Myth Busters

[Scotty]

Mabey you have heard of this. On the show two pickups, one with the tail gait down and one up. the one with the tailgait down ran out of gas First. The tailgait up drove 30 miles further. Seems drag will occur with the tailgait down. Interesting.


Scotty

 

[1848]

I think you will get that variation in any two vehs compared to one another. Moving 4 or 5,000 lbs down the road without a tailgate down?....cmon. What's the difference. Same thing as A/C on vs windows down...it's irrelevant!

 

[DiamondSCattleCo]

Every new body-style Ford and Dodge pickup truck since 1994 has been like this. The end gate down, or missing will increase aerodynamic drag on the vehicle, hurting your fuel economy. A southern University (doggoned if I can remeber the name) did a wind tunnel test on a 2nd Gen RAM pickup truck (2001 I think) and they found significant disturbance with the end gate down or removed.

I'm a member of a Dodge RAM truck mailing list, and there is a guy on there who is constantly doing mpg experiments. He went through 10 tanks of gas, 5 with end gate, 5 without, and with his truck (1998 360), he got .5 mpg better with the end gate on.

Rod

 

[1848]

I'm sure all that driving was averaged for same road conditions, veh speed, wind speed/direction etc. too..right? :roll: If I concentrate hard enough I'm sure I could increase the gas mileage on my push mower... :lol: :lol: I don't think it is worth the trouble...but I'm sure someone can figure up the fuel cost at .5 miles a gallon and put a figure to it. Meanwhile I'll focus on leaving my tailgate up and my stuff in the truck...besides I don't think the cattle trailer will benefit from the tailgate down, and if I'm in my truck it's usually behind me..otherwise I drive the 30 mpg car ;-)

 

[DiamondSCattleCo]

I'm sure all that driving was averaged for same road conditions, veh speed, wind speed/direction etc. too..right? :roll:

Thats why he did the experiment over 10 tanks of fuel, to ensure he had a good sample of conditions :roll:

Rod

 

[Scotty]

I'm sure all that driving was averaged for same road conditions, veh speed, wind speed/direction etc. too..right? :roll: If I concentrate hard enough I'm sure I could increase the gas mileage on my push mower... :lol: :lol: I don't think it is worth the trouble...but I'm sure someone can figure up the fuel cost at .5 miles a gallon and put a figure to it. Meanwhile I'll focus on leaving my tailgate up and my stuff in the truck...besides I don't think the cattle trailer will benefit from the tailgate down, and if I'm in my truck it's usually behind me..otherwise I drive the 30 mpg car ;-)

Hence why I said interesting. I hear Dodge has some difference out of the factory on their diesels. Somethign to do with the way the fuel pump is set out of the factory. Too high and fuel gos by unburnt.


Scotty

 

[DiamondSCattleCo]

On the older diesels with the mechanical injection pump, you'd see some variation from truck to truck, but since the switch to the VP44 and CP3 common rail pump, that are all calibrated on the fly from the ECM, most of the variation you'll see can be attributed to fuel differences from region to region and the drivers right foot.

Rod

 

[1848]

I'm sure all that driving was averaged for same road conditions, veh speed, wind speed/direction etc. too..right? :roll:

Thats why he did the experiment over 10 tanks of fuel, to ensure he had a good sample of conditions :roll:

Rod

Exactly! Maybe the 10 with the gate down were more ideal weather conditions with more freeway driving, and less time at stop lights, or fast foods, or run in with the veh running errands. :shock: I don't buy a veh based on a 1/2 mpg better expected fuel mileage, and I don't think most people are going to focus on that either. If I'm driving around town from 25 to 35 mph, keeping my tailgate down is useless. Most new vehs will increase in MPG as they are broke in anyway, so new vehs are out of the test. As far as the guy with the '98 who is always testing... :roll: ....I hope he is getting paid for his effort! .

 

[Campground Cattle]

I'm sure all that driving was averaged for same road conditions, veh speed, wind speed/direction etc. too..right? :roll:

Thats why he did the experiment over 10 tanks of fuel, to ensure he had a good sample of conditions :roll:

Rod

Exactly! Maybe the 10 with the gate down were more ideal weather conditions with more freeway driving, and less time at stop lights, or fast foods, or run in with the veh running errands. :shock: I don't buy a veh based on a 1/2 mpg better expected fuel mileage, and I don't think most people are going to focus on that either. If I'm driving around town from 25 to 35 mph, keeping my tailgate down is useless. Most new vehs will increase in MPG as they are broke in anyway, so new vehs are out of the test. As far as the guy with the '98 who is always testing... :roll: ....I hope he is getting paid for his effort! .

Right on 1848 driving conditions are constantly changing not the laws of physics

 

[DiamondSCattleCo]

1) Exactly! Maybe the 10 with the gate down were more ideal weather conditions with more freeway driving,

2) As far as the guy with the '98 who is always testing... :roll: ....I hope he is getting paid for his effort! .

