Is My Speed Off Fuel Economy?

[arcaguy]

Originally Posted by Mr Ted

If everybody is passing you then you are obstructing the flow of traffic and are "That Guy" and should not be worrying about a few gallons of fuel.

Mr. Ted, I invite you to perform an experiment. Get on the interstate highway and set your cruise control at 70 mph or whatever the speed limit is. I will pretty much guarantee you that you will likely be the slowest vehicle on the road, including trucks. I drive 65 mph most of the time and nearly everyone on the road passes me. My point being that driving legally is very, very uncommon. Want another example? The correct following distance on the highway following the old 2 second rule is 205.3333 feet. he current recommendation is 3 second or 308 feet. Most people on the road follow at a much closer interval, generally some small fraction of that distance. My point is that just because many or most people do something doesn't make it legal or safe, it just makes it common.

[Wtbuck12]

Originally Posted by Crasher

The most important speed to drive is the one you are comfortable with. The speed that you feel you are in control for any event. Do not under any circumstances drive at a speed others want to to drive. You are the one responsible for your safety. Driving 60, as long as the transmission is in 6th gear, will get you better fuel economy that driving 65 or 70. If driving 60 on the interstate upsets some drivers, it's their problem, not yours. As long as there is a second or third open lane for others to pass you, you are not "That Guy", they are "Those Guys". Be safe and enjoy your RV.

Agree 110%. I drive what I feel comfortable at and everyone is free to follow or pass, which ever they prefer. I am not in a hurry to get anywhere or to die. JMHO

[twogypsies]

It's not how fast you can drive but how safe you can stop! How well you can control in case of a blow out.

[Mr.Mark]

I started a 1,750 mile trip today..... I checked my RPM's because I couldn't remember when I posted earlier.

At 55, I'm running 1,200 RPM's
At 60, 1,300 RPM's
At 65, 1,400 RPM's
At 70, 1,500 RPM's.

Mark

[Rob_M]

Originally Posted by Mr.Mark

I started a 1,750 mile trip today..... I checked my RPM's because I couldn't remember when I posted earlier.

At 55, I'm running 1,200 RPM's
At 60, 1,300 RPM's
At 65, 1,400 RPM's
At 70, 1,500 RPM's.

Mark

Your Prevost is probably geared little higher than a lot of our RVs. A good friend of mine used to drive a truck for the NASCAR teams and he said the Prevost’s and similar coaches would run over 100 mph easy and they sometimes did.

My American Tradition DP is right at 2000 rpm at 80, and 1800-2000 seems to be the sweet spot.

Running back roads at 65mph between Del Rio and San Antonio, I geared down from 6th to 5th for a while and it got the same or maybe 1 mph better and didn’t shift up and down constantly.
It has a Banks power pack which may affect the torque curve different than a stock 350 hp 8.3.

[Mr.Mark]

Rob, I couldn't believe that Arkansas has changed their speed limit from 65 to 75, truck speed posted at 70.

My personal speed limit is 65 mph. I'll run a little higher to pass but 65 is comfortable to me. I couldn't imagine running 100 mph... I'm sure it could because 70 is smooth as silk!

Safe travels,
Mark

[96 Wideglide]

Our toad is rated to be flat towed up to 65mph, so that is my limit.

[n2zon]

I'm still playing with it, but 62-63 MPH, or the posted speed limit, whichever is lower, seems to be the sweet spot for us while balancing all the factors we care about (time, cost, traffic speed differentials, and so on) most of the time. When we can, 55 is the real sweet spot, just slightly over the engine's torque peak.

From a safety standpoint, you want to stay reasonably close to the 80th (or is it 85th?) percentile speed. Too fast, and you're outside the window of reasonable expectation, and the same is true of too slow. I speed up when traffic is passing by at warp speed, but otherwise slower is better, to a point.

There are often comments here along the lines of, "If you're worried about mileage, you shouldn't have bought one." I'll note, though, that the habits of reasonable thrift are what got us here in the first place. Just because we can afford to buy what we have does not meant we want to buy a lot more fuel to drive it at or above the speed limit. Just a different viewpoint. Hey, the German Swabians think Scots are spendthrifts! We're not quite in a class with either, but neither of us likes unnecessary waste.

[Solo_RV_Guy]

Originally Posted by wolfe10

For a fact-based look at what affects MPG as well as speed expectations on grades:


https://www.prevostcommunity.com/PDF...%20economy.pdf

Brett, that's a great resource from Caterpillar. Thanks for the link!

[PandS]

Originally Posted by 96 Wideglide

Our toad is rated to be flat towed up to 65mph, so that is my limit.

Same for us. I set the cruise control to 63 and maintain that speed, as much as possible, while on the interstates.

Came down route 98 through central Florida today at 55 mph. Tach read about 1550. got almost 10 mpg while enjoying the scenery. Priceless, in my opinion.

We're mostly interested in smiles per mile more than miles per gallon, but we're retired and have the luxury of enjoying the journey at least as much as the destination. -Paul

[Lv2Roam2]

We're just over 60K miles and our 'sweet spot' is ~ 63 mph (1675 rpm) with a Cummins 450. The Freightliner course recommends this RPM / speed combo. While in the 'flatlands' of Florida we average ~ 8.7; elsewhere ~ 8.2. In flat country or gently rolling hills we use the 'mode' button.

Our GCW is 45,500 and we generally travel with full FW / greater than a 1/2 tank of fuel and light waste tanks.

[Mr.Mark]

I have to admit, I secretly love 55 mph. My toad also is rated at 65 mph.

When I'm in California and drive the posted 55 mph 'towing' speed, I'm happy. I can get 7.0 mpg. I know, I know, we spend a fortune on these coaches and I think about gas mileage. LOL!

Mark

[ga traveler]

I have posted this before. When we went out west in 2008, we had transmission troubles. (Look up changing the ground connections on transmissions on a 1999-2004 F53) we had to drive 55 mph from Washington State to Georgia. Never had a near miss or an accident. Not one hornblower. Not a single one finger salute. If others want to speed, that is on them, but please don’t say driving slower is dangerous. On moderate hills I have seen 18 wheelers going 40 mph. I have never seen a 18 wheeler rear ended. I can tell you for sure that coming over a hill and finding everyone stopped on the expressway can be real dangerous if you are speeding. That is why I slowed down to 60 mph.I topped the hill and there was traffic standing still. I was lucky, the median was clear, I hit the grass and stopped well past the last vehicles. You never know what is over the next hill.

[ArtJoyce]

We try to avoid I-95 from MD to NC. It travels to fast and much traffic. Someone slowes down and traffic comes to a stop.

We travel between 63 and 70, with the sweet spot at about 66 mph. We use cruse control only on the flat lands. We are shorter 36' and pull a kia soul. I travel at that speed to stay safe.

Our mpg runs on the low side of 8.5 and on the high side of 11 mpg. It's normaly right at about 9.5. We re-fuel most of the time at about 700 miles and are around 70 gallons, within 5.