It's all about wind resistance. My ScanGauge recently returned 9.5 mpg @ 55, 9.0 mpg @ 60, 8.0 mpg @ 65. This was all into a 15 to 20 mph headwind. So you have to decide what your own "sweet spot" is. It's all a trade-off between speed and mileage. For me that means 60 mph based on my equipment. Wind resistance is geometric. 60 mph is 4 times the wind resistance of 30 mph. So you pay a big penalty as speed builds. On that same weekend, we were able to tow in overdrive and got 12 mpg because of a tailwind.
Other things to consider: 1) Buy a lower profile trailer. We bought a Surveyor partially because edge of roof height was 8.5' versus many others at 10' 2) When you have good conditions (e.g. no wind or tail wind) consider driving a little farther that day 3) Follow a semi traveling your speed or another RV. Just be careful to keep a safe distance for braking and reaction time. It does save fuel. The guy in front of you might not like it though. Use common sense. 4) In hilly areas, dis-engage the cruise. Let your speed creep above your average speed on the way downhill and below it on the way up. It saves "kick downs" and burning extra fuel 5) keep your tire pressures at maximum 6) I swear synthetic oil buys me an extra .5 mpg (not towing, not sure it would be signficant when towing) I've tested it numerous times
Bob, Wendy,& Spanky the Fox Terrier
F150 FX4 5.4L 3.73's
Surveyor 235RKS
Reese Straight Line
Prodigy
I just installed my Scangauge II and was surpised by the change in fuel usage by changes in throttle and speed. I bought the ScangaugeII so I can keep an eye on Trans temp, but it may pay for its self in fuel savings. Havent used it towing yet.
Back in January I installed a new cam and exhaust in my truck. With 4.10 gears and the size of tires I have it runs just under 3000 rpm at 65 mph.
I picked a cam and indexed it for peak performance at 3000 rpm and that's where it seems to perform the best and get the best gas mileage.
I believe the newer vehicles are designed to get their best mileage at lower rpm's, probably closer to 1600-2000 rpm range.
TV: Mint 1972 Ford F-250 XLT
TT: 1969 19' Excel; entertains 6, feeds 4, sleeps 2 You don't shoot to kill, you shoot to stay alive.
I don't carry because I have to, I carry because I get to. My pictures
Read this article in the local paper and thought it was pretty closely related to this thread. Can be found at www.theday.com also. Enjoy!
Life In The Slow Lane
By Kenton Robinson
Published on 6/1/2008 in Home »Features »Features
The blonde in the white Jeep Laredo wants me dead.
She repeatedly drops back, leans on her horn and charges me, stopping just short of ramming my rear end.
Her face is a knot. Her hands - one on the wheel, one clutching a cell phone to her ear - are fists. She's road rage personified.
This, I have learned, is what to expect when you drive the speed limit.
Suddenly, I'm in everyone's way. Suddenly, I can look in my rearview mirror and count the bugs on a semi's grill. Suddenly, with each car that passes me, my life passes before my eyes.
So why on Earth am I doing this?
To save gas.
After all, gasoline, as of this writing, is going for $4.25 a gallon, and, according to the experts, I could save big simply by slowing down.
”Not to speed will save you gasoline, and it can save you a considerable amount,” says Jim MacPherson, spokesman for the Hartford-area AAA.
Indeed, according to the folks at the U.S. Department of Energy, your mileage will decrease dramatically at speeds over 60 mph.
This is mainly, says David Greene, senior research staff member of the Oak Ridge National Laboratory in Tennessee, because of aerodynamic drag.
”Air has mass, and when you want to push it out of the way, you have to accelerate that mass to the speed of your car,” he says. “The faster you're going, the faster you have to accelerate the air to push it out of your way, and that takes more energy.”
So I decide to try an experiment:
1. I will fill my tank and drive it dry the way I always do - speeding like every other bat out of hell on the thoroughfares of this fair state.
