The Tortoise and the Hare

[RandyA]

Just a quick short story.  Our 670 is singled, has a D12 engine and pulls a 40' fiver weighing in at about 19K.  We were heading for Florida and my wife was pulling a small utility trailer behind her Equinox.  At first she refused to pull the trailer but agreed if I kept my speed at 62mph.  Heck, I'm getting old and driving slower seemed like a good idea any way.  From our summer home in Virginia to Florida's east coast is 888 miles.  No mountains and with the exception of South Carolina the highway is smooth and straight with few if any stoppages.  I held true to my word and resisted the temptation to pass 55 mph governed company trucks like lighting McQue - I just sat back, set the cruise control and listened to prime country on SeriusXM.  It didn't take long for the mpg reading to start rising from the 2mpg I earned while idling to warm up.  By the time we hit the Virginia/NC border I was up to 7.4 mph.  I held slow and steady the entire distance and arrived at our destination with 8.4 on the mpg clock.  Now, when I make this trip i usually run 65 to 70 mph, pass any slow vehicle and work the accelerator and 10 to 9 gear range pretty hard.  Mileage expected is something like 6.5 to 7.2.  The numbers work out like this:  That is 106 gallons of diesel at a current price of $2.75 & 9/10 a gallon that's $292.00 in diesel fuel to get here.  I I had NOT tried the slower speed and using my old numbers with today's diesel cost I would have burned 129 gallons of diesel fuel.  At today's cost that would be $356.00.  Or, said another was, 60 gallons less and a savings of $166 dollars.  The wife was happy, the trip less stressful and $166 is nothing to scoff about.  Driving the rig slower definitely saved fuel/money and I am sure made my trip safer. Of course it was a flat road trip with no hills or mountains.  Once I get into mountainous country  I general forget about speed or mileage and when all is said and done 6 to 6.2 mpg is OK.  I'm getting older and slower, but this time I am glad it worked that way.

[rickeieio]

Agreed, a bit slower saves fuel, but to me, the stress factor is higher priority.  In recent years, I've gotten into the habit of just running with the trucks in the slow lane when practical.  Slide in behind at a reasonable distance and gobble up the miles.  Trying to run 5 mph faster means more lane changes, thus more chances for a screw up.  I'd guess my average speed is something near 65-67.

We just got back from a round trip to Florida, 1900 miles round trip in my pickup.  It was the first time I used adaptive cruise control.  It worked pretty well, except when the vehicle I was following exited.  My cruise followed that vehicles speed, even though they were no longer in my lane, and would actually slam on the brakes.  I think the KW also has that feature, so it'll be a learning curve.

[lappir]

I try to do that very often, but then my truck seems to like it in the 70 to 78 mph. It sits in 10th gear and hardly ever downshifts. If I try to do the 60 to 62 it wants to shift at any hill, sure I could hit the manual button, but then it slows down on some of the longer pulls. I'm quite a bit heavier than a few of you. 

I had the Adaptive Cruise on my Subaru, the first month or two it seemed great. Then on the first trip out of town I was following someone and wondered why it was taking so long to get to the next town. The person in front had slowed from 67 down to 55 in the 65 mile per hour zone.  Seemed like every time I took a trip I'd find that same issue and the slamming on the brakes happens all too often making me put my foot on the gas almost all the time to avoid it. My Jeep has the regular old Cruise control and I am a happy driver again. 

 

Rod

[Darryl&Rita]

We're not even that old, and have been saying all along that if you're looking for fuel savings, look in the mirror. We routinely run around 62-65 mph and regularly get mid to high 10's for mileage. Got the HP turned down, while leaving the torque set high. N 14 just pulls.

[dennisvr]

With the speed limit of 55mph for trucks here in Calif. I have gotten used to running 60mph.  When I run other states with higher limits, I only run at 65. Much more than that and I feel myself tensing up, so I set the cruise and set back and enjoy the scenery. 

[Lou Schneider]

Gear fast, run slow has been a trucker's recipe for years.  Engines are most efficient right around their torque peak, which can be as low as 1400 RPM for a large diesel.  Air resistance goes up with the square of the speed so as you speed up you're spending more power to carve a large hole through the air.

My 1999 Ford 7.3L Powerstroke towing a 29 ft. Sunnybrook travel trailer gets 10-12 MPG at 60-65 MPH.  The truck has a cab height camper shell and combined with the relatively short trailer makes a fairly aerodynamic combo.

Edited December 17, 2021 by Lou Schneider

[GlennWest]

I get best mpg at 65. But that 1450 rpm

[SuiteSuccess]

Have always run 60-62 since the beginning. “I’ve got nowhere to go and all day to get there.”

[rickeieio]

1 hour ago, Lou Schneider said:

Engines are most efficient right around their torque peak, which can be as low as 1400 RPM for a large diesel. 

That's how our Volvo/Cummins ISX was.  It had a "happy zone" of about 1400-1600 rpm.  But if it smelled a hill and was at that 1400 zone, it would shift to 9th, unless I put it in manual mode.

That said, the KW has two little green dots on the tach where the sweet spot zone lies, and it's around 1100-1300 rpm.  We'll see in a couple weeks.......

[GeorgiaHybrid]

26 minutes ago, rickeieio said:

That's how our Volvo/Cummins ISX was.  It had a "happy zone" of about 1400-1600 rpm.  But if it smelled a hill and was at that 1400 zone, it would shift to 9th, unless I put it in manual mode.

That said, the KW has two little green dots on the tach where the sweet spot zone lies, and it's around 1100-1300 rpm.  We'll see in a couple weeks.......

