Have any of you seen a real world fuel mileage increase by adding a tonneau (sp?) cover/flat pickup box cover? I'm adding one to my 2011 Ram for other reasons, but I have heard that putting one of these on does help highway mileage. What have any of you seen? True or another urban legend? I remember when those nets on the back of trucks to replace the tailgate were all the rage, but then read a few years later that they didn't really help at all...?

JS

I never saw any increases or decreases on our three trucks.....But we do mostly around town driving. On the highway you may see a very minor difference IMO.

I put them on to keep the weather and prying eyes out. It really bothers me around here to see pickup beds full of snow. And it's nice to know you can stick something in the back and have it stay dry to mostly dry--depending on the cover and actual weather.

That's why I'm adding it to mine, to be able to keep stuff in the bed and keep it dry. Just curious on the mileage, and I'm driving this truck around 100 miles a day or about 500/week, so maybe it'll save a little gas to boot?

JS

That said, if I saw an average of 1mpg improvement, that would be very cool!

JS

I don't have a tonneau cover but I do have a camper shell.. I also read where camper shells would help fuel mileage but after taking four grown men to lift this thing up ,I'm saying no way it could help fuel mileage.. I'm sure just the cover is not near as heavy as my camper shell.. But anyway, I think you will love the cover for its purpose. I can't imagine not having this shell to keep all my hunting gear and tools dry and out of sight...

I`ve always had bed covers on my trucks for the same reason to keep the elements out, I don`t know if there is really a gas mileage difference, heres a not so funny story about the elements and pickup beds: A few years ago at my local track there was a quick passing shower resulting in down time and a track drying process which took an hour or so,the first vehicle to make a pass after the drying was a pick up with a bed liner and no bed cover, you guessed it when he left the line all the water in the bed from the rain came out the back all over the starting line, the track personal were not amused.

On my 72 d100, I have a leather snap on tonneau cover.

It might be my suspension, but my truck drives better with it off. With it on, I could feel my back end wriggle around while driving. With it off, the truck tracks straight.

No real mileage increase. Or decrease though. With the 318, and a230 3 on the tree, it would get real close to 20. Went with the a833od and the tonneau cover it got the same haha. But I also "upgraded" to a 4bbl.

I imagine with a hard cover, it would be different. I stopped driving with my leather one. With the tailgate up, its been shown that the tailgate catches a very tiny bit of air, which rolls over/back towards the cab, which allows the rest of the air to roll over the truck. Ever drive with leaves in the bed, and the rear slider and sunroof open?

I'd guess a long bed and a short bed truck might have different results with a bed cover. My truck is a short bed. I saw no measureable difference in mileage with the cover. The truck now has a topper on it. Little to no difference with that either. How it's driven only makes a small difference in fuel mileage. It's a 100% genuine gas hog!!

I saw video's of different year Dodge Rams that were in an air tunnel and the smoke didn't even come close to the bed, so I doubt that adding a bed cover would do anything. I have had them and full size caps on my trucks but never cared about mileage difference so I never checked.

on a 1995 Ram ClubCab with a 6.5 foot long cargo box i got a 1 mpg increase on the highway with a hard ARE tonneau

there was no increase in city driving

US Patents are sworn to "under oath"

GM swore under oath that the best aerodynamics comes when you cover about half the open bed from the tailgate forward.

See this patent

http://www.google.com/patents/US4573730?...ved=0CDUQ6AEwAA

this drawing and graph shows the effect

http://patentimages.storage.googleapis.com/pages/US4573730-1.png

there is also a good study of tonneaus on full sized GM and Ford pickups in the large wind tunnel owned by the Research Council of Canada, but unfortunately they did not include a Ram pickup

Back when I had my 2002 Ram 1500, I put a vinyl bed cover on it. It was one of those that had a frame with cross bars it secured to. I didn't have to undo anything to drop the tailgate which was nice.

The one thing that surprised me about the cover was how much it moved. Even after sitting in the sun, it almost took two people to install it was so tight. Yet, out on the highway, in a strong crosswind, that sucker flapped around as if it wasn't fastened.

Either way, mileage didn't change.

My Extang cover is like that as is all the covers I`ve had in the summer they are fine but in the winter they are hard to put back on after removal for cargo, My Extang has moving snap bases and even with those its hard. I try not to remove it when its cold but the looks and purpose out weigh the disadvantages.

Mythbusters tested several combinations on a dodge pick-up.
Same mileage with tailgate up, or using a bed cover.

Only gain in mileage was using a mesh tail gate.

Ron

http://mythbustersresults.com/episode64

no difference on the 3 trucks we have put them on.

I prefer the extang solid fold cover...
http://tonneaucoversworld.com/extang-solid-fold.aspx
it is easy on /off you can open and close the tailgate with opening the cover.

MythBusters did a segment on them.They used covers,open,the tailgate straps with holes etc.IIRC the best mileage came from just running it stock.Google it and it should come up.Rocky

No gains here with a light vinyl bed cover

Notice that Mythbusters started assigning Grant to do the Fuel Economy testing after Adam thoroughly messed up the test using the Dodge Dakota and the "FlowScan" brand meter?

I have had two Flowscan meters on boats and they definitely cannot be calibrated well enough to measure tenths or hundredths of a gallon like Adam tried to do.

