Speed vs. MPG in Real World

I've taken some fairly long trips and have travelled at different speeds, to compare the effect of speed on fuel economy. I suspect some here may be interested.

All tests were done with a Chevy diesel pickup.

1. No trailer, 80MPH "indicated" (Officer, I'm sure I go much slower than that, I'm sure the speedometer is off...): about 15 MPG

2. Towing 2619 at 70 MPH: about 17 MPG

3. Towing 2619 at 60 MPH: about 20-21 MPG

I haven't tried long distances at 60 or 70 MPH without the trailer, and there's no way I'd tow at 80 MPH, so I don't know what the TM is doing to MPG, but I suspect it's very little. Much more significant is how fast I'm driving the thing. It's nice to have such a fuel efficient trailer (when I tell other Chevy diesel & RV owners that I can get 20+ MPG while *towing* they are shocked - I've heard plenty of things like, "I really like the diesel because I get almost 10 MPG when towing!").

All tests were at about 5000 feet above sea level, about 65-75 degree temperatures.

Some other calculations... Assuming diesel costs about $3/gallon, and a 2000 mile trip with my truck:

At 80 MPH (no trailer): $400 of fuel

At 70 MPH (with trailer): $352 of fuel

At 60 MPH (with trailer): $300 of fuel

Of course it'll take about 25% longer to get there at 60 MPH, assuming no stops - but who doesn't make stops? You're also filling up at least one less time at 60 MPH, which probably eliminates some delay. If you want to get there fast, do what a truck driver friend of mine (who's an independent operator - so he drives 60 MPH in his truck, he likes to make money) says: "To get there quick, you just have to make sure you don't use one control: the left door handle."

That all said, I'm definitely in favor of people stopping when they need to and generally taking it easier. You'll still get there, you'll see more, and you'll be more relaxed. Oh, and save a bunch of money (including money on things like maintenance of the vehicle and tires).