So I had to go over to Jacksonvile this past weekend. Going over from the panhandle, I was pulling a 5x6 trailer, empty. Went ~80 mph on the interstate going over, cruise control on, and It took very close to a full tank to make it from FWB to Jax. (Around 350 miles)

So, on my way back to FWB, I had a full load, trailer loaded with my daughter's bedroom furniture, bed and cab loaded with boxes and bags of clothes. I set the cruise at 69 mph, and arrived in FWB with just under 1/4 tank to spare. Same distance both ways, and I filled up just before hitting the road on both trips, just slower driving on the way back.
I always hear things about going slower saves gas, and I admit that I have a heavier foot at times, but I will be going slower from now on because this trip proved it to me that going slower WILL save you gas!
At $3.15 a gallon, I am convinced!

 

Oh yeah, I just did 1500 miles two weeks ago and posted up my findings. When I was going pretty fast (75-80'ish) I was getting about 16-17 mpg. When I'd go 65 and keep the RPM under 2000, I averaged 22 mpg on two different legs of the trip.

 

Cant tell ya where I got it from, and im sure it is a very very generic formula, but .01 mpg lost for every 1mph speed is increased

 

That may be accurate in some aerodynamic sports car between the speeds of 40 and 70, but when you get above 70, and especially above 100, you're REALLY fighting some wind.

.01 mpg at 1 mph would be .1 mpg per 10 mph...and 1 mpg per 100 mph...that's WAY off.

I think the Bugatti gets like 14 mpg at 80mph...when it starts to hit 150+, they were getting somewhere around 4 mpg...so the decrease is a lot more than you give it credit for being. At 210 mph, I believe they said something about 5 minute and they're out of gas...that's pretty bad.

I'd say there's a trade off...Heck at 70 mph, going down a mountain, you STILL have to hold the throttle on to fight the wind...Trust me, our trucks are like huge, rolling bricks as far as the wind is concerned.

 

In most vehicles, especially in trucks and commercial trucks gas mileage decreases exponentially once over 65.

 

Which reminds me:

Went to Vegas (from San Diego) for a track event (in which the motor let go in the 4th lap of the first session, lame ) and got about 12mpg going there convoying with my crazy friends (75-90mph towing, *******s... ). One of my friends was getting 11.8mpg towing a ~10,000 lb 28' toy box that was about 2 feet shorter than an 18 wheeler's trailer with his 2500 Cummins Dodge with a programmer (peaking at 42psi of boost, yikes!) and was pulling away from me up grades.

On the way back, I was towing behind him and no one else was there to egg us on, so we maintained about 65-75mph and I got about 15mpg...

 

Aerodynamic drag increases exponetially vs. speed. When you start with a high Cd vehicle liek a pickup, then add an 8x8' wall behind it (travel trailer), it goes up significantly as speed increases.

Gotta pay to play (the high speed game).

 

It is strange what a few mph will do isn't it. A few years ago I took my parents old truck and camper to the august NASCAR race in michigan. The truck is a 99 F350 4X4 DRW SC 7.3L PSD/6spd with chip/intake/exhaust and the camper is a 02 Jayco Designer series 35' 5th wheel (about 13,500 lbs wet) On the way to the race we were moving pretty good 80-85 mph most the time, we got 7-8mpg (I don't remember exact numbers but I know that some were 7.something and others were 8.something). On the way back we were doing either the speed limit or 5 over and we were getting 12-13mpg.

Another kinda strange thing is that when dad and I would up north fishing and take that truck with the pick-up camper (about 3200lbs) and towing the boat (about 2500 lbs) the truck gets the same mileage as when towing the 5th wheel. Dad has found this to be the same as with his new truck (same as the 99, just an 05 with 6.0/auto). The weight doesn't effect the truck at all even though there is over 6,000 lbs differance between both setups, but they do both have about the same wind resistance.

 

You do know that most 18 wheelers are pulling a 53' trailer, right? Some 48', I've never seen one pull a 30'