Pickup tailgate up or down - SAE Studied

[beatr911]

See this link if this iterests you. http://ecow.engr.wisc.edu/cgi-bin/getbig/me/363/ghandhi1/pickup.pdf

Results: Keep it up. Tonneaus MAY help.

[MetroMPG]

Great find! Thanks.

[PaleMelanesian]

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.

[Snax]

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.

[ffvben]

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.

[SVOboy]

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

[Snax]

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.

[MetroMPG]

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.

[VetteOwner]

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...

[2TonJellyBean]

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

[trebuchet03]

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

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

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

[ffvben]

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.

[VetteOwner]

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...

[autocrash]

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

[NH Titan]

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.

[trebuchet03]

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....

[8307c4]

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.

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?

[itjstagame]

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.

[RningOnFumes]

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.

[HAHA]

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...

[Big Dave]

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

[omgwtfbyobbq]

And the best bed cover IMO.
http://img.photobucket.com/albums/1003/thaticktockman/22cc.jpg
http://img.photobucket.com/albums/1003/thaticktockman/58eb.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. ;)

[VetteOwner]

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)

[Improbcat]

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.

[Snax]

And the best bed cover IMO.
http://img.photobucket.com/albums/1003/thaticktockman/22cc.jpg
http://img.photobucket.com/albums/1003/thaticktockman/58eb.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. ;)
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.)

[VetteOwner]

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.

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

[Big Dave]

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.

[trailrunr]

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.

[itjstagame]

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.

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...

[VetteOwner]

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

[lunarhighway]

came across this (http://www.p-szabo.hu/mitsubishi_2006_en.html) 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

[VetteOwner]

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

[Snax]

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.

[101mpg]

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.

[VetteOwner]

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!

[8307c4]

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.

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.

[VetteOwner]

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

[8307c4]

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 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.

[theclencher]

I believe "air meshes" have proven to have the worst aero of all.

[bestmapman]

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.)

This is not a photoshop job. Check out this post (http://ecomodder.com/forum/showthread.php?t=583).

[VetteOwner]

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)

[kamesama980]

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!

cut a 2x6 or 2x8 to fit across the bed in front of the fenders. as wide as the bed I mean. without wight it'll slide down to lay flat but set some sandbags there and viola. in front of the fenders it'll be forward i nthe eddy from the cab and it's low enough not to change much aero.

I have a 87 S10 4 banger. the 2nd gen weighs more and has a piddly excuse for an engine. it weighs about 2750lbs with me and gear in it so a little change is a lot of difference. soon as the cressida gas tank's empty I'll be driving the S10...I calculated 2300 miles to break even just on gas money. 25 city mpg and i can fit an engine, trans, tires, and tools and it won't bat an eyelash at hills. best spent $500 yet :-p

[VetteOwner]

cut a 2x6 or 2x8 to fit across the bed in front of the fenders. as wide as the bed I mean. without wight it'll slide down to lay flat but set some sandbags there and viola. in front of the fenders it'll be forward i nthe eddy from the cab and it's low enough not to change much aero.

I have a 87 S10 4 banger. the 2nd gen weighs more and has a piddly excuse for an engine. it weighs about 2750lbs with me and gear in it so a little change is a lot of difference. soon as the cressida gas tank's empty I'll be driving the S10...I calculated 2300 miles to break even just on gas money. 25 city mpg and i can fit an engine, trans, tires, and tools and it won't bat an eyelash at hills. best spent $500 yet :-p

yea ive had the bags in front of the axel before and it accualy makes driving worse:thumbdown: just weighs down the truck in whole so it slides more yet still spins the wheels like mad.

BUT ive taken the tailgate off and bags out. and taken the car when its snowy:thumbup: but now it snowed so theres like a foot of snow in the bed and thats plenty of weight

i dunno the 2.2L is slow (seems liek a rocket compared to a chevette) BUT its pretty torquey and can haul/tow a suprising ammount.

yea weight in S-10's dont seem to affect mpg that much they do affect acceleration tho

[8307c4]

I do recommend for a tonneau cover spend the $4-500 and get a good one.
I've done experimented with this and it's just a lot of hassle with the cheaper ones.

Mine only cost me about $60 but I spent a quick $20 or so on extra rope because the bungee system wasn't strong enough, then even the rope wasn't any good.

The riveted ones are just as bad for only slightly more, they run you 1-200...
Rivets break over time, every time that cover has to come off you risk breaking one.
Oh yeah, they also like to pop off at highway speeds.

But the biggest problem is aerodynamic down force, and rain!

At higher speeds (50+mph) there is a strong aero down force in the back, most cheaper covers bend under the load, and rather severely so. Then there's the rain, what a pita to wake up after a night of rain and have a cover sunk in full of rain water (hint: It's HEAVY).

I ended up installing a plexiglass sheet under mine, it helps keep it from bending as much but I just happened to have the sheet and even then it cost me another $20 in parts to keep it in place and another hour of my time.

So for the $100 economy cover I have now, I would've been better off saving that towards the 4-500 one, but live and learn, chalk one up to experience.

Get a real one, preferably hard cover but definitely not rivets, something more substantial and spring-loaded that lifts in one piece, something decent.

I believe "air meshes" have proven to have the worst aero of all.

Fair enough, but I have stuff in the bed heh

[Scott]

I also saw the Mythbusters episode where they made made hydro tunnel and said tail gate up was better, but I totally disagree. Back in the 80's I had a Ford Courier, it was a Mazda with Ford badges, an 1800 with a 4 speed. In stock form with the tail up I had to struggle to keep at 65 mph, I always had to keep my foot in it to do anything over 65 mph. The tail gate had 2 pins in it, I could pop the gate off in under a minute. So one day I did, got on the freeway and cruising at 65 was nothing, I could feel my foot farther back from its original buried position. Above 65 felt limitless, 75-80 no problem, mpg went from 28 to 31, I left it off unless I had to haul something.

Now with the bed cap issue, my bed fit a piece of plywood perfectly, it had about 10 hooks on the side, I'd spider web rope around all 4 corners and aerodynamically it acted the same as removing the gate. Mpg range was about 30.

So from my roadside laboratory its gates off or beds covered. Now an area that I don't even know if it will ever be looked at is the underside. Look at all the differentials, transfer cases, gas tanks, mufflers, and frame cross bars just hanging out there. Since trucks are so high to begin with, it seems their natural candidates for belly pans. I like the Bed Wedge of sloaping down from the cab back to improve truck aerodynamics. I think the biggest enemy that makes things like Hummers so unaerodynamic is flat square sides. Take the sander and round off all the edges on modern pick-ups and I think you'll start to see some better f/e.