Aerodynamics engineers have found that wind resistance is actually lower when the tailgate is up. Why? When the tailgate is raised, a "separated bubble" of stagnant air is formed in the bed of the pickup. Wind tends to swoosh over this bubble as though it were part of the truck. Lower the tailgate, and the bubble disappears, which leads to increased wind resistance.
HobbyTalk beat me to the explanation. With the gate up, a stagnant "bubble" of air is formed behind the cab because it can't flow out the back of the bed. The resistance of air flowing over the truck caused by the forward movement of the truck hitting a stagnant pocket of air is less than the resistance of air flowing against the surface of the bed of the truck. The resistance is a function of the velocity to the second power, so the difference will become greater as the average speed goes up.
Now if the tailgate was taller than the cab, 1) your mileage would indeed go down with this tailgate installed, and 2) you would have a really weird-looking truck. But that is essentially what a fiver is - a tall tailgate - that weighs 12,000 pounds.
Steve in East Tennessee
2008 Jayco Eagle 299 RLS
2008 Silverado 2500 4x4 Crew Cab SB
Duramax LMM Diesel/Allison Transmission
I have a Custom Flow steel 5er/GN tail gate. I sprayed it color matced to my truck. I've had many different trucks over the years and pulling a GN or just the 5er makes it handy.
As others have pointed out air turbulance in the bed is a problem with a stock tailgate with a 5er. Zero problems with the GN trailers.
I had over 600 mile a week commute for over 30 years. I've ran diesels/big blocks/smallblocks and even the old inline sixes in the older trucks on that long hiway commute. No difference in mpgs on any of the trucks loaded or empty with V gate or stock gate or no gate.
I have noticed my current truck in sig handles/tracks better when not towing in strong sidewinds with the stock gate on vs the flow through.
You can't beat having a V gate when you use a trailer as much as I do. Even the RV.
"good judgment comes from experience, and a lot of that comes from bad judgment" Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach Linex
'97 Park Avanue 28' 5er with two slides 16" BFG Commercial LTs
HobbyTalk wrote: Aerodynamics engineers have found that wind resistance is actually lower when the tailgate is up. Why? When the tailgate is raised, a "separated bubble" of stagnant air is formed in the bed of the pickup. Wind tends to swoosh over this bubble as though it were part of the truck. Lower the tailgate, and the bubble disappears, which leads to increased wind resistance.
Not trying to argue your point, just want to understand your point. Are you saying this bubble happens both bobtailing and hauling? I ask because I have seen items fly out of my bed ( accident) and I assume it is the wind. If you were to put a 4x4x half inch sheet of plywood in your bed I would think it would fly out very quickly without a gate, no resistance. With the OEM gate it would also fly out at some point. Why would it with this bubble in place? Just a thought.
06 Dodge 3500 QC LB Laramie 4x4 Dually 5.9 Cummins Auto Jacobs brake Dodge Nav
GVWR 12,200 GCWR 23,000 payload 4830
06 Grand Junction 34' High profile 15500 GVWR 3300 pin weight Mor/ryde pinbox 7k axles
5500 Onan genny, Dual A/C, Fireplace
Total 21500 GVW
I think that the "bubble" concept only applies when running empty. I know for a fact that with the OEM gate under my 5er there is extreme turbulence that is not there with the notched gage.
Keith
Keith, Gloria & Charlie(Spoiled Rotten Boston Terrier)
2005 Ford F350 CC DRW 4X4 PSD Auto
2007 Everest 295TS
2008 Honda Goldwing
USAF 1968-1976 Viet Nam Veteran
Jetboat I would buy that gate, I think it is a great deal. Just paid way more for my transfer flow. I also made a center panel to fill the notch when not towing. Helps keep the honest people honest. I can also lock my gate and with the cover on no one can see what is in the box of my truck.
Hotel California wrote: I had a slight mishap and got a V-gate.
A year or so later, was camped in a space with uneven ground. Thought I had enough clearance to back the truck onto the pin, but guess what? Yep, hit the center of the V with the pin. Dent is still there 4 years later to serve as a reminder that there is no limit to my stupidity.
