative pull on the truck.

Try this: Before your next wash job, sprinkle a pound of flour all around into the bed and have someone drive your truck with the tailgate up. Watch what the flour does. You will see the air cushion in the bed. After you observe the pattern, stop and lower the tailgate and see what it does then.
(Keep all your windows closed for both tests.)
Ahh, yes, it does make sense. Just backwards to a "standardized" thaught process............I've just always seen the 'gate dropped for highway my whole life by my old man. Thanks for the clarification of the "cusioning affect".

Mike
 
  #54  
Old 03-21-2006 | 09:59 AM
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countryboy4_1qt
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Your mileage greatly depends on what gears you are running. I have a '93 supercab 4X4 302/3.55 and 12 mpg for me is GREAT!!
 
  #55  
Old 03-21-2006 | 04:52 PM
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That post above about the turbulence...and the airplane analogy...that explains it all.
That sounds like the end of the tailgate arguement
 
  #56  
Old 03-21-2006 | 05:12 PM
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quicklook2
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these are full size, heavy even when empty, not really aerodynamic trucks.

up or down tailgate or fast or slow speeds they will never get very good mileage.
 
  #57  
Old 04-16-2006 | 11:40 PM
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Bryan Baxter
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Explain the tire size fuel economy please

Explain the tire size fuel economy please for me.


Originally Posted by dale gribble
Oh yeah- don't foget to take into account tire size... Even if you went from a 235/75R15 (28.8" diameter, 90.72" circumferance) to a popular replacement tire that most people put on- a 31x10.50R15 ( most measure ~30.5" diameter, 95.61" circumferance)... That's a 5.6% difference.

12 MPG * .056 difference= .67MPG difference. That brings you up to almost 13mpg! for free!

If you need to know the tire size your truck shipped with, it's in the door jam. Do the math if you have done a tire size change.
 
  #58  
Old 04-17-2006 | 12:28 AM
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Bdox
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If your tire diameter is larger, you travel slightly further with each revolution of the tire.
 
  #59  
Old 04-17-2006 | 01:16 AM
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Bryan Baxter
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okl but how would that translate to better mileage? Wouldn't the increase in tire size require more energy to turn due to weight?
 
  #60  
Old 04-17-2006 | 08:36 AM
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CABROCK
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tail gate down laws

So, I can't got to lowes and buy (10) 2 x 4 x 12' and load up the truck and drive home cause I got the tailgate down!

Originally Posted by nola45
One final thought on leaving the tailgate down. It is illegal in every state in the union.
 


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