Pickup tailgate up or down - SAE Studied
 

See this link if this iterests you. https://ecow.engr.wisc.edu/cgi-bin/ge...hi1/pickup.pdf

Results: Keep it up. Tonneaus MAY help.

Great find! Thanks.

If you look at the tables on page 8, the results are different for crew/extended cab than they are for regular cab / long bed. Ext cab - tailgate up, reg cab long bed - tailgate down.

This report confirms what I suggested in another thread, that there is a specific zone behind the cab after which it makes sense to attempt to establish more laminar flow off the rear of pickups. A longer bed, with far less impact from cab length, will benefit more greatly from aerodynamic aids for this reason. I would argue that if one had a bed length nearly equal to the height of the cab to the bed, it would not make any significant difference, tailgate, mesh, tonneau, or whatever because there is virtually no opportunity to re-establish a laminar flow that close to the cab at anything but the slowest of speeds where the impact is nearly nil.

In short, I think it could be argued that longer beds net better aerodynamic possibilities and shorter beds provide less opportunity for improvement. The length of the cab is relatively insignificant.

I just watched part of the re-run of mythbusters on the pickup tailgates. you may loose .02 cd but if the 80+ lbs tailgate is removed wouldn't the mpg go up some if 100lbs = 1mpg. they didn't factor the weight reduction just focused on air disruption.

I don't think that the weight reduction is worth nearly that much. Especially on something as heavy as a truck.

It looks like Ford's lightest F150 is 4670 lbs. So knocking 80 lbs off that nets 4590, or a 1.7% weight reduction. One would be lucky if that translates to even half that much in fuel economy improvement considering all of the time most vehicles spend either cruising or stopped idling.

That's the problem with discussing FE in terms of MPG. A 1 MPG savings on a 50 MPG car is a very different animal than 1 MPG saved on a 15 MPG truck.

Removing 80 lbs might net around 1 MPG in the 50 MPG car. Not so likely on the truck.

L/100 km is better that way.

now i know what I'm about to say has no testing they behind it or any 100% accurate Truth, but i know with s-10's that if you have a toneau cover that you will see a 1-2mpg increase even tho the thing weighs 80lbs(fiberglass with some metal subframe) several people that ive talked to have said they picked up a 1-2 mpg increase with it, not to mention the security and ability to leave somewhat valuable stuff fin the bed. Ive been thinking about making mine out of a steel or aluminum frame with sheet metal as a main covering. i calculated it out and it would be around 60-70 lbs minus the hinges and gas struts to keep it up. cost about half the price of a store bought one.

and yea a truck is meant for hauling stuff. throw oh lets say a 50 lb bag of sand in a car and your gonna notice it, throw it in a truck and it will be like a soda can...

Has anyone with a ScanGauge ever given feedback on up, down, off? Wouldn't take much to try!

I thought they recorded empirical data with the tailgate removed... I'm fairly certain that factored in the weight reduction...

And even more especially at steady state -- not accelerating (unless the mass removed from the vehicle was spinning).

soft toneau cover might be the answer , i installed one on a 07 frontier that had to weigh around 20lbs. but I cant stand those big zippers on it,pulling/tugging to get the end zipped up is a pain.

lol or the evil snap kind! even worse...

Does anyone have any figures with respect to truck caps? I know when I removed mine I didn't get kicked around nearly as much but unfortunately I wasn't keeping track of my FE numbers at the time... :$

On the bright side, I do know that with the cap off and the tailgate up I destroy my EPA numbers, old or new...

Matt

I just added a truck cap to my truck. I checked mpg just before and got 17.8 and then right after and got the exact same. My cap is taller than the height of the truck by about 3-5 inches. It is slanted up at about the same rake as the windshield. I was wondering if the non cab high height would effect mpg negatively but it seems like it hasn't.

It probably has reduced FE compared to a cover that didn't increase the frontal area of the car....

That was my experience as well, my '86 D-250 did get an improvement with the tailgate removed (std cab) but my '95 club cab did not.

Best I can recommend is do your own experiment, mythbusters is entertainment.

