The point being this.
Even a small increase in speed can use an amount of fuel larger than you would think for going 5mph faster.
Towing my car hauler at 70mph vs a slower 60mph is going to cost me. The power required from 40mph to 80 mph is going to be about 8 times as much. If you could figure out how much power your rig used towing the trailer at 40mph then you could make up a neat fuel economy graph.
But that could be pretty scary.

 

. There is no drag in space, so power is only needed to keep accelerating mass... no power is needed to maintain a speed...


. I see what is confusing you, to go 60 MPH, you don't need to "overcome drag" and go faster, you merely need to equal the drag to maintain 60 MPH... as that chart shows...

 

Your "theory" will only work in a vacuum.
If a sprinter is pounding out 250 watts at 20mph during his lead out, he is going to have to produce over 2000 watts at 40mph during the sprint to the finish. At the highest levels of racing this is an undisputed fact of science.
Maybe you should take up coaching? The Olympic team will only need to generate half as much power.
But I can see what is confusing you. You need to read about power requirements and aerodynamics. Static work requirements are what you are used to calculating.

 

This is why you are confused.
We live in atmosphere. It takes 8 times as much power to double the speed of any airframe.

http://www.wired.com/2012/10/can-we-...-says-physics/

 

You guys are awesome.

I agree with both of you. Going faster takes more fuel.

 

Here is another example of how much drag affects fuel mileage. Towing my 7-8k lb travel trailer which is not very heavy, but is like pulling a parachute through the air, I average from 6.5 to 8.5 mpg. Last week I hauled some hay with my Ecoboost. My 24 ft gooseneck flatbed weighs 4k empty, so I was towing light going one way. Coming back with 10 4x5 rolls I was a little over 10k, but I had very little extra drag. Here was mileage for two round trips.

 

Towing over 8,000 lbs. and my trailer at 34 feet long, I get 8-9 mpg. I think that's normal. My old 2010 with a 5.4 pulled similar weight with my last trailer and got around 7 mpg, and didn't have near the power of my little 3.5 Eco. The Ecoboost engines also seem to have to break in for a long time to get better fuel economy, IMO.

 

My two camping friends both have 3.5 EB 2015 crew cabs. One is decked out the other one is very basic. Their TT's are roughly $5.5-6k when loaded. The basic F150 runs 87 octane as he is too cheap. The decked out F150 runs high octane for 2-3 tanks before each trip & while pulling. My TT is about 1k heavier due to more slides & power everything. I have a F250 6.0 that when in race tune puts down around 800wtq. So its no slouch. My tow tune is roughly 600wtq.
The basic truck on a 3,000m trip this past summer got 8.2mpg, the decked out F150 running high octane got 12.3 & I got 12.7mpg. The EB pulls great but if I am leading (this is extreemly rare as I always bring up the tail in the group due to preferring to cruise around 75mph when leading) their mpg drops like a brick in water and mine only drops slightly. I think the EB's are great! Both had older F150's with 5.4's that got 6-8mpg. FYI my truck dry weighs 8400 for a comparison.
The basic truck's daily mpg is roughly 23 as he drives like a 70 year old (only 46 though) & the decked out trucks avg is roughly 16. As I mentioned earlier the decked out truck runs 87 when not pulling. I average about the same 16-17mpg. More if I could fix the right pedal's issues. 10% or 100% and no in between.

Cheers!

 

I know this is an old thread....

I am dissatisfied with the mileage on my eco also. I tow a 6,000# TT and I usually end up getting an mpg in the sixes. I know the wind affects it greatly, as I commonly drive on an east/west highway known for its wind. Some times I can feel it fighting me. I have tried premium when towing, but not for the few tanks previous. I also heard that turning off the anti-sway when towing is supposed to help. I'll try that next too. I do drive 70 mph usually when towing on the freeway, but it didn't seem to matter any for mpg from 60 to 70, so I figure I might as well get there quicker.

We are looking for a new TT. I wanted something in the 5k weight range, but all the units we like are 6k to 6.5K. Go figure. None of the newer units seem to be made low profile. A unit before our current was a grand surveyor, it had a low profile frame, and towing with our previous 6.0 GM w/4 sped auto tow rig we got 10.0 to 10.5 pulling it. When we switched to the new camper the mileage dropped int the sixes. I thought the eco with the six speed trans would net better economy. Maybe it's our trailer that's the issue. It has a rounded front like the others trailers that posted here, who claim the get 8 or 9 mpg. I almost never get out of 5th gear towing, when I do it's in 4th! Rarely ever get it up into 6th gear while towing.

I sort of agree that the eco is more hype than reality. It's never failed on power, but unloaded I get around 18 mostly in summer and 16 in winter. I have a '13 eco screw w/ 3.55 XLT. I think ram is on the right track with a small displacement diesel that gets 26 mpg unloaded.