Air deflectors for the top of the truck: good idea?

[Philsauto]

I have seen very few tow vehicles with spoilers on their roofs. Yet all of the modern trucks are equipped with some kind of an air deflector. My fuel economy drops almost in half when I am towing my 12,000 lbs 5th wheel. I'm wondering how much of the drop is due to wind resistance. BTW, I think I loose one mpg for every 5 mph over 55. I can watch the turbo boost go up steadily as I try to increase speed. At 70mph I am running around 12 lbs of boost and getting no better than 10mpg, where I can get 18mpg at 70mpg without the trailer. I'm wondering if a spoiler would help. Any thoughts or experience with same?

[chipper]

Yes, they help if it is big enough. After towing about 20,000 miles with my 79 Chev, I put one on & average for the next 40,000 miles towing was a solid 1 to 1.5 MPG better. I was towing a 30' 5er weighing 9500 lbs.

[Philsauto]

Yes, they help if it is big enough. After towing about 20,000 miles with my 79 Chev, I put one on & average for the next 40,000 miles towing was a solid 1 to 1.5 MPG better. I was towing a 30' 5er weighing 9500 lbs.

Chipper, can you make any recommendation as to where to get one? Would something that clamps on be sufficient? Thanks!

[chipper]

Chipper, can you make any recommendation as to where to get one? Would something that clamps on be sufficient? Thanks!

Does your truck have rain gutters above the cab door?

[David Utz]

Can they work? Yes, but only if the conditions are right. I got one for my last truck, a 90 K2500 gasser. I was pulling a mid-profile 5er and would run out of power on hills or a good headwind. The deflector is from camping world, the largest fiberglass wing they sell. It mounts on a bed mounted frame bolted to the front stake pockets. On that truck it gave me 10 to 15 MPH on the top end. It made the truck much more livable. Then came the 2001 Dmax, and then the high-profile trailer. The deflector for this combination is useless. It gives no notable benefit. A frontal picture will show only a tiny portion of the front of the trailer is covered by the deflector. It is about 12 square feet and the trailer is showing about 48 square feet. It is not wide or tall enough to make any sizeable difference. The bug splatter shows that it just can't move the air over or around all that frontal area. For them to work well, they need to be almost as wide and as tall as the trailer and mounted as close to the trailer as possible. With today's 12 foot tall 5ers, forget it.

[Philsauto]

Well, I guess we will have to see what happens. I bought a unit from Camping World yesterday after having read several forums. My 5th wheel is not 12 feet but it is 10ft. I know that because a I ran it into the door of my shop at 9'9" and tore a nasty gash in the aluminum right up there near the top. You are one of a variety of responses that says it doesn't help but there were quite a number who said they recognized some benefit, so I thought I would try it for myself. I leave next week so I can let you know soon if it did any good.

[Robyn]

One of the big things is the fact that most of the big trailers are about as aerodynamic as a barn.

The stress on the wing is tremendous at speed so I would not even recommend a clamp on unit.
The wing has got to cover the entire frontal width of the trailer to be able to lift the airstream up and over.

One thing that I have seen more and more on the class 8 stuff is the "Bubble" on the front of trailers.

These tend to allow the air to flow off and around easier than the usual flat frontal exposure.

At any rate the improvement is going to be noticeable if the wing or bubble can lessen the drag to a great enough degree.
As speed increases any device is going to be put to the test.

The shear amount of raw power that it takes to move this kind of weight at speeds over 55 is enormous and your going to have to feed the pony if you want him to work.
The generated heat is going to go up as is the EGT, water temp and so on.
You may wish to look into a splitter for the front of the trailer to get the wind around the beast as opposed to up and over it.

I would imagine that the air drag at higher speeds can be in the many many hundreds of pounds of force, sort of like driving on a really wet road pushing water with all the tires.

Tough call on this one but some judicious research into the products available should net you some good choices.

IMHO many of the wings are to be rated strictlly on the "LOOK COOL FACTOR"
I have seen some huge wings on big fancy Petes and KW's and have asked ther owners if they can really tell the difference. The answer is usually ambiguous at best but the "IT Looks Cool" seems to be the biggest thing I hear.

Im sure they all help some BUTTTTTTTT does it pay for itself??
I dont know.



Good luck

Robyn

[Inspector]

Another factor that adds to the drag is the vacume created at the back of the trailer as it moves throught the air. I have seen deflectors that are mounted to the verticle edges to force the side slip stream into that void. I have no idea of the benefit. I do know that a problem does exist.
Denny

[Robyn]

I think the Old airstream design did a lot of calcs on the flow dynamic.
As far as being spacious inside, probably not but I think they did/do tow good.

The more apendages there are on the top and sides as well as anything else that creates turbulence that is going to impact how slippery the thing is.