As for it up or down, I never understood this concept.
If up is the answer there is nothing more doing, have a nice day.
But if down is the answer then take it off and install an air mesh gate, saves another 20+ pounds of weight, why leave the stupid thing on?

Bah, what a useless study. Why is it the only short beds they had were extended cab and the only long bed was a standard cab?

Does length of cab make a difference?

They studied full toneau or not, but why didn't they try with cap or not, that interests me greatly.

Also why do they continously admonish putting the tailgate down when the 8ft bed showed positive results at anything over 0 degree yaw (and not that bad of a negative effect at 0 yaw either).

I guess I should do my own experiments but without a scan gauge and at my low MPG the variance is so high I doubt there's any real way to tell what helped and didn't.

Mythbusters also tackled this issue. Basically, there is a bubble of air that is trapped in the bed causing the airstream to go over it as if there was something there. So tailgate up is best.

Last year when I was on a working trip to South Africa, I ended up on a race track outside Johannesburg where the local motor club arranged a speed trial open to anyone. They used a radar to measure top speed after the rather long start/finnish stretch. The cars were doing flying starts so most of them seemed to reach "terminal velocity". One of the fastest cars was a very turbo charged Japanese pickup. After a couple of runs, I suggested they should tuck the mirrors in and remove the tailgate to increase top speed. To my surprise, they got significantly lower top speed with that setup (sorry, don't remember the figures). They did try several times but it just didn't work. I never got an explanation to that until I started to read these forums...

A squared-off bed top is the worst setup of all. It is worse than running with no bed at all.

And the best bed cover IMO.
https://www.fuelly.com/attachments/fo...1b12a7775f.jpg
https://www.fuelly.com/attachments/fo...17ef534883.jpg
Could be approximated w/ removable wood sides and a taut fabric cover at the same angle, so the truck can still do truck stuff. ;)

hmm what if you made semi permanent sides and have the part that accualy coveres the bed easily removeable? or what if it were elcamino looking? (kinda sloped down sides but flat toneau cover) im trying to think of a way to make it a bit "stylish" ya know? wher eit can look good custom yet secretly be helping FE(like BBQ up there)

What would be super cool would be a cap shaped like the one in omgwtfbyobbq's post, but with the center section make like a fiberglass tonneau cover. that way when the bed is empty or near empty it'll have that optimal wedge shape. Then when you need to carry something bigger you can open it enough to make it a regular "square" cap shape. Possibly with canvas/vinyl pieces to fill the gap & rear area (like a jeep soft top). that way to get areo when the truck is empty, and the ability to haul more stuff when needed.

Now I wish I had a pickup (& warmer weather) to experiment with this idea.

Who makes that one? We looked all over for something like that.

(Although we have sold our most recent pickup, we will get another to haul our boat.)

hmm that would be useful. liek have the rear hatch fold flat to the underside of the roof an dhave it swing down to make a full topper. and have fold in sides(triangular pieces) so it truley will be a hard top cover

Nice PhotoShop work omgwtfbyobbq. It shows what my fastback fairing would look like rendered in nice fiberglass.

You are clearly better at PhotoShop than I am. Can you make other changes? I'd like to see what my more radical MPG mod would look like.

undisturbed air
 

Dropping the tailgate makes for a large vacumn behind the cab where there was a smaler one before. The air behind the tailgate is much dirtier due to the disturbed air coming from the underbody. dropping the tailgate has very little effect on tailgate air resistance but increases cab resistance. Weight also has little effect on highway mileage but decreases acceleration mileage (city). highway mileage is effected by how much power it takes to maintain a speed more than how much power it takes to get there. GMC found that making a tonneau box fot the front half of the bed increased their top speed in the Sonoma when going for the speed record at bonneville. Making a tonneau box the closes the front half of the bed (level with the top of the bed and squared off down to the bed at the halway point) eliminated part of the bed vacumn without increasing tailgate vacumn. Makes for a handy storage area also. I made one for my '85 S-10 years ago and went from 30 - 32 MPG highway while also helping highway performance, (that 4 cyl 5-speed was quite the dog). It performed more like a '70s vehicle.

