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Old 06-23-2015, 03:38 AM   #1
JandC
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Biggest Factor Reducing My MPG

For almost 3 years of full timing using our 2012 F350 (6.7 diesel) we have averaged overall right at 11mpg.

When we had the 2008 3400RL we were averaging just under 12mpg. With the 3725RL our average is just barely 11mpg, but overall it is a solid 11mpg.

We pulled a loaded 24' enclosed trailer (loaded with furniture) from Illinois to Florida last week. It was a 1335 miles trip over 2 days. I never went across the scales but based on my empty trailer weight I would guess the loaded trailer by itself weighed around 8,000 pounds.

I got an average of 12mpg for the whole trip!

Of course the differences are the Montana weighs just under 16,000 pounds, but is a fiver and has a rounded front nose. It is 13'5" high to the front air.

The 24' enclosed trailer is obviously a pull behind, squared off front nose, and is just under 11' high.

I expected to get closer to 14 or even 15mpg pulling the trailer. I am thinking the square front killed my mpg and the weight really didn't make that much difference. Or is it the fact that a fiver being pulled just gets better mpg than a pull behind?
 
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Old 06-23-2015, 03:53 AM   #2
Virginia Young
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Back when I was pulling horse trailers, I noticed that there wan't much difference in mileage between a three-horse bumper-pull with a "V" front and a four-horse, living quarter, gooseneck with the flat front. I think it's just putting a load on the diesel truck. Doesn't seem to matter how much the load is. It was always the speed that made the bigger difference.
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Old 06-23-2015, 03:59 AM   #3
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My thinking is the combination fiver, nose just behind cab, with good aerodynamics just gets better mpg. With that bumper hitch and square box back here the turbulence forming behind the cab and box would almost create drag I would think???

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Old 06-23-2015, 06:05 AM   #4
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I don't understand why its that way, but I also have noticed almost the same type of millage regardless of what I'm pulling, I believe its where the peddle is in reference to the floor theory.
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Old 06-23-2015, 07:32 AM   #5
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With us it's all speed and gearing. With our truck 60mpg is the best fuel mileage and yes, flat fronted trailers will cost a couple of mpg.
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Old 06-23-2015, 08:50 AM   #6
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I always thought the biggest factor for my poor gas mileage was dragging that 14000 pound mountain that I see in my mirror :-)
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Old 06-23-2015, 09:30 AM   #7
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In my experience, the two biggest factors that reduce mileage are speed and wind resistance.
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Old 06-23-2015, 01:36 PM   #8
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Quote:
quote:Originally posted by DQDick

With us it's all speed and gearing. With our truck 60mpg is the best fuel mileage and yes, flat fronted trailers will cost a couple of mpg.
WOW!
Is that with the 1.08 Liter Cummins powered RAM 2500?

I only average around 11mpg when towing the Montana with my 5.9 Cummins powered RAM 3500. Maybe I should do a motor and differential swap, as I would like to get 60mpg too!!! 58mpg towing the big, flat-nosed cargo trailer would be great too.


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Old 06-23-2015, 01:58 PM   #9
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From my classroom Physics days, ahem, wind resistance is equal to the square of velocity at some speed. Go faster, it is the cube and real fast it is 5th power. I think those higher numbers would involve speeds over 100 mph or higher.
On a more practical note, I recently pulled across southern arizona and new mexico. I got around 8 mpg, if I recall until about noon. That is where we changed from a SE direction to straight East and also noted that the wind died down a bit. So the next 200 miles I got around 10.5 or so. So for a flat highway without stopping, I vote for wind resistance (directly related to speed plus actual wind). Of course in town withOUT towing, I only get about 15 doing stop and go traffic - even if I use the old 'eggshell' under the foot method. Every stop and start lowers the mpg by 1-3 points.
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Old 06-23-2015, 04:43 PM   #10
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Quote:
quote:Originally posted by JandC

For almost 3 years of full timing using our 2012 F350 (6.7 diesel) we have averaged overall right at 11mpg.

When we had the 2008 3400RL we were averaging just under 12mpg. With the 3725RL our average is just barely 11mpg, but overall it is a solid 11mpg.

We pulled a loaded 24' enclosed trailer (loaded with furniture) from Illinois to Florida last week. It was a 1335 miles trip over 2 days. I never went across the scales but based on my empty trailer weight I would guess the loaded trailer by itself weighed around 8,000 pounds.

I got an average of 12mpg for the whole trip!

Of course the differences are the Montana weighs just under 16,000 pounds, but is a fiver and has a rounded front nose. It is 13'5" high to the front air.

The 24' enclosed trailer is obviously a pull behind, squared off front nose, and is just under 11' high.

I expected to get closer to 14 or even 15mpg pulling the trailer. I am thinking the square front killed my mpg and the weight really didn't make that much difference. Or is it the fact that a fiver being pulled just gets better mpg than a pull behind?
You're retired aren't you...????
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Old 06-24-2015, 01:28 AM   #11
JandC
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Quote:
quote:Originally posted by DarMar

My thinking is the combination fiver, nose just behind cab, with good aerodynamics just gets better mpg. With that bumper hitch and square box back here the turbulence forming behind the cab and box would almost create drag I would think???
I think DarMar hit it on the head. I guess I was just considering my 24' pull behind had a flat nose. I think it would make a huge difference since it is located about 10' from the back of my truck cab, unlike my Montana which sits just a new feet away from my cab.

Yes Jay, I am retired. That is probably why I even take the time to compute my MPG or even think about it after swiping my card at Pilot.
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Old 06-25-2015, 02:04 PM   #12
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There's not really just one answer to this one as there are several factors involved here. The frontal area of the trailer and the truck both have contributions, but you also have to consider the peak engine performance of the truck, the environmental conditions (wind direction & speed, temperature, humidity, etc), the friction factors of both the truck and trailer, and a few others. Most of these factors go well beyond this discussion. Since we all have very little influence over most of these conditions, the one thing that we can control the most is vehicle speed. The force of the air against the frontal area of the truck/trailer, multiplied by velocity (speed) we are traveling determines the force of the air against the vehicles. So, the bottom line here is if you want to improve your MPG, slow down. My experience with our set-up is that 60 MPH works best for us (~13 MPG pulling the Monty). (Oh, and yes, I'm a Mechanical Engineer! Sorry...)
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Old 06-26-2015, 02:14 AM   #13
JandC
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While pulling the 24' enclosed trailer I kept my speed between 62 and 65mph. I had just had new tires installed and wanted to keep my speed down because they weren't the most expensive tires. I have always pulled the Montana in that same speed range.

I am sure you are right Ted when you point out that there are many factors effecting mpg. It just seems the one that makes the most logical sense to me in this comparison is the square nose difference and the fact the trailer sits back further compared to a fifth wheel hitch up.
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