How to improve fuel economy with a tonneau cover
 

Via autobloggreen.com ...

How to improve fuel economy with a tonneau cover

Full details of their methodology is available, which is nice. (Have to go to the manufacturer's site to read it.)

snug top
 

Darin,hope they didn't go broke buying and burning all that fuel.It's a great thing for them to have done all the testing.And 1.3 mpg at 45-mph really does speak for even better mpg at higher speeds.I've done your famous self-administered head-slap for just getting around to looking at this post at such a late date. Its a significant contribution,should really help the pickup owners, glad I got to see it,thanks much for posting it.

In college, I had a 1995 GMC Sonoma (S10 clone), with a regular cab and short bed (4cyl, 5 speed, 2wd-- totally stripped-down model). I had a tonneau cover the whole time I owned it, and I definitely got several mpg less at highway speeds when I didn't have it on (not that often, but I definitely could tell). With the cover on, and normal driving, I got around 30mpg at 75mph. My all time high was 32mpg, without really trying, and before I ever heard of hypermiling.


But yeah, to keep on topic, keeping the tailgate up is better than down, and a tonneau cover is better still. It's not as good as fashioning a cap into a pseudo-kammback, but every little bit helps.

Actually, this is one of the few things that was done right on Mythbusters (since there were no explosions involved). Tailgate up is, without doubt, better than tailgate down. With the tailgate up, a vortex forms over the bed that sort of acts like a kammback (though not as effective, being normal-pressure air currents). That current does not form with the gate down; driving like that makes your wake bigger and more turbulent.

Yes, it's counterintuitive.

The SAE also has a published paper that proves tailgate up is better.

Wow!

They found out what I found out eight years ago. In a 70/60/city circuit I got a 1.5 MPG improvement.

Anybody wanna buy a nice ARE tonneau?

Nice MetroMPG. I learned a lot of information with this thread. I hope that I can improve fuel economy with a tonneau cover. :D

If a tonneau does not help your pickup,you're doing something wrong.

what if you were to place a piece of sheet metal from the middle of the bed,to the top of the tailgate? The low side would be at the bed and the high part would be at the tailgate.

If you are thinking about it sloping up like a big spoiler it probably won't help mpg. Although, I believe Chevrolet did some testing and found a half tonneau covering the back of the bed was better than a full tonneau for reducing drag. It would have been level with the top of the bed though.

The tonneau cover on my S-10 4x4 saves me a couple of mpg hwy.

I take it off in the winter months so it lasts longer. It's getting old, might have to replace it in a year or two.

Yeah, that's what i meant.The sheet metal would barely lay on top of the tailgate,just level with it.

http://ecomodder.com/forum/attachmen...1&d=1265053166

It seems like wing+cover could be made with very little effort, and also be made so that it could be reconfigured or removed easily if it got in the way of cargo.

I don't see nothing done in the "basic redesign" graph and that has the most effect.what am i missing here?

I think they just used the same picture. Things like rounding the front end (1997 F150), tapering the back of the cab, a lip on the tailgate, etc...

It doesn't really matter to us unless we're in the business of designing trucks.

Basic redesign has the largest range of improvement too, as high as 20% drag reduction down to zero.

Could someone give me an idea of what this roof wing from the chart looks like?

I did this with my old b2200 longbed, it did NOT help any :)

I def saw a huge improvement on my old ranger with a hard cap over open bed.
as I mentioned in another post, driving from my home town (naples, fl) to Miami int airport:
w/o tonneu: 3/4+ tank, just to get there
w/ tonneu: less than 1/2 tank

I made that same trip more than a dozen times over the course of 2 yrs as the woman I was dating at the time was studying in Europe. a few trips were made before getting the tonneu, and 1 trip was made w/o due to picking up a moped. all in all, most of my runs were made with close to the same weather conditions, including wind direction and time of day. as well as our lovely summer storms :p

however, I think all in all, when I get another truck, it WILL be getting an Aeroshell, Im probably going to closely copy that Mitsubishi one that someone posted a link to about 1/2 a yr ago.

Tonneau seems to be the easiest way to gain a small percentage without adding ugly to the aero. IMHO, tonneau or caps add to the looks of the truck, I just can't justify a cap since I often haul things in the bed or in the future will have gooseneck/5th wheel attachments in there, and removing a heavy cap makes less sense to me than a lightweight tonneau.

Hoping it helps, I just bought the cheapest tri-fold I can find, and hoping it adds a little to the whole setup.

The "simple wing" seems to get decent results as shown, but...

I think the "simple wing" could be improved a bit by angling it down slightly towards the tailgate's top edge. The ideal would be a rounded transition going to maybe a 10-12º angle downwards. But even a straight line panel, about 10-12º downwards, should be better than the straight wing.

And of course combine it with the bed cover for a nice improvement.

basic
 

This research was conducted at the time when GM was introducing its all-new pickup design in 1986.The new pickups drag coefficient was around 20% lower than the former design.

