Just took a trip in my Truck and did a experiment got 15.6 mpg with tailgate up got 17.6 with tailgate down. with the cruise set @80 mph.

 

Averaged over how many tankfulls? In August I drove to Colorado and back (1900 miles each way) in my '94 Ranger. On the way out I had the tailgate down and averaged 19.5 mpg over the entire trip. I ended up buying a Stihl pole pruner out there and bringing it back with me so I had to close the tailgate to secure it. On the return trip I averaged 21.7 mpg for the 1900 miles. I was driving the same boring interstates at the same speed both ways. Kansas is real boring on I-70 at 80mph for 435 miles.

It is quite easy to have some discrepancies from one tank to the next, especially since we can't see if we are filling the tank to the exact same level (and therefore one of our two figures is inaccurate). This most recent trip was enough proof for me once and for all and I will never again leave my tailgate down with the false supposition that it will increase my fuel efficiency.

 

There have been scientific studies proving that mileage is best in a PU with the tailgate up. If you search on this forum, you'll find a link to one.

 

well then maybe it was the gas.

 

What About A Tonnau Cover? Does That Increase/decrease Mpg? Or No Affect?

 

H63-
tonneau covers are GREAT for fuel economy! Typically 2-3 mpg gains with highway driving. If I didn't need the toolboxes and open bed, I'd have one.

 

This is my philosophy. If the tonneau weight alot, it will decrease the MPG because of the added weight. I just cane see a tonnno making that big of a difference, even if it is a light tonno. But only personal experience will tell the story. I have no personal experience in tonneaus.

 

do a test with the tailgate off

 

Again...not according to the studies. They say 6% or so better mileage with a closed bed. I saw about that when I installed mine. I had about 1500 miles on the truck when mine was installed. I suspect the mileage will get better with time, but it IS a 5500 pound brick....it's never going to get good mileage.

 

Wouldn't going to Colorado be uphill, while coming back to Kansas be going downhill?

Also it seems reasonable that with the tailgate down, you would decrease wind drag.

 

I did alot of driving with my tail gate down when I first got my truck. The only thing I noticed was ZERO increase/decrease in MPG and small scratches andchips out of the pain on my tailgate. If you think it will help with the tailgate down, just take it off.

 

I honestly don’t mean to step on any tails, but I am very sick of the references to the studies that say there is no difference in mileage with the tail gate up or down, or that it’s better to put the tailgate up.

Total junk reporting.
I’ve read four or five of these ‘scientific studies’ on the tailgate up/down controversy.
None of the articles give you ANY of the relevant facts needed to judge the tests adequately.
Wind resistance is NOT a constant. All the proponents of leaving the tailgate up treat the aerodynamics of the truck as a constant. Totally meaningless in the real world, where your speeds vary from 0- max over and over in a day. Even on the freeway, your speeds range from the LA Crawl, to 80+.
The ‘wind pocket’ that causes a ‘slip stream’ over your bed occurs at what speed? No answer is available in any of the articles. You know it doesn’t exist at town speeds. Test it yourself by putting a piece of paper on a string in your bed. Watch it flutter up and out at most speeds. Try to find a speed that doesn’t make it fly out of the back of the bed. In theory there would be a ‘dead area’ just inside the back of the bed at certain speeds. And that may be true. So for the 10 minutes your is at that airspeed, the tailgate helps you. Of course when you drop down for a slow moving truck, then nail it to pass, you invalidate the ‘dead area’. Or when the wind slows down, changes direction etc, there goes your ‘dead area’.

Dropping the tailgate risks damaging it. Some trucks (old 60’s Chevy’s for example,) worked well with the tailgate down. The arms locked, holding the gate straight back and level. But many trucks use cables, so the gate will bounce itself to death if you lower it. No savings there.
Some tonneau covers weigh 75+ pounds. Probably not cost effective. The best bargain for mileage in a tonneau cover would be one of the 75-125 dollar cheap models, but watch for high wind resistance from the area around the fasteners.

In all cases, unless you drive at certain speeds for long periods of time, you may not notice much change. If someone does notice a large change it might very well be that he drives at just the right speeds.
It could be that lowering the tailgate will get worse mileage, IF he drives at the speeds his trucks body develops the ‘dead area’ slipstream.

Every vehicle body will have different ‘dead area’ speeds, and different drag coefficients. Change the angle of the truck, the trim on the cab etc. and the drag will change.
Change the tire size and thus the ground clearance and drag changes again.

By the way, the studies that I have seen on both sides of this issue are VERY suspect.

Tonneau makers want you to believe you will get much better mileage with their product.

Toolbox, camper, and bed liner makers want to discourage you from getting tonneaus, so they will tell you it makes no difference.

Oddly enough, they are both right.
Sorry for the rant, but how many times can this be rehashed without any new data?
Chris

 

I tried four weeks of driving with the tail gate up and then four weeks with the tail gate down and no difference in fuel mileage. I drive on average 750 kms per week. I no longer worry about dropping the tail gate.

 

There is a company that makes an automatic tailgate opener that will open the tailgate at the push of a button and it also will open it a little with speed so that it acts like a spoiler. Of course there is a setting that makes it stay shut incase you have cargo. Also acts as a locking feature, but I would guess it woul be a pain in the butt if your battery were dead.

 

My personal experience it that what is gained in fuel economy is consumed by additional weight. $900.00 experiment failed, but looks good in doing so.