2. I will fill it up and drain it again - this time strictly observing the speed limit.
3. I will reap the rewards of my prudence.
The first part of this experiment goes smoothly enough. I cheerfully barrel up and down from Hartford to New London (my daily 100-mile round-trip commute) and everywhere else in between.
And when the tank is dry, I find that my 2001 Volkswagen Jetta's getting 29.7 miles per gallon.
Not bad.
It's the second part of the experiment that turns out to be both revelatory and terrifying.
First off, the speed limit's lower than you ever thought, now that you're paying attention.
For example, on the streets of many cities and towns - in New London, Pawcatuck and Norwich (where I meet the white Jeep Laredo lady) - it's often a mere 25 mph.
Twenty-five miles an hour! Have you ever actually done this? People in wheelchairs will pass you (and curse you as they do).
Secondly, while having a top speed of 65, many of the state's highways have sections where you're supposed to slow down to 55 or even 45. There's a stretch like this on Route 9 going into Middletown, another at the end of Route 2 going into Hartford.
I quickly discover that unswerving obedience to these speed limits is tantamount to suicide, with drivers nearly rear-ending me and then, as they furiously pass, threatening to add injury to insult.
”Keep an eye in your rearview mirror for people who do not appreciate the fact that they've actually come across somebody who's doing the speed limit,” MacPherson suggests.
Which brings me to …
Third, no one, not even your off-duty state trooper, ever obeys the speed limit. Most drivers choose a default speed in the neighborhood of 75 mph.
Fourth, some people, of dubious intelligence, actually drive under the speed limit, meaning that, if you're religiously hewing to it, you must pull out and pass, and God help you if you do.
Meanwhile, I'm doing 25 on streets I used to do 35 on, 35 on streets I used to do 45, and 55 in places where I normally did 75.
My commute, which used to take - depending on traffic - 50 minutes to an hour, took 10 to 15 minutes longer.
But I find there is one big advantage: I set the cruise control and relax, enjoying the slow procession of the scenery, no longer having to watch for speed traps.
When I finally finish phase two of my experiment and calculate my mileage, I find I got 33.4 miles per gallon by going the speed limit. This represents an improvement of 3.7 miles per gallon, a 12.5 percent increase in mileage.
This means I could get 37 more miles out of every 10 gallons. Or, given that I put approximately 35,200 miles on my car a year, I could save - if the price of gas stayed at $4.25 - roughly $556 a year.
As I poke along Route 2 in Norwich at precisely 25 mph, the blonde in the white Jeep Laredo finally snaps. She guns past me on a blind curve, only to meet - head-on - a giant dump truck.
She dodges right, cuts me off and, somehow, we all stay alive.
So the question before us is this: Is my life worth more than $556 a year? Or is the instinct for self-preservation more powerful than the will to save a buck?
”I have jokingly said when I have (seen) really great fuel economy results in a hybrid,” says MacPherson, “that the only good thing about the experience is the people behind me weren't heavily armed.”
1998 Ford Expedition
2008 Flagstaff 27BHSS
Camping nights in 2008: 21
For me, slowing down to 55 mph would mean having to turn off O/D and thus my fuel economy drops by 2 mpg. Keeping it in O/D between 65-70 mph yields the best mileage...and it gets us to the CG quicker, too!
Great story above. And about people not being heavily armed...they really are heavily armed, via their two-ton (or more) vehicles.
Just yesterday, I was lawfully doing 45 in a 45 construction zone in my Jeep Wranger and the large 18-wheeler behind me tried to bluff me faster, which I happily ignored. Finally, in a double-yellow-lined and no-passing-signed zone on a hill, he made his move. I immediately slowed down to let him clear faster and laid on the horn, just as another car coming toward us topped the hill. He almost hit me with the tail of his trailer as he swerved back into the lane. We all lived through this near-disaster, and he quickly disappeared out-of-sight in the 45 zone.
This past weekend I drove between 55 and 58 on interstate highways and got about 1 1/2 to 1 3/4 MPG better millage. It was a lot more enjoyable trip also.
That kind of MPG difference will make a nice difference in the pocket on our upcoming 1400 mile trip. Now we will even be able to eat.
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