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Tonneau Covers and Gas Mileage

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Old 04-03-2009, 10:08 AM   #1
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Exclamation Tonneau Covers and Gas Mileage

A tonneau can help improve MPG

Mythbusters Testing

I always take Mythbusters episodes with a grain of salt. How many different model and configuration types did they test? What was the weight of the tonneau used.... Mythbusters episode reference: http://kwc.org/mythbusters/2006/12/episode_64_more_myths_revisite.html

Their results actually got the same MPG with tailgate up compared to with tonneau cover. Now account for the weight of the tonneau cover being about 100 lbs and you actually had better aerodynamics but that was countered by the weight of the cover. Effect on MPG will also depend on the steadiness of your speed when adding weight - lots of stop and go acceleration will mean greater effect of added weight. Go with a lighter tonneau like lazerlite aluminum (48 lbs) or an ABS cover (60 lbs) and you will not have so much extra weight to haul around and should get better gas mileage.

SAE Testing

An example of a good SCIENTIFIC test was done by the Society of Automotive and Aerospace Engineers (SAE): http://ecow.engr.wisc.edu/cgi-bin/getbig/me/363/ghandhi1/pickup.pdf

Their testing shows that other variables make a difference such as crosswind and bed length.

For their testing of pre-2004 model F-150s they found:

1. In most cases a partial box cover (at the rear) or full tonneau gave the best aerodynamics.

2. For the 8' bed standard cab trucks the tailgate down but not removed gave better aerodynamics than with tailgate up. Tailgate off gave better or worse depending on how much crosswind compared to speed. Full tonneau gave the least drag in all conditions (best for MPG). Mesh gate gave the highest drag in all conditions (worst for MPG).

3. For the 6.5' bed super/crew cab trucks the tailgate up gave better aerodynamics than down or off (like Mythbuster results but opposite of 8' bed results). Tonneau covers gave the least drag in all conditions with a partial cover slightly better than a full cover (best for MPG). Tailgate off gave the highest drag (worst MPG).

If you look at the flow models you can see that the difference in Cd occurs after the cab, so you could extrapolate that the bed length difference will be the decider in what method you should go with. The GMC and Toyota tested also support this conclusion with their 6.5' bed trucks having similar results to the Ford 6.5' beds. (Tailgate up is better than tailgate down)

In all cases, a tonneau lowers drag...but you have to account for the weight of the tonneau possibly having a negative effect on MPG. Lesson: if you want improve aerodynamics and lower MPG with a tonneau, pick the lightest available.

SEMA Testing

Here is more scientific testing by SEMA showing that tonneaus improve aerodynamics: http://www.trucktestdigest.com/PDFfiles/SEMATonneauStudy2007.pdf

Summary of some of their results:

1. Hard tonneaus did better than soft in general with 6.5% or better drag reduction (hard covers) compared to 5% drag reduction (soft covers) at highway speeds.

2. Reduced drag primarily occurs at above 40 mph and the benefit increases up to 65 mph where it levels off.

3. They also mention that the weight of heavy fiberglass covers can negate benefits.

SnugTop manufacturer testing

Yes, I am including a link to a manufacturer's tests.
http://www.snugtop.com/gas_savings_test.php

Their tests show an improvement of MPG with fiberglass tonneaus. Of note, they did their test with cruise control on which would help minimize the effect of additional weight of the cover.

Last edited by reginhild; 04-08-2009 at 03:33 AM.
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Old 04-03-2009, 10:21 AM   #2
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P.S.: I give permission for copy and reposting of my post above to other forums with the following disclamer at the bottom: "Posted with permission of original author - Originally posted by Reginhild at f150forum.com on April 4, 2009 at 8:08 am MST"

I feel that the Mythbusters simple testing has wrongly spread information that imply hard tonneaus won't improve truck aerodynamics. By reposting the info above with links, hopefully that information problem can be reversed.

Last edited by reginhild; 04-03-2009 at 10:24 AM.
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Old 04-03-2009, 11:59 AM   #3
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Diesel World Magazine Testing

http://www.dieselworldmag.com/content/view/88/37/

They increased fuel mileage on a F-250 diesel by adding a tonneau cover. They also did other mods to increase MPG - note that custom tuning on a diesel typically has a much larger effect compared to tuning on a gasoline engine.

In order of best benefit to least benefit on MPG from their testing:

1. Custom tuning chip
2. Swap to all synthetic fluids (Motor Oil, Transfer Case, Differential fluid)
3. Tonneau cover
4. Exhaust and Intake separately (together they equal the tonneau in benefit)

GM Claims Soft Tonneau gives 0.5 MPG improvement

http://www.popularmechanics.com/blog...s/4307082.html

Popular Mechanics Testing in 1982 showed MPG improvement with tonneau

...anyone have access to this article or an old copy of the magazine?

West New England College Tonneau Testing

Link to results republished by Leer: http://www.moryinc.com/images/Improv...%20Mileage.pdf

This study on a Dodge Ram pickup showed a 1.18 mpg increase in fuel economy with a Leer tonneau. Removed tailgate and cargo net tailgate both showed decreased fuel economy.

Last edited by reginhild; 04-03-2009 at 12:41 PM. Reason: added another reference
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Old 04-04-2009, 02:20 AM   #4
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p.s.: here is a link to the thread that caused me to start this rant:
https://www.f150forum.com/f4/i-knew-mpg-were-going-decrease-but-sucks-20705/
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Old 04-04-2009, 10:58 AM   #5
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I know when I had my 2001 Ranger Edge with flair side bed the soft cover gave me 2 mpg improvement.
I have not put a cover on my 07 FX2 yet......jury still out on this one.
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Old 04-04-2009, 10:08 PM   #6
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This PE Jackrabbit cover probably saves about a half mpg.
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Old 04-06-2009, 01:50 AM   #7
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OWNERS - post your MPG improvements with a tonneau cover HERE in this thread!
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Old 04-08-2009, 03:35 AM   #8
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Hello all. This is my first post im a newb and id like to thank everyone for their helpful threads. I have got some GREAT info from this site and I hope to do the same for all of you in return.

I recently purchased an 09 f150 platinum and I am obsessed with it. My average mpg was 15.1 to 15.3 depending on my driving. I added a tonneau cover (bakflip g2) and I put nitrogen in my tires and now my truck is at 16.1 to 16.3 I was very impressed that I got 1 mile better out of the gallon with that combo and the nitrogen was cheap it was only 40$ from my local ford dealer. Most of you im sure have covers but the bakflip works great!
I Hope this helped some having complaints about their mpg.
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