MPG---- Tailgate down vs Tailgate up
Rookie
Joined: Nov 2005
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RE: MPG---- Tailgate down vs Tailgate up
I have a soft tonno cover and to tell you the truth, my onboard computer shows a worse mpg reading, i used to get about 14 at about 55-60 mpg but now its around 12...i dont get it, it said that it should help wit mpg. maybe my toolbox is creating a different airflow patern causing me to loose mpg?
Record Breaker
Joined: Feb 2005
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RE: MPG---- Tailgate down vs Tailgate up
If I was very concerned with MPG, I'd have bought a rice burner
LOL! Seriously though, I drive city 90% of the time and my mileage sucks ****. I get better MPG towing my parent's boat down the highway at 65-70 than stopping and going in traffic every day. Thankfully the gas prices have gone down to around 2.40 down here.
LOL! Seriously though, I drive city 90% of the time and my mileage sucks ****. I get better MPG towing my parent's boat down the highway at 65-70 than stopping and going in traffic every day. Thankfully the gas prices have gone down to around 2.40 down here.
Champion
Joined: Aug 2005
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RE: MPG---- Tailgate down vs Tailgate up
If you want to see an 'attached vortex' of wind behind the rear window of a Dodge Ram,
unlatch your toolgate box lids and watch them bob up and down as you drive on a smooth road at 70 mph. My dad and I watched this on a Dodge Ram in front of us on I95 some years ago.
The vortex (tornado like wind) builds up stuck to the rear window area, but then 'detaches' every 10 seconds or so. This change cause the toolbox lid to jump up when the vortex detaches.
This is the same thing that causes those stop signs to violently twist back and forth in hurricane winds.
It is also what makes trees sway in the wind.
You can also see this in fog - but following to close to a vehicle in front of you in foggy is certainly a bad idea.
unlatch your toolgate box lids and watch them bob up and down as you drive on a smooth road at 70 mph. My dad and I watched this on a Dodge Ram in front of us on I95 some years ago.
The vortex (tornado like wind) builds up stuck to the rear window area, but then 'detaches' every 10 seconds or so. This change cause the toolbox lid to jump up when the vortex detaches.
This is the same thing that causes those stop signs to violently twist back and forth in hurricane winds.
It is also what makes trees sway in the wind.
You can also see this in fog - but following to close to a vehicle in front of you in foggy is certainly a bad idea.
Joined: Aug 2005
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RE: MPG---- Tailgate down vs Tailgate up
I think my onboard computer missed a memo or a TV show or some-such. My fuel mileage (based on the obc) rises significantly with tailgate down, cruise control on, 64mph........numbers as high as 24.9 (what a stretch of the imagination) The absolute highest reading I get with tailgate up in the same senario is about 18.9........Over the life of the truck, (still pretty new) the overall average fuel economy is stuck at 13.1 and doesnt seem to want to move to much from there. Based on "real wallet" experience, running with the tailgate down yields longer trips and less frequent visits to the pump.
Joined: Oct 2005
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RE: MPG---- Tailgate down vs Tailgate up
ORIGINAL: HankL
If someone from MIT actually tested and found that result with pickup tailgates, please post the link.
Some engineering students from New England College won a ASME (American Society of Mechanical Engineering) prize for this study on a scale model of a 2nd Gen Ram in a water tunnel:
http://web.archive.org/web/200304141...affner/did.htm
Their results are very similar to the Mythbusters results, except that they found that removing the tailgate hurt drag, whereas lowering the tailgate slightly improved the Cd but to such a low extent that it would be hard to detect with anything but the most sensitive of tests.
I thought the Mythbusters episode was 'reasonable' as entertainment,
but running completely out of gas is a poor way to accurately test MPG - although it adds to the drama of a TV show.
When the fuel pump loses prime and starves the engine is pretty variable, and you could not count on one truck dying with exactly the same fuel left in the tank as the other truck. It could easily vary by 1-2 gallons.
Off camera the Mythbusters crew may have checked the two 'matched' Ford trucks over similar 300 mile test runs to see that they were indeed about the same MPG.
The 18 wheel truck industry has been tackling the problem of doing good MPG tests for several decades and in the Society of Automotive Engineers/Truck Maintenance Council Type IV test the standard proceedure is to take two nearly identical trucks and run them as a pair across the highway test run distance AT LEAST THREE TIMES before modifying one of the trucks and doing the real test to see if a mod improves or hurts MPG.
In the SAE/TMC Type IV test they also recommend doing another 'double check' test where you swap the mod onto the other truck that had been un-modified on the previous run.
In the case of the Mythbusters test of the Fords, to really nail down whether the tailgate down helps or hurts they should have done the test again, this time with the truck that had first trip had the tailgate down now traveling with the tailgate up, and the other truck previously with tailgate up now travelling with tailgate down.
But hey, its a TV show on a budget with time deadlines....you can't expect them to do it completely right.
If someone from MIT actually tested and found that result with pickup tailgates, please post the link.
Some engineering students from New England College won a ASME (American Society of Mechanical Engineering) prize for this study on a scale model of a 2nd Gen Ram in a water tunnel:
http://web.archive.org/web/200304141...affner/did.htm
Their results are very similar to the Mythbusters results, except that they found that removing the tailgate hurt drag, whereas lowering the tailgate slightly improved the Cd but to such a low extent that it would be hard to detect with anything but the most sensitive of tests.
I thought the Mythbusters episode was 'reasonable' as entertainment,
but running completely out of gas is a poor way to accurately test MPG - although it adds to the drama of a TV show.
When the fuel pump loses prime and starves the engine is pretty variable, and you could not count on one truck dying with exactly the same fuel left in the tank as the other truck. It could easily vary by 1-2 gallons.
Off camera the Mythbusters crew may have checked the two 'matched' Ford trucks over similar 300 mile test runs to see that they were indeed about the same MPG.
The 18 wheel truck industry has been tackling the problem of doing good MPG tests for several decades and in the Society of Automotive Engineers/Truck Maintenance Council Type IV test the standard proceedure is to take two nearly identical trucks and run them as a pair across the highway test run distance AT LEAST THREE TIMES before modifying one of the trucks and doing the real test to see if a mod improves or hurts MPG.
In the SAE/TMC Type IV test they also recommend doing another 'double check' test where you swap the mod onto the other truck that had been un-modified on the previous run.
In the case of the Mythbusters test of the Fords, to really nail down whether the tailgate down helps or hurts they should have done the test again, this time with the truck that had first trip had the tailgate down now traveling with the tailgate up, and the other truck previously with tailgate up now travelling with tailgate down.
But hey, its a TV show on a budget with time deadlines....you can't expect them to do it completely right.
