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Old 08-31-2012, 11:05 AM   #1
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Aerodynamics

My gas mileage goes from 24 mpg(hwy) to 10 mpg when I tow my 154BH. As we all know, the Jayco is not a very aerodynamic unit and I was thinking about putting a roof top carrier on my Santa Fe in hopes of breaking the air resistance while doing 65 on the highway. Any thought would be appreciated?
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Old 08-31-2012, 11:20 AM   #2
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I really do not think it will make a measurable difference, if any at all. In fact, it could hurt your gas mileage even more. I think it's just a fact of life that pulling a TT will lower your gas mileage. I average about 8-10mpg pulling mine.
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Old 08-31-2012, 11:31 AM   #3
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Slow down to 60 or 55 and see what happens.
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Old 08-31-2012, 05:28 PM   #4
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Slow down to 60 or 55 and see what happens.
X2
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Old 09-01-2012, 05:02 AM   #5
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A large component in your MPG is frontal area of the trailer & tow vehicle. Wind resistance varies by the 4th power of wind speed. Increasing your speed from 50 mph to 60 approximately doubles your wind resistance and going from 60 to 70 almost doubles it again. If you want better MPG, you really need to slow down.

Without the trailer, car topping a canoe cuts our milage by 1-2 MPG. When towing the trailer, having the canoe on top of the car seems to cut MPG by about 1/2 MPG. My guess is that adding a car top carrier is not going to improve your MPG and may hurt it.
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Old 09-01-2012, 06:00 AM   #6
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X2
X3
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Old 09-01-2012, 07:26 AM   #7
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Forgot to add this, think about an egg placed between your foot and the gas petal, light pressure always, even when accelerating.
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Old 09-01-2012, 07:41 AM   #8
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Forgot to add this, think about an egg placed between your foot and the gas petal, light pressure always, even when accelerating.
We always called this bubble footin'. This technique and slowing down will make some difference. The bottom line is the TT is like pulling a parachute.

Your particular TV exhibits more of a mpg drop than others because the engine is working much harder than TV with a larger engine. My TV only drops about 3 to 4 mpg while towing but it has a tremendous amount of reserve capacity. In other words, it always gets low mileage, but it doesn't strain with the TT.

10 mpg is about average for pulling TTs with gas engines and after getting the rollingmass up to speed the size of the trailer doesn't make a great deal of difference.
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Old 09-01-2012, 09:36 AM   #9
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The first thing to do is get in the habit of driving slower and taking your foot off the accelerator earlier (coasting time) when coming to a stop. This will have a huge impact on your mpg.

With the TT, if I drive 70ish I get about ~9 mpg. If I drive 60ish, I get ~10.5mpgs, if I drive 55, I average around ~13 mpg. Without the TT, I at 70 mph I average about 17 mph, at 55 mph, I average bit over 23 mpg.

If you proceed, and you want it to have any positive effect you need to keep the angle below 45 degrees, otherwise it will work like an airbrake. Think of it as a ramp to jump a motorcycle (don’t forget the arc) and that should give you an idea where to place it. If you place it to far back with too steep of an angle the air will hit the ramp and slow down and cause drag. What air goes over it will hit the front of the TT causing drag. If it is too far forwards with too low of an angle, the air will slid over the ramp but will not be deflected high enough to overtake the TT’s front wall. There is a Mythbuster’s video (season 6 Car vs Rain) of Jamie and Adam driving a Porsche convertible with the top down through the rain. Their goal is to drive fast enough to keep the interior of the car dry. There is a high speed video that shows air currents pushing the rain over the cab, and virtually no water getting into the car. Surprisingly they did not have to drive all that fast to accomplish their goal. What you need to do is simulate the Porsche’s windshield on the roof of your SUV.

The key to do it is finding the correct position to make it work.
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Old 09-01-2012, 03:02 PM   #10
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Agree with just about all the above, and particularly with Boss Wagon. If your TV can loaf along at 60mph on a relatively flat interstate, it will get much better mileage than if it is straining to keep up speed. My F-350 V-10 gasser has no trouble towing an 11,000lb 5th wheel, which really IS like pulling a billboard, and on the level I can even let it go into overdrive without putting a strain on. It loafs until a long hill, when the OD comes off and it pulls steadily up the hill with a little higher RPM. As Boss Wagon mentions, my no-tow mpg is about 11-12, and it only drops to 8-9 with the 5er. The two keys to higher mileage are definitely higher TV capacity and lower speed, with aerodynamics a distant 3rd, IMHO.
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Old 09-01-2012, 05:27 PM   #11
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There are tons of threads like this, and the consensus I see is, it's all about wind resistance. Ask an over-the-road trucker how much improvement they get running the trailer full or empty. It's pretty close. RV TVs just get ten mpg towing. Not a whole lot of variance for most, except for the known guzzlers, like the V10. My dually diesel got ten average towing our toyhauler empty, 5800# and ten with two quads on it. Same truck gets ten average pulling about 9500# with the new TT. I've run at 55 for a mileage test and couldn't improve over the 62 I normally run. I imagine if I ran a thousand miles at 55 vs a thou at 62 there'd be a difference, but probably not enough to warrant the extra hours in the cab.

I get about 13 mpg pulling 7800# of hay that's only about a foot taller than my cap. The hay load has about a fourth the frontal exposure as the trailers. And I got right at 17 on a 1700 mile trip not towing. This is all just my read and my personal experience. Your experience may vary.
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Old 09-01-2012, 08:19 PM   #12
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Thanks again to all, Peace.
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Old 09-02-2012, 11:07 AM   #13
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cekkk - don't know about V-10s being "known guzzlers". Seems to me that my 11-12 mpg is every bit as good as others with averages of 10 mpg, don't you ? And when diesel is 70-80 cents higher per gallon than regular gas, well - you do the math. JMHO
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Old 09-02-2012, 09:49 PM   #14
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My Excursion--Wt 7360 pounds, Full of fuel, 75 lbs of toolbox. In town no tow 10- 10 1/2. On highway 13-13 1/2. Best was 16 mpg with tail wind. Towing with 9500 lbs of trailer 9-10 mpg going eastbound, 8-9 going westbound. If going into head wind can watch gas guage go down. But the Excursion does what I want it to do and it is paid for.
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Old 09-03-2012, 12:37 AM   #15
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6.5mpg to Disney and back!
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Old 09-03-2012, 11:02 AM   #16
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When towing the Heartland I had, even though it was about 1500 pounds lighter then the Jayco I got about 1-1 1/2 miles less per gallon. Because that trailer was about 14-18 inches higher. That made a differance when going into the wind.
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Old 09-03-2012, 11:41 AM   #17
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When towing the Heartland I had, even though it was about 1500 pounds lighter then the Jayco I got about 1-1 1/2 miles less per gallon. Because that trailer was about 14-18 inches higher. That made a differance
Or could it just be that you were running 85 on the 10 racing to Barro's?!?
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Old 09-03-2012, 12:18 PM   #18
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When walking around the campground recently, I happened to notice that a lot of other RV's steps looked to be higher off the ground(bottom step). I had recently purchased those metal step braces that screw up and down and that is why I happened to notice. Any who, are Jayco's perhaps a little lower to the ground or is it my imagination?
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Old 09-03-2012, 12:57 PM   #19
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Craig never thought about that. you could be right.
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Old 09-03-2012, 12:59 PM   #20
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krackeer yep on the heartland we had to buy a step that they sell at camping world cause of the height.
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