Adam and Jaime needed to have done tests long enough to get differences of full gallons, which would have involved long distances, like they did with the tailgate up/tailgate down test of the F150 pickups.

Jaime already has truthfully told us TV viewers that he finds pickup MPG tests too boring.

It may be that a mesh tailgate substitute may provide better MPG.

A mesh with the right size and number of holes
MIGHT retain the "horizontal whirlwind" behind the rear window
while reducing the low pressure area right behind the tailgate.

The GM US Patent above seems to hint that
a partial bed cover
allows a horizontal whirlwind to form in the forward section of the bed.

Those odd slanted bars on Avalanche pickups are there to modify the horizontal whirlwind,
as are the slanted sides of the Honda Ridgeline.

an empty bed with the tailgate up looks like an air dam to me---you might try a test with the tailgate down or taken off vs with what you have with it up...

Zero change in my MPG after installing a Gem Top hard cover, which is very heavy, on a 97 Ram 3500 V-10.

http://www.roadandtrack.com/go/news/new-technology/keep-that-tailgate-up-mostly

sample quote

Indeed, there was one case,
a 2001 Ford F-150 standard cab,
where lowering the tailgate actually improved CD, albeit insignificantly, from 0.5230 to 0.5215.
(And, yes, pickup trucks are bricks aerodynamically.)

In their report (SAE Paper No. 2004-01-1146),
the researchers discussed underlying reasons for the phenomena.

In general, there's a wake immediately behind any pickup cab, and this suction is greater without a tailgate in place. True, presence of a tailgate adds a small drag increment; but the cab wake predominates.

more info:

http://www.nrc-cnrc.gc.ca/eng/achievements/highlights/2007/tailgate_down_myth.html


http://papers.sae.org/2004-01-1146/

Had a 94 F150 supercab 4x4 about 12yrs ago and drove 45-50 miles to work one way.

Added a tonneau cover, flowmaster catback and K&N drop-in and gained 2mpg highway.

when people ride in the back of your truck bed they find out sitting behind the cab equals dirt in your eyes---riding near the tailgate means cleaner air---so there is a big swirl of air disturbance right behind the cab--maybe an air dam on top of the cab with no tailgate would let air slip by easier....bob

I have a Leer tonneau that I have stored on jackstands. The dang thing weighs at least 300 lbs. There is no way that this thing could make the truck aerodynamic enough to offset its weight.

The high efficiency Ram uses a tonneau and running boards. They did not add them for appearence.

UPDATE:

I added a soft/folding tonneau cover last fall, mostly just to keep the bed clean and the ability to put stuff in back and keep it out of sight/locked tailgate. I haven't watched my fuel mileage that close lately as it's been SO COLD out here that I'm spending a lot of time letting my Ram idle outside to warm up, so my mileage hasn't been great day-to-day.

That said, on Monday and Tuesday I had to drive (for work) over 140 miles each day, all interstate, and decided to check my mileage. So, I filled up at home, drove this trek two days in a row, and filled up at home again. I clocked a 21.9mpg trip with my 2011 Ram 1500 Quad Cab 5.7L Hemi 4x4. I was impressed! I never got that kind of mileage before adding the cover. Now, I don't want to say that the cover did this...but, I was NOT driving these two days in any way to increase gas mileage. 65mph zone, I was treking in at 75-80 most of the time trying to get there quicker...

I'm very happy with the bed cover, and it's certainly not HURTING my fuel mileage!

Thanks for all the replies! I really think that it helps, I don't really know how much, but every little bit counts at these gas prices and the amount of miles that I drive.

JS

Years ago a truck magazine did this comparison on a Chevy, Ford and Dodge. Only the Dodge saw improvement with a bed cover. I want to say it was in the '02-'08 body style if that helps.

The three way comparison of Snugtop tonneau's done in conjunction with SEMA can be read about here:

https://web.archive.org/web/20061003133109/http://www.sema.org/main/semaorghome.aspx?ID=55785

One key point to note is that
the three pickup trucks were only allowed to circle the racetrack at 45 mph
because they did not have fitted internal rollcages,
like the racetrack's liability insurance required.

That is a shame because a test at 75 mph would have more clearly shown the difference in aerodynamics

More from SEMA on tonneau aero on Dodge Rams here from some ASME prize winning engineering students at Western New England College:

https://web.archive.org/web/20050313154211/http://www.sema.org/Main/SemaOrgHome.aspx?ID=52546

A Ford Engineer on how bed covers affect F150 aero:

https://web.archive.org/web/200306031606...s_save_fuel.htm

sample quote

"Tonneau covers on pickup boxes reduce aerodynamic drag"
said Ford's Jack Williams.
"we've seen reductions of about 8 to 10 percent on the F150, which means the average fuel economy improvements for the EPA city/highway cycle(test) is about 2 percent.

"The average steady-state (cruise control) fuel economy improvement at highway speeds is close to 5 percent.."

end quote

On an early walk this morning i saw one of these "Slimline" bed covers on a Chevy pickup and wondered whether the "stepdown" at the halfway point had any aerodynamic effect, considering the US Patent from GM posted above.

http://www.slimlinetruckcovers.net/

The Slimline designer does have aero in mind because there is a mild rear lip spoiler that is difficult to make out in the photo.

On a smaller scale the Rampage topper
made the truck more stable at speed

without it the truck would move around
when big rigs, would blast pass it
on the interstate



at the track it also help the aerodynamics