Robyn

[qinlet]

I used a air deflector on two different trucks and 5th wheel trailers. I had a 30ft Prowler 5th and pulled it with a 93 Chev 454 and I gained maybe 1 mpg or so I thought. it did seem to pull a little easyer and it did keep the front end of the camper cleaner but a big improvement in gas mileage is usually in the eye of the beholder and I did not see much. it is a good conversation starter. I then got a Jayco 35ft 5th wheel with a very smooth and low air resistant front end and rounded end cap and other than keeping the front end clean i thought I lost gas mileage, so the air deflector hit the junk heap and I never missed it. then I moved up to the 02 2500hd duramax and drive 68mph and get 11 to 12 mpg. The answer is to get a trailer with a aero slipery front end and rounded back end and air deflectors will be a thing of the past. if you look at the 18wheelers the trailer they pull has a flat front end and creates a lot of drag at 70mph so they have to use air deflectors. they may only save 1/2 mpg but if your fleet uses 3 million gallons of fuel a year that 1/2mpg will give the CEO one hell of a big bonus. The wings put out by a company in CA do look pretty neat so if appearance is more of what your looking for, i think the wings look pretty impressive.

[Philsauto]

Thanks for you information. Mine is a 2001 2500HD Crew Cab. Truck and loaded trailer together tip the scales at 20,000 pounds and I get 10mpg towing at 63mph. I have installed a wind deflector on the roof as the front of my 5th wheel is not very aerodynamic. I leave tomorrow for 1000 mile trip so I should have some solid results on the gain or lack of gain in mpg. I will post when I know.

[cowboywildbill]

There is also a lot of drag from the air trapped under a truck and trailer and roadway. The lower the vehicle the less drag. Also remeber when you run a deflector it may well help reduce drag while towing. But if you drive with it in place and your not towing then it is producing more drag than your truck would normally have empty. And if you drive unhooked a lot that might cancel out any gain.

[Philsauto]

Cowboy,

The unit I bought folds down when not in use, but the best bet will probably be to remove it. I'm really pleased with the fuel economy on this truck when not towing. It get as good of gas mileage as I got with my 1994 Dodge Dakota 3.9V6, maybe even slightly better on the road and definitely better when towing my 17' boat. But that 10mpg does hurt over the long haul with the trailer and if I can pick it up by 1mpg, at over $3 a gallon for diesel, it won't take that long to get a pay back on the cost of the wind deflector. If it makes no difference, well, I guess I will have learned something at least.

[cowboywildbill]

True and fuel probably isn't going to get any cheaper. We just towed our 40' LQ horse trailer to Columbus OH to the All American Quarter Horse Congress. I am pleased with the milage we averaged 9 or 10 mpg comming out. The trailer was about 14,500 lbs.
The DIC was reading 8 mpg in the mountains. But by hand calculation about 9.5 mpg for whole trip. It is a lot of big hills. The cheapest fuel we saw was $2.99 gal US$. We don't have a deflector, but our trailer isn't as tall as most fifth wheel campers are and I don't think it would help us that much, but who knows it might. We had a pair of Firestone air bags and compressor kit installed on our truck today. We are at the OH Expo Center and this place is loaded with truck and trailer dealers and aftermarket "you name it" dealers and vendors and Cowboy stuff. It's to the Cowboy's what Bike Week is to the Motorcycle Crowd. I'll put a post on the Accesories page about the bags after I tow with them. Our trailer pin wieght is 4,100 lbs. on the goose ball. Hopefully the bags will help. Keep us updated on your experiences with the deflector. Be safe.

[Philsauto]

Well, the jury is in. The wind deflector has a definite effect for the better. Average fuel economy between Hemet, California, and Ogden, Utah was 12.2 mpg overall, a measurable increase from the 10 mpg I was getting before. I ran into a stiff headwind between Ogden and Pocatello, Idaho, and I could tell if was costing me mileage just by watching the gauge. I haven't filled the tank yet so I don't know how much, but suffice to say, I am pleased with the results. At an average price of $3.22 a gallon, a 20% increase in mileage is a big deal. Thanks for all the suggestions and information.

[SeaFox236]

I am considering getting a wind deflector for my Yukon XL Denali to see if it will help when towing a 24 foot Center Console Boat with T-Top. Any suggest or ideas if this will work or is it not worth the money? Any ideas or suggestions would be appreciated.

[Philsauto]

Report on fuel savings using the wind deflector for the entire trip, Hemet, California to Aberdeen, Idaho and back:

2335 miles total, 95% of the time towing the 5th wheel, 32' Forest River Salem, fully loaded estimated weight around 12,000 pounds, used 186.3 gallons of fuel at an average cost of $3.35 per gallon (prices went up significantly between leaving and returning.) Average mileage for trip: 12.5 mpg. Average mileage before installing wind deflector 10 mpg. Fuel saved: 49 gallons. Money saved: $163.

As the deflector cost about $280 (Camping World), I should see a return on investment very soon. The thing rattles a bit in the wind, but we soon got used to it.

As to comments on another post on exhaust temps and fuel savings; there is a direct correlation between speed, load and exhaust temp. If I was to go with the desired 650-750 degrees of exhaust temp (pyro located in rear of right side manifold) for best fuel economy, I would have needed to keep my speed between 50-55mph. I did not try to do that but did try to keep my speed under 65 mph. Driving faster is stressful.