I went from pulling an approximately 8k mid profile 5'er @68-70 mph to pulling a 14k high profile 5'er @ 62-65 mph....and the mileage stayed to same. Towing mpg is 10.5 to 11.5. TV is a 6.0 powerstroke (stock except for egr mods).
Frontal area, how smooth the road is, what direction the wind is blowing, how well your tires are inflated, how worn your tires are, your transmission gear and speed, whether the torque converter is locked down, and the air temperature, and even how clean/smooth your surfaces are, and how rounded the corners on your rv are, the aerodynamic drag patterns, how smooth the bottom of your vehicle is, whether your windows are up or down, the grade profile of the trip, the effective cetane rating of your gasoline, and the compression of your engine, even how clogged your grill is with bugs and whether or not you're running the air conditioner.
So on the massive list of factors, where does 'overall weight' stack up in terms of magnitude? Closer to the bottom than most people assume. This also means that any measurement whose accuracy ( +/- half gallon on a fillup? ) is low can entirely overwhelm most of the factors.
I hypothesize that my inaccuracy in filling the tank to exactly the same level introduces significantly more change in my mileage calculations than the weight of what I am towing.
Factor? Sure. But concentrating on that is missing the main drag components. Hypermileage your trailer by smoothing the airflow around the corners and window frames, put fairings around your exposed plumbing, make a smoother transition between the truck and the trailer, reduce the drag caused by a big flat rear end. I hypothesize that adding 500 pounds to your rig in terms of fairings, vanes, and such would cause a far more noticeable fuel consumption rate change than changing weights. Even crossing the rockies.
Wind is the factor and it is derived by SPEED which impacts RPM and therefore the amount of FUEL your motor burns. We tow at 55 mph all day long and average 13 mph (have for the last 2 years full-timing). The weight of the rig does have an impact but only to a certain degree. You will see a bigger impact if you drive stop and go with the two rigs.
Our Challenger has an aerodynamic appearing (not sure if it is or is not) front cap that presents a streamlined face into the wind.
The worst gas mileage we ever measured was on a trip into a head wind when I tested out traveling at 65 mph = 11mpg.
Also note the newer diesels do get lower gas mileage than the prior to smog rules '07 and older trucks. I have also found that the additive "Diesel Kleen" gives us a nice boost.
For comparison sake we average 23 mpg around town with our truck unhooked.
Interesting replys....No, we did not trade down for better MPG, we fulltimed for two years in a 38 ft,4 slideout rig and decided to trade for a smaller one for our two or three months trips. I'm really not stupid, I was just asking a simple question.lol Thanks for so many quick answers.
larrygranny, i did the same thing, 38' to 28'. sure thought i would see some difference in mileage. nothing changed. emission stuff on my '07 dodge 6.7 has a lot to do with it. towed the 38' with 7.3 ford and mileage was better.
Your mileage is based upon two items. One has been mentioned, wind resistance which is a function of the front end square footage. The second is based on the rear end ration you have. A high rear end numeric value (i.e. 4.88) gives lower mileage than a low number (i.e. 3.73). Once you have used your torque to get the 5'er moving these determine your mileage more than the 5'ers weight. Since you used basically the same route, neither rolling resistance, road slope nor shock function factors in as they were the same in both instances.
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