Thank you for posting. I thought I was the only one who had ever done that! Same situation, uneven ground. Kept mine for three more years until a guy at Sears put too much weight on the gate when loading something for me. Good excuse for getting a new one.
Dave
'08 Hitchhiker Champagne 35LKRSB
'08 Ford F450 6.4PSD
rick83864 wrote: Not trying to argue your point, just want to understand your point. Are you saying this bubble happens both bobtailing and hauling? I ask because I have seen items fly out of my bed ( accident) and I assume it is the wind. If you were to put a 4x4x half inch sheet of plywood in your bed I would think it would fly out very quickly without a gate, no resistance. With the OEM gate it would also fly out at some point. Why would it with this bubble in place? Just a thought.
I work with a fluid dynamicist (yes, they really exist) and he was showing me some simulations of air flowing over the cab of a truck with and without the tailgate. This is without hauling, and the bed empty. For the case with the tailgate up, the air initialy hits the gate, goes down and moves along the bottom toward the front of the bed, where it creates "vorticies" that shed off the top of the cab. Without the gate, the air gets sucked down directly onto the bed, and many more vorticies shed from the floor of the bed. That's why there is less resistance with the tailgate up.
Now when you are towing, the target area for the air to hit pretty much doubles. Air hitting the front cap of the fiver flows off the sides somewhat, but most either goes up and over or straight down. The air that goes down would hit the tailgate forcefully, because it has nowhere else to go. That is what is creating the turbulence. When there is no taligate or a notched gate with louvers, the air can exhaust out the back and hits the first vertical wall of the trailer or flows right under the trailer. Interestingly, this causes a slight lift on the trailer; whereas the air flowing under the truck creates a slight vacuum.
I know there are some animated simulations of the non-towing case out on the web somewhere. I'll look for them and post links. It is very counter-intuitive, but you can see air flows much more smoothly when the gate is up versus when it is down.
Then there is the third case with the tonneau cover. It is best-case, as air flows smoothly off of the cover without having to make such a big turn to fill the vacuum left by the empty bed. The flow path looks more like a car than a pickup truck.
I am neither an Aerodynamics Engineer nor a Fluid Dynamicist.
However - I can vouch for the dynamics of a stock tailgate aerodynamically "flowing" from the back of your pick-up into another vehicle.
Several YEARS (maybe the life of the truck) of any mpg advantage - if there is any - will evaporate when you pay the deductible on your insurance, or elect to purchase a stock tailgate outright to replace the stolen one.
It is *BIG* business!
How big? Twenty tailgates went out/off of pickups in a L.A. Times,
security-guarded parking lot in one "event".
There is *NO* market for stolen "V" gates - but LOTS more folks (than FWers) back into "things" (or vice-versa) on the farm and in the city, and need a replacement for their "stocker".
Of course, if your tailgate is *stolen* - - - you need one also.
Viscous cycle!
~
And, of course "cwit(s)" point is well made - if you save a theft of "whatever" from the bed of your truck, because it's out of sight -
you just received another "dynamic" benefit, LOL!
~
* This post was
edited 11/15/09 12:14pm by ol Bombero-JC *
Might get one eventually, but they aren't strictly neccessary. Mostly take your time and go slow when hooking and unhooking.
With an 8' bed, we can hook up from any angle with the tailgate down.
I leave several chunks of 2x6 in the bed (from 1 to 4 foot long) and have never seen anything suggesting they might fly away. Could this be an issue with higher speeds (I rarely exceed 60mph)?
Now to my idea:
I've seen flexible screens for MH's that run from the lower back of the MH to the lower front of the toad primarily to keep stones from hitting the toad. What if the attachments were taken from the upper rear of the cab to the upper front of the 5er? This would create an wedge to smoothly transition air flow from the top of the cab to the top of the 5er. I suspect this would provide much better results than a wing that stops several feet from the front of the 5er. Any thoughts?
Tammy Mike & the Bilge Rat (AKA: Diego)
Ford F250 7.3L
1997 Sunnybrook 27' 5er
1995 Gemini Sail Catamaran 34'
Full Time spliting time between boat and 5er
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