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Old 07-23-2010, 04:58 PM   #11 (permalink)
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1/2-tonneau

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Originally Posted by gasstingy View Post
Without regard for Mythbusters saying an open tailgate doesn't help fuel economy, I believe it does. I bought a 1992 4.3L V6/Automatic S-10 new and made several trips on I-75 at about 70 MPH. With the tailgate closed (bed empty) I got 19 mpg. With the tailgate down (bed still empty) I got 26 mpg. Both trips using cruise control. My commuting mpg was 21 with the tailgate in either position, speed rarely over 50 mph.

I'd lower the tailgate if I was going very fast until I came up with a better solution. Then there are lightweight mesh "tailgates" that may also show substantial improvement.
Short of a full aeroshell,for your S-10,a half-tonneau will give the lowest drag.
GM fully tested the invention at full-scale,received a U.S.Patent on it,and it was used to set a land speed record at Bonneville at over 211 mph,with Cd 0.31,lower than a Corvette of same year model.

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Old 07-23-2010, 05:03 PM   #12 (permalink)
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impossible

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Originally Posted by gasstingy View Post
Without regard for Mythbusters saying an open tailgate doesn't help fuel economy, I believe it does. I bought a 1992 4.3L V6/Automatic S-10 new and made several trips on I-75 at about 70 MPH. With the tailgate closed (bed empty) I got 19 mpg. With the tailgate down (bed still empty) I got 26 mpg. Both trips using cruise control. My commuting mpg was 21 with the tailgate in either position, speed rarely over 50 mph.

I'd lower the tailgate if I was going very fast until I came up with a better solution. Then there are lightweight mesh "tailgates" that may also show substantial improvement.
I don't mean any disrespect,but your numbers are scientifically impossible.The performance differential separating tailgate-up,vs tailgate-down is only on the order of 1%.
There is a different explanation for your results.
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Old 07-23-2010, 05:08 PM   #13 (permalink)
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10-mpg

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Originally Posted by Skulldragger View Post
Well, I have tried this on 2 different trucks now, the first one was a 2000 Nissan Frontier v6 with tires that were too big for their own good. (looked good though) The tail gate up cost me ~10mpg in EVERY tank of gas I tested. Not only that I could feel the drag difference enough to tell if someone shut the stupid thing for me with out even looking.

With my new truck, (new to me anyway 125k miles) 2001 Chevy Z71 I feel no different but notice that according to the scan gauge I LOOSE 1-2 MPG with the gate DOWN. I was quite surprised but even tested it by stopping and switching it and going back down the same road a few times to make sure it wasn't just me.

I think it just depends on the design of the truck and the way the air flows around it. I think I would have found that the Nissan would have done even better still if I had a full bed cover and left the gate up but the truck was beat to death before I could get around to that and had to be traded off.
I mean no dis-respect,but I'm going to take you to task on your performance claims with regards to the tailgate up/down -10 mpg figure.It's not possible.
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Old 07-23-2010, 05:29 PM   #14 (permalink)
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Meh, you can say what ever you want but I know what the actual numbers show.

See, here is the thing, the Nissan was severely under powered, I used to say it didn't have the power to get out of it's own way. This lack of power amplified any problems as drag increased, causing a feedback loop. At lower speeds it was fine, but the faster you go the worse it gets. My drive to work is 25miles and almost all 70mph freeway so these numbers are correct. Your truck (you do have one and have tried this.. right?) may get better mileage because it had better aerodynamics, a better power to weight ratio, what ever but mine did not. (Man I hated that truck!)

Oh and I mean no disrespect or anything either although some say i sound like i do most of the time.
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Old 07-26-2010, 09:09 AM   #15 (permalink)
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Aerohead knows truck aerodynamics. Trying to argue with him is like arguing with Einstein about physics. I suggest you listen to him.
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Old 07-26-2010, 10:08 AM   #16 (permalink)
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Even Einstein did not argue with the numbers reported by his experiments, he simply attempted to better understand them. I suggest you do the same.
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Old 07-26-2010, 06:53 PM   #17 (permalink)
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numbers

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Originally Posted by Skulldragger View Post
Meh, you can say what ever you want but I know what the actual numbers show.

See, here is the thing, the Nissan was severely under powered, I used to say it didn't have the power to get out of it's own way. This lack of power amplified any problems as drag increased, causing a feedback loop. At lower speeds it was fine, but the faster you go the worse it gets. My drive to work is 25miles and almost all 70mph freeway so these numbers are correct. Your truck (you do have one and have tried this.. right?) may get better mileage because it had better aerodynamics, a better power to weight ratio, what ever but mine did not. (Man I hated that truck!)

Oh and I mean no disrespect or anything either although some say i sound like i do most of the time.
Skulldragger,you're very correct in your assessment that things get really worse speed,and this would be in keeping with the relationship between horsepower necessary to overcome air drag varying with the cube of the velocity.
The thing about the 10-mpg figure is that,when tested at full-scale in the best and most accurate windtunnels,researchers found that the drag difference between tailgate up/tailgate down was only 1 percent.
At 70 mph it takes a 10% change in drag to produce a 6% change in MPG.
Another thing to consider is that on your 25-mile commute,by the time you get to your destination,you've just finally 'warmed-up' all your temperature-dependent systems on the truck.
Too many variables to be able to just point at the tailgate.
If you had or could make the time,you might do the 25-miles for a warmup,then get to the nearest station near the interstate,top-off the tank "completely",then do your test run.I believe you'll see remarkably different numbers.
You'll notice that many new pickup trucks have a vestigial spoiler designed right into the tailgate.The automaker did this hoping that owners would make the spoiler connection,and leave the gate 'up' for better mpg.
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Old 07-26-2010, 07:37 PM   #18 (permalink)
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lol well that truck has since been traded off due to the fact that it could no-longer pull it's self down the road @ 70mph no matter what the mileage. My new truck does not show much if any difference gate up or down.
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Old 07-28-2010, 05:42 PM   #19 (permalink)
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Black Thunder

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Originally Posted by Skulldragger View Post
lol well that truck has since been traded off due to the fact that it could no-longer pull it's self down the road @ 70mph no matter what the mileage. My new truck does not show much if any difference gate up or down.
Skulldragger,hope the new truck works out better.19.1 sounds pretty respectable for a 4X4.That's a full-size truck?

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