That's basically what they've done with the cab on the new F150. It angles down (probably 10-12º) for a few inches at the back edge.
http://image.trucktrend.com/f/264924...unnel_test.jpg

What if the tailgate was lowered halfway down,to a 45* angle?

Seems to me, that would be even worse- because you would be keeping less of that "pressure pocket" in the bed, AND have a big inefficient spoiler... Seems it would be worse than having the tailgate all the way down, but what do I know.

I used to be one of those tailgate down/off/net in its place guys until I tried some semi-scientific stuff of my own, and found that I had a marginal improvement over all else with the tailgate up *in that specific truck*... It only got about 8 mpg (83 F250) and anything other than gate-up configuration would drop it below 8 mpg a hair. Each config measured over several fill ups (and it had about 55 gallons on board).

45-degrees
 

Texas Tech's wind tunnel research demonstrated that the lowest drag was achieved with the tailgate all the way up.It prevents air flowing into the bed backwards from behind,and sequesters a locked-vortex which has a rear terminus closer to the curvilinear path of lowest drag.
The air above the vortex skips over as if the vortex were a solid structure.
You'll notice that current day pickups have a proto-spoiler incorporated into the tailgate.The 'spoiler' performs no function other than help remind the owner to keep the gate up.

According to this video,it shows less turbulence with the tailgate halfway down as i mentioned. http://www.youtube.com/watch?v=ncHDI...eature=related

I don't know what to really make of that last video.

Air with the tail gate all the way up is trapped in a pocket of turbulent flow, which flowing air travels over like a bubble.

Letting the tail gate down half way (45 degrees) releases this trapped pocket of air so that the tufts lay flat, but what of the main flow going over the truck? It is sucked downward, therefore reducing the overall drag?

All it shows is there's less turbulence on that side of the tailgate. What about the whole rest of the truck?

+1 - There's no way to tuft-test this, IMHO, needs smoke in a tunnel...

I'm thinking about putting a sheet of plywood across the rear half of my 6 ft bed ranger and letting a foot or so hang over the gate , any comments or make it flush with the gate, if i let it hang over 1 ft I would be covering 3 ft of the 6 ft bed and one foot overhang , or should I cover 4 ft since that's around 66 % of the bed as per the testing, great advice so far, very promising,

I can't comment on whether or not it is better to extend past the tailgate or not. To do a partial tonneau cover, I believe it is best to separate the covered and uncovered parts of the bed. Basically have a vertical wall at the front edge of the partial tonneau cover, from the bed floor to the height of the cover.

This is what Gale Banks did on his top speed record setting Dakota.
Sidewinder Dakota:
http://www.google.ca/imgres?q=sidewi...9&tx=133&ty=70

Great info, I guess i could try it both ways and check my downhill speed, fortunate to have a good testing area here,

separate
 

In an interview with Sport Truck Magazine,Glen Sharpf,of GM's Aero Lab (patent holder of the 1/2-tonneau cover) reported that some of the low drag performance of the 1/2-tonneau was owed to the opening underneath, back to the inner face of the tailgate.
The low pressure of the locked-vortex captured by the cover is communicated through the opening to the gate.The pressure differential created across the gate,front-to-back, is part of the drag-reducing function.

There is always more to learn, thanks for clearing that up for me. :thumbup:

thank you for the pic! Visually, it looks more like 30*...

The tapered kamm on the cab is from Morelli's most recent work. It works :)

wonder if I just lower the rear spring on the old Ranger a few innches?

UPDATE: 07/23/13

2013-05-16
GMC Pickups 101: Busting Myths of Truck Aerodynamics
2014 Sierra gains fuel economy, quietness from time in wind tunnel
GMC Pickups 101: Busting Myths of Truck Aerodynamics
I say that there are support ribs which disrupt this flow and theory, plus the flutter of the fabric adds air flow distortion. However, I'm not an aerodynamics, so what do I know? I only know what I have seen on my own truck covers.

Some tailgate up verse down discussion the article too.

http://media.gm.com/content/Pages/ne...8668876776.jpg

Mind the gap.

I installed a tonneau cover on my 2000 F150 recently. The ultra gauge tells me I'm getting 0.5mpg less. Hmmm.

Hi. What was your test method?

Don't laugh at me now, I'm completely new to this aero stuff.

I recently bought the F150. Coming from a minivan, the gas mileage is OK. I've had the Ultra Gauge for 4 days now. I'm becoming obsessed with better driving habits, and trying to improve my mpg's. I read this thread earlier, and I had a tonneau cover for the truck, but not on it. I was getting 18.7mpg with an empty bed, tailgate up. I installed the cover yesterday, and today on the same trip to work, I went down to 18.2mpg. I'm driving in a 65mph zone, going around 62, with my eye on the gauge. 60 mile round trip. F150 is the extended cab, or super cab, with a 6.5ft bed, 4.6L engine.

Tonneau cover is a cheapo, canvas cover with 3 aluminum ribs underneath, and two of those are missing.