I just did the same road trip with my RollBak tonneau cover installed and cruise locked in at 73 mph and averaged 17.6 mpg.

 

It is proven science that there is a natural vortex created in a truck bed that once up to speed the air naturally flows over the vortex, thus not creating drag. You've seen a piece of trash or paper that looks as though it is just floating (hovering) around in the bed of a truck while it's driving at a good speed.....and then it finally drifts out of the vortex and flies out into traffic. This proves that trucks are engineered to be driven with the tailgate up and it defeats the purpose to have the tailgate down. My brother has a soft lid on his Siverado 1500 and he said that he notices the middle of the tanneau beats up and down considerably while driving on the highway...this is the vortex that is trying to establish itself but cannot bc of the cover. I'm not saying that hard lids are not efficient, but trucks are designed the way they are for a reason.

 

I also love the people that leave their tailgates down when they park their trucks to go inside a hardware store or something. I don't think they realize that two people can remove a tailgate without tools in under a minute without setting off the alarm...

A neighbor down the street had his parked outside his house, the tailgate was up but unlocked and it got stolen, never to be seen again.

 

True, I laugh when I see people riding with the tailgate, Plus if you get in an accident with the Tailgate down it will screw up your truck even worse!



02 F-150 Screw, 4.6L, K&N FIPK, FlowMaster 40 Series S/I D/O troyer Superchips Custom Tuning 5-program 4-bank Performance Chip! Dark Shadow grey, Access Lite Rider Low Profile Tonneau Cover

 

True! I've also found out personally that having the receiver w/ ball on a Jeep Grand Cherokee (wife's ride ) and being hit from the rear at almost a dead stop by a Ford Focus traveling approx. 50 mph will bend the HELL out of the frame. It will push the draw tight system up under the rear of the vehicle and actually crease the roof of the Jeep dead center like a pair of starched wrangler jeans This actually happened and the dang body shop actually straightened it back out and fixed it. Keep in mind that the receiver actually tore the Hell out of the Focus and was somewhere near the in dash radio when the wrecker pulled them apart , but I still think that it didn't help our Jeep either. I leave my receiver out of my SCREW and Jeep unless I know I am going to tow something.

 

An interesting video and info on this subject here: http://www.youtube.com/watch?v=ncHDICujq88

 

Yes, the bed is designed the way they are for a reason = to haul stuff.

The vortex in a bed and how it affects drag has many factors that don't ALWAYS add up to the same results.
1. Individual design of cab.
2. Length of cab.
3. Design of bed.
4. Length of bed.
5. Individual drivers cruising speed.
6. Toolbox in bed?
7. etc...

 

In addition to drag... what would be interesting here would be the measure of rear 'down force' with the partially open tailgate.

 

Structurally, the truck is much better off with the tailgate up. If God forbid, someone hits your really nice truck from the side while the tailgate is down, I guarantee they will do more damage to the truck than if the tailgate were up. So for me, I'll dismiss the whole idea of this gas mileage thing and leave the tailgate up. Unless of course I have my dirt bike in the back with my bed extender out over the tailgate.

 

Just because the streamers are going down does not mean its bad does it? There is a rolling effect and pressurized air in the bed that keeps speeding air arching over the roof and just beyond the tailgate. Some wash goes into the bed and keeps air pressure up to make in effect a sort of fastback camper in the bed. That air pressure keep the air washing over the cab and down just beyond the tailgate.

I wouldl iek to see a video run with a bike rack in the receiver and maybe a BBQ grill with streaming markers/strings and watch the wash beyond the tailgate, not in the bed itself. Wouldn't your frame of reference to watch be the aerodynamics of the entire vehicle, not the pressures and turbulances in the bed?

Just for sake of argument...

 

There was smoke from a small forest fire over the road and when I looked over at his pick up the smoke was rolling over his cab and smacking right into his tailgate. Then the smoke seemed to roll on itself to get out of the bed of the truck over the tailgate. The rolling effect of the air against the tailgate acts less like a sail and more of an airfoil. In the up position the airfoil shape helps fill the void; however, in the down position the air flow dynamics are changed and this causes a disruption in the air flow dynamics. Ever wonder why the outside of your tailgate has a slightly rounded appearence? By extending the truck bed down you extend the length of the bed. The vacuum created by the cab pushing air out of it's way needs to be filled with air. This filling air has a natural tendency to come from the place of least resistance which would be the back and from under the truck and not the sides. The air from the sides is meeting little resistance and his happy to keep going along it's merry way until it hits the vacuum created at the back of the truck. Also, the side air is under less pressure because it's hauling *** along the sides. The momentum of the side air is headed back and away and to reverse it requires more energy. The air coming up from under the bed of the truck is slightly compressed because it has been pushed against the ground underneath the truck and when it comes out it has more of a tendency to fill the void because it's under slight pressure. By extending the bed the air under pressure has to travel longer and therefore the void must be filled by the side air which has more momentum going away from the rear. The air from the sides is not enough to fill the void in the bed so it has to come from somewhere and that would be from the tailgate area. The airfoil shape of the tailgate also creates more drag when in the down position. With the tailgate down there is more distance the air has to travel to fill the void created by the cab created vacuum. More distance traveled requires more energy and therfore more gas. The rolling effect of the air with the tailgate up helps fill the vacuum created. By having a mesh gate the distance is not changed the air has to travel to get back into the truck bed. The rolling vortex created by the standard truck tailgate does have a trade off but extending the bed of the truck just increases the distance the air has to travel to fill the bed and again, requires more energy.

Lablover

 

I've also heard that if you hit a bump just right, your open tailgate can come right out of the hinges. I just sits there anyway. You can remove it by holding it at about 45 degrees and pulling up & out along the 45 degree line. If it happens while driving it will be drug down the street by the cables & beat the heck out of the truck.

 

I tried a test with tail gate up and down several years ago.

I was making a trip to Philadelphia, Penna. Ran one tank with gate down and one with gate closed. Didn't make ANY difference.

I talked to a Ford engineer and he told me that the only way the tailgate effects fuel mileage is my the total weight of the tailgate. So if you remove it, the truck is "suppose" to get better mileage, since the weight is not on the truck. Shhhhhhh....can't be that much..

 

How did the tailgate hit the bumper? Did he also remove the cables?

 

The odds of that happening are about the same as winning the lottery. The tailgate pivot is under tension.

And it's impossible for those of us whom have done the hose clamp mod to prevent casual theft of the gate.