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Old 08-31-2012, 12:05 PM   #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, 12:20 PM   #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, 12:31 PM   #3
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Slow down to 60 or 55 and see what happens.
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Old 08-31-2012, 06:28 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, 06:02 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, 07:00 AM   #6
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X2
X3
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Old 09-01-2012, 08:26 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, 08:41 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, 10:36 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, 04:02 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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