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Old 11-03-2009, 10:37 PM   #1 (permalink)
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Big project-F250 pulling 20x8.5 enclosed trailer

Getting 8mpg. Trailer weighs 7500# or so. It pulls very hard. It has 7' ceilings so is a bit tall. Top 3' is always splattered with bugs. I'm thinking put a topper on the truck. I have a soft tonneau now. I was also thinking about putting one of the adjustable wings on top of the topper at the very back. I'd really like a flexible sleeve that would connect the truck/topper to the trailer like a big sock. Not feasible now. I pull the trailer 2500 miles or so a month on average.

Looking at putting side skirts and moons on the trailer as the tires are tucked in the fenders. Diverters in front of the trailer tires?

On the truck, looking to block the grille. It is a diesel and getting cold, so it won't hurt to have it blocked off. What other easy things can I do to help out. Been reading a lot, but not sure where to start.

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Old 11-03-2009, 10:41 PM   #2 (permalink)
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Check out JacobAziza's posts, he's got a 250 diesel as well.

Yes to the topper, but try to find one that has a steady slope to just higher than the top of the trailer from the cab extension. The overall profile should show a slope from the cab roof to just higher than the trailer roof.
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Old 11-03-2009, 11:04 PM   #3 (permalink)
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Agreed on topper + deflector.

Also, side skirts like this:



After that the biggest gains are likely to be found at the rear of the trailer.

To reduce drag, you need to reduce cross sectional area of the turbulent wake you're leaving behind. That means a full or partial "boat tail" or add-ons that effectively taper the thing in profile & plan view. (EG. Note the tapering of the side skirts aft of the wheels in the above image.)

I've seen a photo of an inflatable, detachable trailer "boat tail" around, but can't find it at the moment.
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Old 11-04-2009, 09:35 AM   #4 (permalink)
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Interesting. They don't make toppers tall enough to go over the top of the trailer. That was why I was thinking of one of the adjustable deflectors at the back of it. I think the topper is going to help the most as it will greatly reduce the air hitting an estimated, 4'x8.5' area that is exposed from the top of the tonneau cover on the truck to the top of the trailer.

My wheels are already tucked in the wheel wells, ie, the fenders only stick out about 2" from the side of the trailer. I was thinking about just putting a skirt across them and putting moon caps on.
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Old 11-04-2009, 01:08 PM   #5 (permalink)
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How much do you care about aesthetics? If there are stake pockets in your bed sides, you can easily make a tube frame from aluminum of galv steel tubing and stretch thin canvas or something similar over it to get a smooth taper from cab extension to just above the trailer height, and it would be removable for when you're not hauling the trailer (if ever).

Inversely, you could make another one that tapers down gently from the cab extension to the tailgate, for when you're not towing the trailer, and just have a pair of cloth caps that you can easily swap out depending on your needs that day.

The spoiler will help as well, if you just want a regular cap on the back, but placement and angle will be key. If you require the flow to make a steep transition from the cap to the top of the trailer, it will not do much for you. If you move the spoiler too far forward, you will lose some of the benefit.
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Old 11-04-2009, 01:18 PM   #6 (permalink)
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I don't want it to look goofy, but don't mind trying stuff. I think a topper will be a huge help and then figuring out a deflector will be the best I'm going to get. Back of trailer is also square. Wondering about how to smooth the transition some. Would cutting 6" pvc pipe and installing it at the very top/back of the trailer help any? What about the same thing on the sides?
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Old 11-04-2009, 01:24 PM   #7 (permalink)
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Some people have tried saw-tooth edging on square edges, I haven't tried it myself, though, and haven't seen any evidence that it works.

Does the door open like a barn door, or does it fold down completely? (Assuming there is a door on the back of the trailer.)

Either way, you can add like a 2" extension that slopes 12* from the top, 12* from the sides, and probably not more than 3* from the bottom. You can make a sloping box out of it, that will decrease your cross sectional area substantially and help to train airflow to a close, rather than leaving a more turbulent wake.
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Old 11-04-2009, 02:09 PM   #8 (permalink)
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Door folds down like a ramp. I do have to use it some, so need something quick/easy to remove. They have the inflatable things for the big trucks, but haven't seem them for a small one yet.

I'm looking at camper shells. They have some that have a relatively smooth transition to about 12" taller than cab height. I think that would help a ton as it would be almost the same height as the trailer itself.
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Old 11-04-2009, 03:58 PM   #9 (permalink)
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Any chance you could post some photos?

Quote:
Originally Posted by 5.0 Junkie View Post
Back of trailer is also square. Wondering about how to smooth the transition some. Would cutting 6" pvc pipe and installing it at the very top/back of the trailer help any? What about the same thing on the sides?
Not sure what you're thinking of, in terms of mounting the pipe.

This would help:



The top & side extensions are tapered in at roughly 10 degrees.

Same angle as this quick 'n' dirty cardboard test done here, which improved MPG by 3.7% at 88.5 km/h / 55 mph.

Note the % savings will be greater the higher the speed.



See this thread for more info: http://ecomodder.com/forum/showthrea...-6-a-6069.html
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Old 11-04-2009, 04:33 PM   #10 (permalink)
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I'll try to get some pics. Trailer is at the storage place.

I have looked at some extended height camper shells and I think they would work nicely. The truck site I'm on had a guy that pulled a camper trailer a bunch and he picked up 2mpg by adding a camper shell. They aren't cheap, but with me pulling 2000+ miles a month at roughly 8mpg, it'd pay for itself in a year.

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