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Old 06-10-2013, 06:10 PM   #43
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Free mass hauling! I'd bet the trucking industry would love to discover this!
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Old 06-10-2013, 06:16 PM   #44
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I agree mathematically there's going to be a slight reduction in mileage - more weight means more fuel; the physics are that simple. But practically it's probably not going to make a major difference; it'll be "lost in the noise" as statisticians say - during any given trip, dozens of things will affect your mileage, too, so it's hard to tease out a small increase or decrease attributable to any one factor.
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Old 06-10-2013, 06:26 PM   #45
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That is true, Skater, and more "lost in the noise" with larger displacement TVs, which are already wasting more energy than a small displacement engine simply by it's design. They are designed to be more energy efficient under load(strictly speaking from a physics efficiency standpoint, not to be confused with our colloquial use of the word).

Now if you add 60 gallons of water to an already stressed TV (some would say overstressed) like a minivan pulling a 30'er, you would see, on a percentage basis, a larger mileage penalty.

Likewise a diesel, or the 454 referenced above would realize a lesser penalty on a percentage basis.
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Old 06-10-2013, 07:43 PM   #46
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Typically we carry some water, enough to flush the toilet and wash the hands when in route to a destination. My fresh water tank is 60 gallons and quite honestly with food, clothing, and a slide out, that 9100 lb gross doesn't leave much room. We do one trip a year where we don't want to use the campground water. That trip is pretty much a flat land trip. So we depart with a full tank. Would I want to drag a full tank when I head out to Branson? No way. I have to gear down to get up some of those hills at a reasonable speed. I'd hate to think what carrying another 500 lbs of liquid would do.

But as far as the trailer goes, it was built to run with full water tank, so don't be fearful of that. Just make sure you understand that the water weight is one component to consider regarding your trailer's gross weight capacity.

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Old 06-10-2013, 08:06 PM   #47
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When I pur. 2000 chev. 6.0 liter gas I got 18 mpg now with 53,00 miles avg. 10 mpg engine is in top tune. I have always towed 70 to 80 mph. This a big Q. Why? G.M cannot answer. Also towing back hoe or other Impl. same story. May be Rich [dznf0g] can answer. also never since 1962 towed w/tanks empty & never dump when leaving camp grounds until get home, fertz. corn & beans [same wgt. out same wgt. back]
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Old 06-10-2013, 08:10 PM   #48
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I'll PM you.
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Old 06-10-2013, 08:16 PM   #49
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I'll PM you.
It won't let me open the pm call me 630 554 9409
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Old 06-10-2013, 08:21 PM   #50
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emailed you....don't want to hijack the water thread.
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Old 06-10-2013, 08:47 PM   #51
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Once you reach highway speed, the output of the engine must balance the rolling resistance and the wind resistance of the rig. Rolling resistance will change with added weight, but wind resistance will not. I believe wind resistance to be the dominate of the two factors at highway speeds.

This is why speed is such an important factor in your mileage, as there is a non-linear relationship between the two. Doubling the speed of your airstream requires 8 times the power.

So I would think a change in mileage due to extra weight would be more apparent while city driving (lots of acceleration) versus steady state highway driving. Shedding weight in a vehicle is important - but not so much on long hauls.
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Old 06-10-2013, 08:54 PM   #52
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Once you reach highway speed, the output of the engine must balance the rolling resistance and the wind resistance of the rig. Rolling resistance will change with added weight, but wind resistance will not. I believe wind resistance to be the dominate of the two factors at highway speeds.

This is why speed is such an important factor in your mileage, as there is a non-linear relationship between the two. Doubling the speed of your airstream requires 8 times the power.

So I would think a change in mileage due to extra weight would have more impact in city driving (lots of acceleration) versus steady state highway driving. Shedding weight in a vehicle is important - but not so much on long hauls.
Yes, all true. In addition, elevation changes will impact MPG in direct relation to weight. It does take some additional energy to keep the mass rolling, but not nearly as much as acceleration and hill climbing (not necessarily mountains either). All of this discussion should be made in terms of long term mileage figures. Any particular day of even long hauling on flat territory could be different than the next day, due to the other factors at play, like wind, given the same weight.
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Old 06-10-2013, 09:27 PM   #53
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What!!! No mention of a "Body in Motion tends to stay in motion and one at rest tends to stay at rest."
I say! "If you can't afford a few tenths of a gallon. Then maybe you should stay home"
Based on all of this physics stuff. It would be better to travel in 100+ degree temps. Because the air is thinner and there is less wind resistance. Than at night or in cold places where it is thicker. But engines get less efficient in the high temps. So there you go! You should probably just stay home.
If you travel the same route going and coming. The up hill battle should be offset on the return trip by being able to use the "body in motion".
I find it amazing that anyone thinks like this when on vacation.
A person could drive their self nuts with stuff like this.
How much is the bug shield costing me on MPG? What about the radio antenna?
How much is the satellite receiver costing me in wind resistance?
What about the A/C? The vent covers?
How 'bout the awning arms?
Or the fact that the back of the TV and coach are pretty much flat? When maybe a boat tail would get me a couple of tenths.
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Old 06-10-2013, 09:33 PM   #54
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I only think about it while on the forum...not on vacation. By the way, I presume you read it all???????? How sick is that?
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Old 06-10-2013, 09:44 PM   #55
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Yes, the math IS the math. If you calculate using a calculator to many decimal places you may think that the water weight is impacting your mileage. If you do the math using a slide rule much less so. When traveling the water is optional until you need it. I always travel with at least 1/2 tank. Sometimes a full one. You never know when you'll need it.
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Old 06-10-2013, 09:48 PM   #56
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I hear ya Roger, And I load everything I want, including water. I just HATE overarching opinions like "traveling with a full tank of water has no impact on fuel economy". It is opinion expressed as fact that a newbie will adopt as fact. Truth is: ALL weight impacts fuel economy....every pound equally, water or steel or rubber............
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