Their method was flawed, even the SAE test posted is flawed. There are more variable changes in the different vehicles they used then simply the tailgate on/off or up/down. Why they didn't just use one vehicle I don't know.

Anyway whether it helps or not the best solution is definately a fastback type tonneau which I had planned to make but didn't have $100 to shell out for a snap fastner riveter (anyone have one I can borrow :p? ). I was worried if I'd need an underside frame for it and how taut it needed to be, etc, but BBQs idea is the best and come spring I'll probably try that.

That is: Instead of making a full tonnaeu all sides, etc out of fabric, I can use 2x4s and plywood and make wood sides that slide tightly right into the 3 post holes on each side of my bed and have the tonneae snap onto/over that. It'd probably be less pretty, but certainly more sturdy and pretty easy to make. They'll probably look similar to the Ridgeline but bigger on their own and will probably help on their own to keep turbulence off the sides of the truck from affecting the bed. With the longbed, I plan on going a bit more extreme and openning the tailgate and attaching the tonneau to the open gate (and making the sides to match), should help even more. What I'd really like is something I can slide into the openning between the end of the bed and the tailgate so I can make a half height wall or something so hard acceleration won't have stuff sliding off the bed. Maybe I can make this out of wood too.... hmmm...

i dunno id use the wood sparingly, gets heavy real quick! if ya know how to weld you could weld one up out of small 1"X1" or even 1/2" X1/2" angle iron, strong weatherproof(mostly, i mean the trucks prolly gonan rust and fall apart before the angle iron rusts away)

maybe when its warme rill start designing somehting, i already designed a toneau cover but i dont have the money for the neccessary materials

came across this a while ago. looks nice but probably expensive
there might be benefits to the fairings at the front though...
they don't look as though they would make things worse anyway

in case someone's looking for inspiration

yea i was thinkin somehting liek that (Looks downright fugly on that truck tho)

I think that's a case of makeup on a pig.

I doubt that given the shape of the truck however that the shell really adds much to efficiency.

That's fugly indeed, but I can tell you I got better MPG with a 1998 Nissan Frontier King Cab 2.4 4 cyl with the tailgate down and/or off. Up to 36 MPG hwy at 55-60 MPH, same stretch (Seattle to Los Angeles), same gas pumps, etc. Over 40K miles real-world testing on it.

That tailgate pushed the back end down for more friction guaranteed. On bigger trucks I don't know but that Nissan - every single time.

Wind tunnel experiments don't always get it right - they don't take into account all factors of travel.

ye alike crosswinds, etc.

id like to test the tailgate theory but i have to have sandbags in the bed for winter traction...and yea they do slide around and 3 are up aginst the tailgate....so its a summer testing thing for me...

but if anyone has a 94-97 chevy s-10 (prolly best with the 4banger) that could test for me that would be great!

Agreed, my old 86 standard cab did see an improvement thou I will say I would rather remove the tailgate completely and install a mesh. But on my '95 club cab I am as well if not better off leaving the tailgate in place.

I would further bet it varies from one to the next, you just have to try it and see for yourself, but I do believe either way could work and there is no specific one-size-fits-all solution here.

yea i agree that some trucks it works sone it doesnt, all depends on how the wind comes off the top of the cab

I noticed that too, but my truck weighs something like 3,700 pounds empty and the tailgate itself doesn't weight but maybe 50 to 70 maybe 80 pounds. It's not ueber light but I don't think it weighs 100, I can take it off pretty easily.

Then I have to remove at least 200 pounds to make a difference (400 is more like it), however on a club cab there's always the useless back seat (for some of us), and of course any of an amount of crap we like to carry with us might be best left at home, it can and does add up...

But in and of itself tailgate weight alone is not that substantial, however if you notice an improvement leaving it down then I would recommend removing it entirely and putting in place an air mesh.

This is not a photoshop job. Check out this post.

well im testing no tailagte in my s-10, so far doesnt seem to be making a differance at all(still gets its regular 25mpg in the winter)