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Old 01-21-2022, 10:54 AM   #113
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Speed versus Torque

Quote:
Originally Posted by swduns View Post
I wanted to pin down for myself what speed to drive
It seemed like a simple question ,,, what is the most fuel efficient speed
It turns out I'm seeking a simple answer to a complex problem
I have a class A DP 2008 Tiffin Phaeton Cummins Freightliner 360HP (CM2150 8.3L)
The research made my brain bleed ... it depends ....
My conclusion ....
- How you accelerate is more important than speed ... just ease around
- 63 mph seems to be the anecdotal consensus although I'm not sure there is definitive research to support that particular number ... as again .... it depends

- has anyone definitively found the bona fide holy grail of current research that accurately answers this question or is the answer ... the impossible dream ... I suspect the definitive answer is ... it depends ...
I suggest looking at the Torque Curve of your specific motor. Mine is at about 1100 RPM in my Cat C7 which is about 61 mph.
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Old 01-21-2022, 11:08 AM   #114
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Old 01-21-2022, 11:10 AM   #115
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Quote:
Originally Posted by Ed Gardiser View Post
I suggest looking at the Torque Curve of your specific motor. Mine is at about 1100 RPM in my Cat C7 which is about 61 mph.

C7 peak torque at 1,100 RPM???
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Old 01-21-2022, 11:38 AM   #116
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Plan to move on the days and in the direction with, a strong tailwind.
ie. Ride like the Wind.�� ��
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Old 01-21-2022, 06:49 PM   #117
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If you all are worried about 60 vrs 65 vrs 70 on gas milage you shouldn't of spent the money to own one of these rigs.
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Old 01-21-2022, 08:07 PM   #118
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We get our best mileage between 55 and 65mph. The sweet spot seems to fall between 1400 and 1600 rpm.
Detroit series 60, 515Hp, 1650ft lbs, ZF 12 speed auto shift, 56,000 GVW, tandem drive.
We get 7.5 - 8.5 mpg towing a Ram 1500
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Old 01-21-2022, 08:11 PM   #119
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A difference of 1 to 3 extra miles per gallon is kinda small in the overall picture of things to be concerned about , like : why does the campfire smoke always follow me ? ; why when backing up , doesn't the wife just stand where you want your driver's side back corner to end up, and you just back it up to her ' and other " real " issues. LOL
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Old 01-22-2022, 06:56 AM   #120
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I don't agree with posts that say fuel economy doesn't matter. For instance if you get 6 MPH on a 500 mile trip you use ~83 gallons of fuel. At $3.50 a gallon that is ~$292. On the other hand if your MPG were 3 MPG better you would use ~56 gallons of fuel for a fuel expenditure of $194. In 500 miles that is a difference of ~$94.

For some people that $94 difference is insignificant but for others it makes a BIG difference.

The OP asked the question about the best speed to drive to get the best efficiency. Most responders to the question think he meant the best fuel economy and they answered based on their individual experiences. The OP has his reason's for wanting to know. To him it is important! Maybe it's the money, maybe he just wants to know. Either way answers that say it doesn't matter do not do a service to the OP nor this thread.

If he wanted to know if the forum thought that fuel economy was important he would have asked a different question.

That is my opinion! I still might get slapped for my opinion!
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Old 01-22-2022, 07:37 AM   #121
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^^^Are you suggesting that people actually answer the question that was asked?
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Old 01-22-2022, 07:45 AM   #122
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I didn’t buy a Motorhome to worry about fuel efficiency. Going a certain speed to save less than 1 mile per gallon doesn’t make much difference on a trip. If I wanted to save fuel I would buy a car and sleep in a tent
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Old 01-22-2022, 07:50 AM   #123
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Quote:
Originally Posted by swduns View Post
I wanted to pin down for myself what speed to drive
It seemed like a simple question ,,, what is the most fuel efficient speed
It turns out I'm seeking a simple answer to a complex problem
I have a class A DP 2008 Tiffin Phaeton Cummins Freightliner 360HP (CM2150 8.3L)
The research made my brain bleed ... it depends ....
My conclusion ....
- How you accelerate is more important than speed ... just ease around
- 63 mph seems to be the anecdotal consensus although I'm not sure there is definitive research to support that particular number ... as again .... it depends

- has anyone definitively found the bona fide holy grail of current research that accurately answers this question or is the answer ... the impossible dream ... I suspect the definitive answer is ... it depends ...
This may help - https://www.rvtechlibrary.com/engine...erformance.pdf

https://welove.com/wp-content/upload...el-Economy.pdf

Cummins also has a similar one to read - IMHO these two answer most of the Questions.

Good Luck,
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Old 01-22-2022, 02:05 PM   #124
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When you're only getting less than 10 mpg, 1 mpg improvement is a 10% improvement. I'm sure we can find other things besides fuel to spend money on. It's a good question and in general, many drive at around 61 mph as the best compromise between speed and mpg. YMMV
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Old 01-22-2022, 02:12 PM   #125
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Originally Posted by Busskipper View Post

Often mentioned in these excellent "white papers" is that the driver (good vs bad) can account for a 20% difference in MPG.


So, when you drive your car/light truck, how does your MPG compare with EPA figures? That will give you a starting benchmark for driving style.


I am sometimes shocked by those complaining about MPG on their diesel pushers who have no idea what "mode" is or how to use the engine brake most effectively without sacrificing fuel. There is more of an "art" to getting better MPG on heavier vehicles.
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Old 01-23-2022, 10:46 AM   #126
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I am not a vehicle expert, but 45 MPH is probably the optimal for MPG. ....a speed no one is going to do on a highway. I drove to Florida with my MDX towing a 4500# Jaopyco Micro 166FBS and was doing 65-70 most of the time getting 8.5 MPH, or worse through mountains. It's ~ 9.5 at 55, but I'm not going to drive that slowly!!. I know from experimenting with my (gas) V6's and V8's over the years, with and without towing trailers, that MPG starts to drop off pretty quickly above 65mph, worse on my MDX AWD than with the Suburbans in 2WD.
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