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Old 09-25-2007, 05:31 PM   #29
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1992 34' Excella
Austin , Texas
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I saw an episode of Motorweek (I think it was) where they featured a professional racing pickup at a closed track, and they did 5 timed trials of the truck with the tailgate open and 5 with the tailgate closed and the pickup attained the same maximum speed regardless of configuration. This seems to debunk the theory that tailgate open creates less drag.

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Old 09-25-2007, 06:02 PM   #30
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NASCAR has the areo thing down. They know what and what does not cause drag. The closer the back of your pickup is to the front on your airstream of course the less drag and the more important haveing a cap or not comes into play. We are talking about drag and fuel mileage in the end. If you truly want to increase fuel mileage while towing the Airstream of course is the way to tow....not only because of the curves front and rear but because its lower to the ground. The closer to the ground you get with a vehilce the less belly drag. That one reason a 2wd pickup gets better fuel mileage than a 4x4 besides the extra weight of the 4x4 there is less drag underneath. If you want to mess up fuel mileage real bad just put a lift on your truck. ITS NOT just the bigger tires but the increases drag because of the height of the truck. I saw a demonstration of this in 4X4 magazine a few years back. The put a 6 inch lift on a pickup and a set of 37's on the truck...the truck lost over 3 mpg because of the chassis and tire modifications....soo....they then put the STOCK tires and wheels on the truck but left the lift kit on and they only gained back half a mile per gallon. The lowered the truck...and holly grained the full 3 mpg. NOW it don't take a genious to understand it was the drag sucking the truck to the ground when it was wayyyy up in the air to know where the fuel mileage went.

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Old 09-25-2007, 09:35 PM   #31
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2005 25' International CCD
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We can weigh in on this issue. We have a 2005 Dodge Ram 2500 with the Cummings diesel. In fairness I can't tell the difference in fuel mileage. Towing on level freeway at 55 to 65 and under good conditions we typically average 13.5 to 14.5. Head winds and quarter winds, speed, weather and terrain can cause towing mileage to vary between 10 mpg to an ocasional 17 mpg both with and without the shell. However I pulled out the five trips we did in two subsequent 12 month periods.

We pulled our first Airstream, a 22' CCD and then a 25' CCD for about 11,000 miles before we got our cab high LEER shell. Five trips in that time period were:
772 miles, 13.2 mpg (22')
6765 miles, 13.3 mpg (traded 22' for 25' on trip)
1800 miles, 13.9 mpg (25')
622 miles, 12.6 mpg (25')
1037 miles, 13.0 mpg (25'); average for the five trips 13.3.

Once we got our shell we again towed our 25' CCD about 11,000 miles:
6626 miles; 12.4 mpg
650 miles; 12.9 mpg
2126 miles; 14.9 mpg
806 miles; 13.3 mpg
795 miles; 14.2 mpg; 13.1 mpg average for these five trips.

It looks too close to call for me and no significant difference with the upgrade from the 22' to the 25' CCD. However, the shell does give us more security for our bikes, generator, chairs and other belongings in the back of the pickup.
Don (KD6UVT) & Gail Williams

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Old 09-26-2007, 03:57 AM   #32
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Originally Posted by JimGolden
F-105's are cool too. heaviest single seater we had.

My personal favorite is the F-104 Starfighter. The Missile with a Man in it. Stall speed of about 230mph; you have to go faster to take off than a Cessna goes wide open straight down. That's cool! Who needs wings...just put some directional vanes on there and light the burners!
Hey Jim; This human missile almost put me in the grave in 1965. "Boatdoc"
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Old 09-26-2007, 04:30 AM   #33
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1986 25' Sovereign
Allegan , Michigan
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Aerodynamic Drag

Had to jump in with a few observations. Before retirement I was occassionally involved with vehicle road load issues working with various manufacturers. It is NOT a simple issue and sometimes things will suprise you.

One time we evaluated a vehicle with "flip up" headlights that caused a significant increase in road load at 50 mph - other sporty cars were not so bad. In discussing this with an engineer from a car company he said one of the vehicles he tested did better with the lights up.

I have not tested a truck with the tailgate up and down. But another engineer told me they tested a truck with an "air gate" (holes to "reduce" drag but keep stuff in) and it increased road load. I believe that SEMA tested various bed covers and they did improve fuel economy - but their members may have an interest in the outcome.

Several years ago I recall that one truck manufacturer was offering a cover that did reduce drag. Also, another manufacturer had a special version of its half ton trucks that had a lower ride height to reduce drag. They would not have taken those steps if they were not effective.

Finally, aerodynamic drag increases with the square of vehicle speed while tire rolling resistance increases only slightly. Slowing down does help - I think that the current Trailer Life did a test confirming this.

Interesting thread - hope this helps.

Whit Nash
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Old 09-26-2007, 05:33 AM   #34
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The "wall" is about 52 mph. I've forgotten exact figures, but horsepower needed to move at 60 is about 30% more than at 50, and there is a percentage increase per mile per hour over that.
Moral is, if you want better gas mileage, drive slower.
Also, our trailer trails better with the cap on the bed, versus no cap.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.
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Old 01-05-2012, 04:34 AM   #35
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The short answer is . . maybe.

The utility of the pickup truck bed topper is of benefit in and of itself for closed covered storage.

So the shape of the topper is the first item to be covered: Should be "form fitting", that is, follows the contour of cab roof height and bed lines. As if one had built a Suburban-like vehicle, windows or not.

Does a traditional square pickup topper help fuel economy?

But to make the truck "aerodynamic" one needs to follow the "Streamlining Template which leaves a clean wake behind the TV, as with:

Those with a deeper interest:

Tonneau Cover or Cab Extension?

And a topper that shows an improvement of 20%:

Commercially Produced Aerodynamic Pickup Bed Cap

We've more recently covered this topic in Truck Shells and MPG

My best understanding is that one should treat both vehicles for aerodynamics separately as the gap between TV and TT is too large for a combined effect. Big trucks want just 24" between tractor and trailer or less (per aero aids) to reduce or eliminate wind turbulence between them. With a Hensley, the distance between tailgate skin and trailer front skin is 60".

So, an optimized truck will show better mpg while towing, not just
solo. As with the A/S itself: reduced HP demand shows a mpg benefit. And going to trouble to improve solo mpg by driving changes, and some truck spec changes, can underwrite a heckuva lot of vacation travel fuel via savings.


1990 35' Silver Streak Sterling; 9k GVWR.
2004 DODGE Cummins 305/555; 6-manual; 9k GVWR.
Hensley Arrow. 12-cpm solo, 19-cpm towing (fuel)
Sold: Silver Streak Model 3411
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