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Old 05-25-2008, 05:29 AM   #1
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Question Pickup truck cargo separator screen position

I have this cargo separator/window protector screen, and I wonder if I can use it to my advantage for aerodynamic purposes. It can be anywhere in the bed, hanging into the bed or sticking up in the air, though I wouldn't want it up except when I need it that way for loading/protection purposes.

I usually have it in this position (about 14" behind the cab) to let me put small items directly behind the cab:


Right there, I think it probably has zero effect on aerodynamic drag. That area is a low-pressure area. Anything lightweight that I put there gets picked up, flies around behind the cab and sometimes settles back down, but never flies away and becomes litter (though I usually remember to secure that stuff just in case).

Any theories about the best thing I can do with it? Keep it where it is, put it halfway back, or put it ~14" from the tailgate?
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Old 05-25-2008, 10:14 AM   #2
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i think someone did a test regaring tailgate, no tailgate, and with one of those "rally net" gates (plastic things with big holes in em)

can you take off your tailgate and side that thing back into the tailgate position? see if it affects anything...
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Old 05-25-2008, 11:49 AM   #3
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i believe the outcome of the tailgate test was that it's best to have the tailgate up so that there's an air bubble trapped in the cargo bed... still it might be a cool experiment.

what i'd to is measure the height of the separator in the "up" configuration, i assume it's less high then the cab, and than slide it back to a position where the angle of the line from the top of the cab to the top of the separator is 11degrees

sort of in the same way cars like the prius have a fairly high rear to get this angle rather than have the rear slopeing all the way to the ground wich looks sleaker but really isn't. than you might try shifting it forwards backwards see if that does something.

finally you could try to cover the grill with fabric or something to see if that makes a difference... maybe in the 11degrees configuration it would as it would in theory trap a bubble of static air and create a virtual boattail wich slopes down (if it's less high than the cab) and inwards as it's clearly less wide then the cab. i've seen some pictures somwhere that show such a configuraton on a generic object.

you might even considder makeing another one that's even smaller to extend the virtual teardrop. would be practical, wouldn't look that odd, but it might make quite a difference!


also the saab concept 9-X has a spoiler that extends from the back at high speeds... you could have a look at it for inspiration as well
you could even stick some vortex generators on it, althoug i'm a bit sceptic about how some people use them... i've seen them placed in some questionable locations...they're not magic but when used right they do something. wich is direct the flow downwards in a straight line.

happy playing around with it!
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Old 05-26-2008, 06:16 AM   #4
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I am familiar with the tailgate tests, and keep mine up partly because of those results and partly to avoid attracting any attention.

I could remove the tailgate and slide it into the tailgate position, and it wouldn't be quite so bad. I'd enjoy the additional rearward visibility. It might be worth some smoke/yarn tests if I wanted to make the effort.

When in the up position, it sticks up about as high as the window. I don't want to put it up, though. It interferes with my rear view, which is mildly annoying when I'm not hauling anything and should be able to see, and it would really attract attention. When I'm P&Ging on a Saturday night, I probably already look drunk...
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Old 05-26-2008, 08:47 AM   #5
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yea it cant hurt to test it for a tank or so, it might drop but nothing drastic id assume. i ran around with my tailgate down on my truck and it dropped 1-2 mpg.

i coulda sworn i heard that the tailgate net worked the best because it formed a partial air bubble but also let some air out...
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Old 05-26-2008, 11:33 PM   #6
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Mine's a club cab, now yours may not be the same way but on my truck right behind the cab nothing much is happening... However, towards the tailgate there is a strong down force of wind.

Which, on the note of tailgate tests I take it off,
it really doesn't take that long to get it off and
I want the weight gone, too.

I think personally you have to test it with your truck, it may or may not do anything.

Here are my results:
On a 1986 D-250 regular cab doing this did help, noticeably.
On my 1995 D-2500 club cab it didn't do a thing.

Oddly enough the newer truck also has the aero body, the older one was square like all older pick ups. Still odder is the older D-250 got better overall FE than the newer, considerably, and with a carbureted engine.

Such is life.
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Old 05-28-2008, 07:31 PM   #7
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My bet is that the divider would provide a benefit positioned a distance from the cab that is equal to the height of it. This would setup a stationary rolling bubble within that space and provide a smoother transition off the rear of the bed - most likely performing best with the tailgate up, providing it's own discreet zone behind the divider for a second smaller rolling bubble.
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Old 05-29-2008, 06:07 AM   #8
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Now there's an idea I'm willing to try for awhile. Once I establish a baseline for my current strategies I'll try that.
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Old 06-04-2008, 07:39 AM   #9
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Yes, i believe this was an episode of the Mythbusters who tested that the tailgate up was the best way for mileage.

The net would also work. But that was only because there wasnt a tailgate sticking out over the bumper. And since the "bubble" wasnt in the bed anymore, the flat tailgate would be bombarded with the air comming off the roof of the truck causing downforce.
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Old 06-04-2008, 08:37 AM   #10
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IMO they "proved" it for that model of truck in stock configuration only... but... since the 90s truck manufacturers have been trying to design them that way.
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