The location of those green dots will depend on the engine, rear axle and transmission combo. On mine, it's 1400 rpm

[Danfreda1]

Same on ours, if it’s at 1400-1450 at the start of a hill it will just keep climbing. If it’s not that high it’s down shift time. 

[jenandjon]

68 seems to be my sweet spot. Anything under 60 I have to put it 9th gear or it lugs too much. I get 8-8.5 mpg pretty consistently. With my old smaller trailer, I averaged 9.

[mr. cob]

Howdy All,

Truck with Smart Car on board weighs in at 23,000 pounds trailer loaded is right at 20,000/21,000 depending on what toys are in the box.  Rear axle ratio is 3.55, Cat C15 single turbo 550 HP, 1,850 PT, engine and 18 speed Auto-Shift.

1,500 rpm in top gear ( 18th ) gives 72 mph road speed.  1,300 rpm gives 65 mph, 1,150 rpm gives 60 mph.  Average fuel mileage is 6.8 mpg driving the way I normally drive, up and down mountains all the time.  When it's safe to do so all things considered I run at 72 mph as in three years of owning and driving this truck it just likes to run at 1,500 rpm, anything below 1,300 it's not happy.  In 36,000 miles of western road travel to include MANY mountain ranges and high passes I have found that in my truck keeping the revs at 1,500 yields the best over all performance and mileage.  When driving in areas where It's best to run at 65-60 mph I split top gear and run in 17th or drop a full gear and go to 16th to keep the revs up and the Scan Gauge, shows this to be better for fuel mileage.

I made a promise to myself that when I got into RV'ing, "I" was NOT going to be that guy who everyone was cussing at when they had traffic backed up for miles or didn't have the power to pass when the opportunity presented itself. 

Would I like to get 10 plus mpg, heck yeah.  But to "me" the cost in frustration of being under powered, creeping up the grades and not being able to pass is just not worth it.  Then again I have been a speed, horse power and over all performance minded person my whole life so it just carries over into my choice of tow vehicle for RV'ing.  "IF" "I" were 30 years younger, there is no doubt what so ever that under the "Hood" would be a 1,000 HP, 2,250 PT, C16 engine that would probable get 5mpg or less and I could care less.  Does anyone need such a critter, heck NO, but then again do we really need a lot of things we want and enjoy.  Life is a short ride, none of us survive, enjoy it in every and any way you can.

Dave

[Larry Burkett]

Mr Cob, AMEN.

[Alie&Jim's Carrilite]

My lil' ole' M11 likes to run between 1500 and 1700rpm.  That difference in RPM is 65mph to 71 or so.  If we're running across the mid west plains, and have a head wind that is already penalizing us in economy, I'll kick it up and go.  Running across North Dakota, at 60mph we were getting 5.1mpg, sped up to 70 and got 4.9. That 10mph difference got us to our destination about 40minutes early, set up. enjoying a beverage in the wind....

[jenandjon]

1 minute ago, Alie&Jim's Carrilite said:

 enjoying a beverage in the wind....

Ugh I hate the wind. 

[RandyA]

As we all know - everyone's truck, sweet spot, road, driver, and load are different. With a little (actually a "BIG PUSH") from the XYL I thought it would be best on this trip to play "Follow the  Leader" rather than "Red Rover Come Over) and share my results.  It is probably a recessive gene in men to shrug off "intuition" from the cave keeper but she has proved herself right more times than wrong.
It is interesting to note several other observations about myself:  I had a radical prosectomy October 11 due to the discovery of cancer.  While I did not realize it a the time, my stamina according to my Urologist and Oncologist had begun to deteriorate "ME" - my body was using much of its energy to fight the cancer.   I became tired quicker and required more rest.  So driving slower and adding a day to our trip at each stop seemed reasonable.  While I ain't no Spring Chicken any more, my eye site is still 20/30 uncorrected,  my reaction time and memory (Jeopardy Standard) is still good.  I can hear anything I "want to",  but, I can't continue to hold my own with every young Rooster that comes in the yard".  I was a young 63 when I joined this net as a neotype in 2009.  I really have not paid much attenuation in to what has happened to my "facilities" as the years rolled on.  We must be realistic and accept that like a bucket of paint with the lid not tightly replaced our bodies and minds really are getting older and we need to first accept the problem, asses the severity of the changes and plan our travels in these beast of ours accordingly

[rickeieio]

Randy, You have aged like a fine wine.  While some of us, me included, are aging like milk.

[jenandjon]

11 hours ago, rickeieio said:

Randy, You have aged like a fine wine.  While some of us, me included, are aging like milk.

Turning into cheese? Cheese goes with wine. Close enough. 

[GeorgiaHybrid]

13 hours ago, jenandjon said:

Turning into cheese? Cheese goes with wine. Close enough. 

Nah, Rick is like buttermilk, he's just getting a little thick. 😎

[Darryl&Rita]

1 hour ago, GeorgiaHybrid said:

Nah, Rick is like buttermilk, he's just getting a little thick. 😎

I think the kids are spelling it thicc.

[GeorgiaHybrid]

6 minutes ago, Darryl&Rita said:

I think the kids are spelling it thicc.

If you follow the link you posted, it mentions "sexy curves". Have you ever met Rick???🤣🤣

[rickeieio]

Sheesh.  I just got home from a family Christmas gathering, and I didn't get nearly that much abuse.

But when I look in the mirror, I definitely see "thicc".

[Darryl&Rita]

10 hours ago, rickeieio said:

I didn't get nearly that much abuse

I tried to help, I really did. 😃😄

[rickeieio]

17 hours ago, GeorgiaHybrid said:

If you follow the link you posted, it mentions "sexy curves". Have you ever met Rick???🤣🤣

Obviously, he has.    ROFL