>Aerodynamics testing has revealed that having the tailgate
>in the open position stabilizes the airflow as it flows out
>the bed of the truck. Removing it causes a lot of turbulence
>and increases drag.

Now that seems to make sense!

Interesting link, but what do they mean testing with a "water tunnel." These are trucks, not boats!

So a modern cap is best, a tonneau second best. I'll stick with the tonneau as I don't want my pickup to start looking like an SUV!

 

The results of that study sound reasonable, though we have to remember that they don't necessarily apply to all pickups - each brand is different, as is each body style (longbed, shortbed, newer trucks vs. older trucks).

In my experience, lowering the tailgate (or even taking it off) doesn't seem to make much difference one way or the other - especially on newer trucks. On some older trucks the difference might be noticeable - mainly because they were designed before modern aerodynamic testing was in common use (at least for trucks), and the flow over the cab and bed wasn't very smooth.

The only things I've seen that reliably make a difference are tonneau covers (which almost always help, at least a little) and caps (which almost always hurt, at least the squarish ones). The extra-tall caps are the worst - I've seen them cut mileage 25% or more. My neighbor put one on his new F150, and he went from 15mpg to 12mpg in identical driving conditions...but he likes the look of the cap, so he's keeping it on there (for now). The custom-made cap in the study is interesting...I think it looks pretty odd, but if it gave me 3mpg more I might be able to put up with it. Some of the new caps are more rounded and are starting to look a little like the one they made up for the test - and maybe those would actually help a little, I dunno. However, I regularly haul hay and feed - so if I had a cap or cover I'd be taking it off all the time. I do sometimes take the tailgate off, but mainly when loading and unloading heavy objects - because I've ripped them off before, and it wasn't much fun.

The tailgate nets never made sense to me at all, even back when they were introduced. They aren't strong enough to hold stuff in the bed, so they don't work like a tailgate...and they mess up the airflow, so they aren't as good as leaving it down or taking it off. The worst of both worlds?

My advice would be that with a newer Ford truck don't bother messing with the tailgate - but if you have an older one (1980 or earlier) it might be worth putting it down just to see.

LK

 

Hopefully someone can help me here....I know there is a scientific term associated with the gas / fluid flow events occuring along the trailing edge of automobiles. It deals with pressure recovery and the tendency of the gas (in this case - air) to follow the surface along the trailing edge. I remember reading an article some months ago that described this phenomenon, and explained how adding a small spoiler (like that on the back of a Taurus) can minimize the negative effects of this phenomenon and accordingly reduce drag by minimizing the low pressure zone behind the vehicle. Net effect: better pressure recovery and lower Cd.
Coriolis effect keeps coming to my mind, but that ain't it, although I think it was a word similar to "Coriolis". Anybody know???
I've run my truck Tailgate up and Tailgate down and can't say I've seen any real difference in mpg. I am GUESSING that with the tailgate up, the air "trapped" in the bed acts as an aerodynamic aid by forming a smoother "surface" for the air flow as you drive down the highway. I have seen napkins float around in the bed for FAR longer than I would have expected (with the tailgate up) leading me to believe that the air in the bed is somewhat static. I am also GUESSSING that dropping the tailgate eliminates this pocket of trapped, static air and now we are left with the net effect of air flowing over the hood, then the top of the cab, then BAM! a flat surface on the trailing edge (the rear cab window). Very bad for gas flow, very poor pressure recovery, creates more drag.
In short, I'm guessing science might just prove "common sense" to be in error.

Another thing that concerns me...I have seen in my rear view mirror, people coming to a stop behind me. By the look in their eys, I have seen them suddenly realized "Uh Oh, there's a tailgate there, I gotta stop NOW". I rarely travel with my tailgate down now, especially in traffic. Not worth risking a mashed tailgate.

Brian A

 

[updated:LAST EDITED ON 24-Jul-02 AT 03:09 PM (EST)]I have had people tell me that gas mileage was definitely worse with the tailgate down.

I have read several articles that showed there was no difference.

My theory is that you don't know what your gas mileage is unless you fill up every time for a long time and take an average. My mileage (on all my 5 vehicles) varies up to 20% without making any changes. Depends on too many factors, such as the quality of the gasoline, weather, traffic congestion, etc.

I don't understand it being against the law to drive with the tailgate down. How else can you haul 8' lumber in a short bed? That would just about eliminate 50% of the use for the truck, especially in Texas.

