Gas Millage?
01-18-2010, 08:40 PM
#31
Senior Member
I'm not sure about the"sheepdip" part, but you are 110% correct on tonneau covers increasing gas mileage on pickup trucks.
A simple test for non-believers is to put bungie cords on the tailgate to hold it close to vertical. Then blast down the highway at 70 mph. Those bungie cords are going to stretch. That is aerodynamic drag trying to lay your tailgate down.
Drive with your tailgate open to get improved mileage. Or better yet, remove the tailgate for better mileage (but maybe not as good as Bondo's "fastback" tonneau).
This is the way my 2010 F-150 4X4 5.4L 3.55 rear end is set up with BakFlip tonneau.
My truck has 1,500 miles on the odometer. Don't trust the displayed MPG. The error range on mine is 17%. That is, plus or minus 8.5% from the real MPG.
I set the cruise control on 65 mph and was "gentle" on the gas and brake when traffic required acceleration or deceleration.
250 miles to Dallas against a 12 to 17 mph headwind (per Sirius weather map). 17.1 mpg
250 miles back to Houston (no wind). 17.6 mpg
A simple test for non-believers is to put bungie cords on the tailgate to hold it close to vertical. Then blast down the highway at 70 mph. Those bungie cords are going to stretch. That is aerodynamic drag trying to lay your tailgate down.
Drive with your tailgate open to get improved mileage. Or better yet, remove the tailgate for better mileage (but maybe not as good as Bondo's "fastback" tonneau).
This is the way my 2010 F-150 4X4 5.4L 3.55 rear end is set up with BakFlip tonneau.
My truck has 1,500 miles on the odometer. Don't trust the displayed MPG. The error range on mine is 17%. That is, plus or minus 8.5% from the real MPG.
I set the cruise control on 65 mph and was "gentle" on the gas and brake when traffic required acceleration or deceleration.
250 miles to Dallas against a 12 to 17 mph headwind (per Sirius weather map). 17.1 mpg
250 miles back to Houston (no wind). 17.6 mpg
Last edited by SailorDon; 01-18-2010 at 08:45 PM.
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imfraser61 (12-12-2017)
01-18-2010, 08:42 PM
#32
Im sure your canopy works like a dream, but tonneaus do not make any difference, and if they do, its insignificant. I have a tonneau and ive driven with and without it, no noticable difference.
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imfraser61 (12-12-2017)
01-18-2010, 08:54 PM
#34
I'm not sure about the"sheepdip" part, but you are 110% correct on tonneau covers increasing mileage on pickup trucks.
A simple test for non-believers is to put bungie cords on the tailgate to hold it close to vertical. Then blast down the highway at 70 mph. Those bungie cords are going to stretch. That is aerodynamic drag trying to lay your tailgate down.
My truck has 1,500 miles on the odometer. Don't trust the displayed MPG. The error range on mine is 17%. That is, plus or minus 8.5% from the real MPG.
I set the cruise control on 65 mph and was "gentle" on the gas and brake when traffic required acceleration or deceleration.
250 miles to Dallas against a 12 to 17 mph headwind (per Sirius weather map). 17.1 mpg
250 miles back to Houston (no wind). 17.6 mpg
A simple test for non-believers is to put bungie cords on the tailgate to hold it close to vertical. Then blast down the highway at 70 mph. Those bungie cords are going to stretch. That is aerodynamic drag trying to lay your tailgate down.
My truck has 1,500 miles on the odometer. Don't trust the displayed MPG. The error range on mine is 17%. That is, plus or minus 8.5% from the real MPG.
I set the cruise control on 65 mph and was "gentle" on the gas and brake when traffic required acceleration or deceleration.
250 miles to Dallas against a 12 to 17 mph headwind (per Sirius weather map). 17.1 mpg
250 miles back to Houston (no wind). 17.6 mpg
01-18-2010, 08:56 PM
#35
01-18-2010, 09:40 PM
#36
Senior Member
Actually it does.
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's.
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?
Did they measure the differential pressure across the tailgate in the up position?
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's.
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?
Did they measure the differential pressure across the tailgate in the up position?
Last edited by SailorDon; 01-18-2010 at 09:58 PM.
01-18-2010, 10:03 PM
#37
Senior Member
I learned from the experts.
That's Jodi holding the smoke wand in the wind tunnel in Allen Park, Michigan.Here is a cool video of Bill Pien, head of Ford Motor Company Aerodynamics, in a very informative video about the aerodynamics of the '09 F150. Bill, Jodi and the whole aerodynamics crew at Ford are a great bunch of people and very smart too.
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Gordon Smith (06-26-2020)
01-18-2010, 10:20 PM
#38
Actually it does.
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's.
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?
Did they measure the differential pressure across the tailgate in the up position?
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's.
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?
Did they measure the differential pressure across the tailgate in the up position?
Im not a genius, but i know my way around a truck ha ha. tailgate down does not work. Ive done it all, tonneau, no tonneau, tailgate up, and tail gate down. and there is no significant difference. numbers may say it works, but experience says it doesnt. maybe your truck is different due to finer tuned aerodynamics, but there is only slight changes in the different configurations with tolerances within various driving habits on my rig. Trust me, any opportunity to save a few mpgs id jump on ha ha.
01-18-2010, 10:40 PM
#39
Senior Member
Actually it does. (1)
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's. (2)
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?(3)
Did they measure the differential pressure across the tailgate in the up position?
Consider that there is a bunch of air in the bed to keep that streamline in your picture rising over the top of the tailgate. That air is under positive pressure. I don't know what that pressure is, but maybe 1/2 psi above the normal 14.7 psi atmospheric pressure.
The tailgate on my F-150 is 64" wide X 25" high. Just a little arithmetic and you end up with 800 pounds of drag on that tailgate. This may only result in .5 MPG improvement if you were to eliminate this 800 pound drag on our relatively inefficient F-150's. (2)
Maybe your truck doesn't notice that extra drag when checking MPG, but mine does.
Your wind tunnel picture, do you have one showing the same test with the tailgate down?(3)
Did they measure the differential pressure across the tailgate in the up position?
(2) How do you come up with this number? Show me some equations and physics as to how you arrived at that number. I highly doubt that even if you are correct that you would see a difference of .5 mpg.
(3) Irrelevant, you already see the smoke clearing the gate with it up. The air flow does not immediately dip down below the top of the cab and immediately hit your tailgate. It just doesn't happen, as evidenced by the wind tunnel test and pictures. On a long bed it might come close, but at speed, the pressure difference is more than likely going to take care of most of that.
Don't you think that if it made a difference we'd have retractable tailgates that move out of the way and were ONLY used when you needed to keep things in the bed? That those responsible for designing new features on trucks would have pushed hard to get that into production because they'd get recognition and maybe a bonus for improving economy which will be a big selling point for trucks from here out?
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marvin1935 (12-02-2012)