1) You misread my post. Tailgate down = worse mileage. Dodge reps say it. Ford reps say it. The University study I read said it. And 10 tanks of fuel = ~ 2500 miles. Thats a fairly large cross section, with Hank alternating end gate up and down between tanks. About the only way he could have gotten more accuracy is to have done 20 or 30 tanks of fuel. In other words, driving conditions would have been equalized, fast food stops or no fast food stops.

2) Why roll your eyes? Hank is a retired engineer who has plenty of time on his hands. He gets his rocks off goofing around with trucks and trying to get the best mileage he can. Some people fish, some hunt, Hank plays with tires and end gates and spark plugs.

Rod

 

[1848]

1) You misread my post. Tailgate down = worse mileage. Dodge reps say it. Ford reps say it. The University study I read said it.

It don't change my answer either way

2) Hank is a retired engineer who has plenty of time on his hands. He gets his rocks off goofing around with trucks and trying to get the best mileage he can.

Good for Hank getting "something" out of it. Like I said..I hope he gets paid for it.

To each his own

 

[Scotty]

At the end of the program they talked about finding data from were NASA proved the same thing. Tailgate down is worse than tailgate up. 1848 are you one of those " I will argue with a fence post if I thought I could win" or do I have it wrong.


Scotty

 

[1848]

At the end of the program they talked about finding data from were NASA proved the same thing. Tailgate down is worse than tailgate up. 1848 are you one of those " I will argue with a fence post if I thought I could win" or do I have it wrong.
Scotty

NASA...wow! Now I feel like this has gone way too far... :shock:

:lol: :lol: Sometimes it is just me and the post out there Scotty, so I have gotten good at it!

P.S. In case you wondered why the tailgate up/ down is better..?

Try following a big truck on the highway sometime...it's not scientific... it has to do with the push created by turbulance behind the truck. Nuff said

 

[Scotty]

Just have to stir the pot sometimes. most of what you stated i agreed with. As for me. I have no tailgate. Really, it got stolen in Dallas.


Scotty

 

[1848]

:lol: :lol: :lol:..... ;-)

 

[DiamondSCattleCo]

P.S. In case you wondered why the tailgate up/ down is better..?

Try following a big truck on the highway sometime...it's not scientific... it has to do with the push created by turbulance behind the truck. Nuff said

<chuckle> You're absolutely right, thats not scientific at all.

There is no "push" created by turbulence, quite the opposite in fact. When a truck trailer (or any vehicle for that matter) moves through the air, it generates a vortex behind the trailer. If you follow a highway tractor unit, your vehicle will get caught in this vortex, pulling your vehicle along. Its the same concept Nascar drivers use when drafting.

This same vortex that pulls you along is also pulling against the vehicle thats creating the vortex. You ever bother to look at those "bumps" on the top lips of new endgates? They're there for a reason: To smooth airflow as it goes over the backside of the truck, reducing the vortex effect and the drag on the truck. Thats also why you're starting to see more and more truck trailers equipped with those little aerofoils pasted onto the trailing edges.

Rod

 

[Bama]

Hey while were talking about the laws of physics ponder this.

Very few things are pulled most everthing is pushed. Yep, we actually push a cattle trailer. Think about it.

 

[J]

All I can add to this is the fact that the bed of my truck is never empty enough to run safely with the tailgate down. I would venture to guess that most on this board have the same problem. If you use your truck to work out of the bed is a work area. Probably doesn't save enough on fuel for me to clean it out anyways. ;-)

 

[dcara]

I can't remimber where I read it but about 5 years ago I read an article about some wind tunnel tests that some group did with the tail gate up and with it down. Bottom line is that there was less aerodynamic drag with the tailgate up due to what they called the bubble effect. With the tail gate up a pressure bubble was able to form in the bed of the truck which acted to support a smooth and laminar airstream as it flowed past the cab and over the tailgate. With the tail gate down the pressure bubble was very weak and and allowed eddies and horizontal vorticies to develop as the air stream flowed past the cab. As anyone that understands aero and hydro dynamics will tell you, vorticies are known to be the demons of drag. In short, keep the tail gate up to reduce vortice induced drag.

 

[dcara]

Almost forgot. Regarding the push pull issue. Whether you are pushing or pulling is determined by where the center of gravity of the load is relative to the impilsion force with regard to the direction of travel. If the impulsion force is ahead of the load in the direction of travel then you are pulling. Hence we normally PULL trailers forward since the impulsion force on the hitch is ahead of the trailer in the direction of travel; and we PUSH them backwards since the impulsion force is behind the load in the direction of travel. Pushing and Pulling have the exact same energy conversion effiecny but pulling is always a more stable configuration.