But I do hate to see pickups in front of me with the gate down and loose junk in the bed waiting to fall of in front of me.

EDIT: Sorry to repeat some previously posted info. I didn't realize there were more pages when I posted.


Winford

 

hey y'all, try this, take a ride, in the back of your truck, with someone else driving, (no-brainer on this one, lol)
with the gate up, and see (read: feel) what he wind does, it blows back up toward the cab, then goes UP, thereby giving the oncoming wind a "spoiler" effect, and making no big difference in fuel economy, or so it seems to me, so from now on my 'gate stays UP...lol

 

 

[updated:LAST EDITED ON 28-Jul-02 AT 00:51 AM (EST)]I feel so lucky not having this problem. If I had a tailgate I would probably leave it up, as I have noticed open ones bouncing way too hard, that cannot do anything any good. The wind on the flatbed is a little strange in behavior - I have forgotten to replace my fuel cap a few times, and left it placed on the bed. First time I did it, I found out 5 miles down the road, and the cap was still on the bed. The second time it was there for 460 miles - I found it when I refueled. I have not yet had to replace the caps, so a flat bed does not have much wind blowing around on it, leastwise not at the front. (my filler caps are at the fore end of the bed, above the bed, mounted on the chain well.) This has next to nothing to do with tailgates, but I wanted into the conversation.


Wm
'96 F450 White with Grey interior Crew Cab. Banks Turbo, Intercooler and Exhaust,
Power pack Chip, shift kit, Auxiliary transmission, electronic enhanced transmission control,
16 forward and 4 reverse ratios. 340hp 660ft lb 4 wheel drive, 4.10 gears, 12,ooo# winch

EDIT:

why is the word tailgate a link, and why the figure 460???

 

haha i always forget to put my gas cap back on

 

i always forget to put my gas cap on, your not the only one.

 

>hey y'all, try this, take a ride, in the back of your truck,
>with someone else driving, (no-brainer on this one, lol)
>with the gate up, and see (read: feel) what he wind does, it
>blows back up toward the cab, then goes UP, thereby giving
>the oncoming wind a "spoiler" effect, and making no big
>difference in fuel economy, or so it seems to me, so from
>now on my 'gate stays UP...lol

See, most of us city folks never ride in the back of a pickup to get a practical experience like F_150_hotrod did. (Riding in the back was outlawed in Dearborn Michigan due to a wild teen rolling a truck with a bunch of partying high schoolers in the back, maiming a few and I believe killing a few too.) So it seems that the air piles up in the bed with a closed tailgate and then acts like a aerodynamic bubble to shoot the oncoming air over the gate.

 

My last trip to the dragstrip I made 4 runs with it up and 4 with it down. I ran the same both ways.

 

When I was driving my 94 Ranger 4 cylinder 5 speed The truck was much faster with the tailgate down on the highway. I dont remember the gas mileage but I get about 1.5 mpg better with my 98 Ranger , 4x4, 4L auto with the AC on and the gate down. I have never been stoped for having it down and have put on 16,000 since last Aug.

 

I think the best design is a fastback truck. From the cab top, sloping down to box height at the very back. I am sure this oughtta do something for aerodynamics. You really need to get about 10 heavy smokers to jump in the back of your pickup and tell them to light up. Then hit the road at about 60 mph and see what the smoke does. Does it swirl in a horizontal tornado, or does it glide gracefully out over the tailgate? Now, try it again with the gate down, but with menthol cigarettes. (I know, changing two controlling factors at once is not very scientific, but at least no one will want the rest of the pack you have to buy! LOL)
I have one of those caps that starts off at cab height, then slopes up a few inches. Never tried economy before the cap went on...
Oh, and I know Jesus loves me! Amazing, but true!
Mark



https://www.ford-trucks.com/user_gallery/displaythumbnail.php?&photoid=5362&.jpg
Ford started it; Ford will finish it!

 

while reading the first few posts i was also thinking that the air inside of the bed gets trapped by the flowing air over it (well i guess its not flowing, rather the truck moving through it) and creating a sort of air bed cover.

the dudes smoking in the back of the truck is a great idea.

 

I have to agree with it tearing the truck up running with the tailgate down. It gives the box sides more room to flex and doesn't do squat for milage. I wouldn't worry about the pivots too much. they take a beating regardless. If The cables snap though it is a great way to customize the tailgate. lol.

Brad Godkin
1986 F350 XLT
CC/SRW 6.9 auto