wind deflector improves gas mileage - Fiberglass RV


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Old 11-21-2013, 05:06 PM   #1
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Smile wind deflector improves gas mileage

Hi all,
I thought I would tell you about my recent adventure with gas mileage towing our 1980 Trillium 4500. The trailer weighs just under 2000 pounds fully loaded for camping, including hitch weight. However, it has a square front that feels like a sail when towing. We have been thrilled with our trailer for the past 3 years, other than gas mileage while towing, which appears to be somewhat worse than our former Boler (which was 500 pounds lighter and rounded on the front).

I have seen on many forums over the years the generally expressed opinion that wind deflectors do not work. However, I also noticed that virtually every large truck on the highway has one. So, I thought I would give it a try. I considered mounting it on the trailer itself, but it seemed easier to mount it on the back of our minivan, using the roof rack rails. I bought a plastic folding table at Costco for about $30, and mounted it on the roof rack at the back of my minivan with brackets so that it could be lowered when I am not towing. After my proof-of-concept test, I painted it to match the van.

The attached pictures sort-of show how it is made. I cut notches in the front of the table edge so that it would fit down onto the roof rack rails. Then I mounted the table to the roof rack using sliding rail fasteners for my roof rack that I got at a wrecker for free. These are the same mounting brackets that usually hold the roof rack crossbars. Instead, I drilled a hole through it and installed a bolt facing inward that I could put a wing nut on. On the front edge of the table, I installed an “L” shaped metal corner so I could attach the table to the roof rack fasteners. When I cut the table it was hollow, so I put a small block of wood inside the table edge so it would not get crushed when I bolted on the “L” corner.

I wanted to be able to raise and lower the table at the back so that I could lower it when not towing. So, I got another pair of roof rack mounts to attach it to the roof, with another “L” corner bolted on to the table top. Attached to the “L” corner with a rivet is a length of perforated metal shelf support, so that I could adjust the height if I wanted. After the first day on the road I had to break the strip down to a shorter length because my initial angle of deflection was too high and detracted from our gas mileage. It turned out that the rear pair of brackets was not necessary as I was able to mount the rear brace by drilling a hole directly through the back roof rack mount. This was OK because when I lowered the table I wanted it to be as far back as possible without interfering with raising the rear van door. It turned out to work fine with one fixed point at the rear arm, and one moveable point at the front.

So, how did it work?

Before I put the wind deflector on, I was getting anywhere from 16 L/100KM on a really good day to 21 L/100KM travelling against the strong prairie wind, usually in the 17.5 - 19 range. That translates to: 17.5 L/100KM is 13.4 US mpg, 21 L/100KM = 11.2 US mpg. Not very good. In addition, it felt like towing a brick wall, and the trailer was always plastered with bugs along the sides and top where the outline exceeded the profile of our minivan. When not towing, our gas mileage varies from 9.9 L/100KM in perfect conditions to about 16 against the prairie winds.

Afterwards, on our 7000 KM recent trip in the US, my gas mileage improved dramatically. The first day was a bit tough because the initial angle was too high and then when I tried to adjust it I could not get the right angle, hence the breaking of the metal arms the next day. However, it was still better than not having it. That day we got an average of 14.1 over 950 KM. Gas mileage then varied from about 12.4 in perfect conditions to 15.9 when going up steep mountains at 8500 feet and against strong winds. Overall, over about 5400 KM that we towed the trailer we averaged 13.5 L/100KM, including the first day and including all the weather and road variations. That translates to 17.4 US mpg.

Here in Alberta gas costs about $1.10 per litre at the time I did the trip, which is by far the cheapest in Canada. So, I am saving anywhere from 3 to 6 litres for every 100 KM (62 miles) that we tow. This is all at 65 mph, which is about 103KM/hr.

In addition to gas savings, the feel of the trailer while towing was noticeably better, in that it was very stable and no longer felt like towing a huge sail. There were also virtually no bugs on the roofline after several weeks on the road, whereas before they would be plastered all over in an outline of the tow vehicle. Both of these are non-economic benefits.

Because I installed it using a few bolts and wing nuts, I was able to easily remove it and hang it on the wall in our garage for the winter. It weighs very little. However, the wind deformed it a bit into a “smile” at the center over several weeks, so if I was going to do it again I would adapt the metal table legs that came with it to stiffen the plastic table top.

So, I would highly recommend it.

Rick G in Alberta
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Old 11-21-2013, 05:16 PM   #2
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Name: Steve
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I'm glad this worked out so well for you. I got poo pooed when I brought it up a couple of months ago. I am planning to set up the same test the next time I take a decent trip.
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Old 11-21-2013, 06:11 PM   #3
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Great idea and great job.
Thanks for sharing.
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Old 11-21-2013, 06:16 PM   #4
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Quote:
Originally Posted by stevebaz View Post
I'm glad this worked out so well for you. I got poo pooed when I brought it up a couple of months ago. I am planning to set up the same test the next time I take a decent trip.
Never let getting poo pooed stop you. If the arguments don't make sense to you go for it. Then post your results. Personally, I can't see why this would be considered a bad idea.
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Old 11-21-2013, 07:40 PM   #5
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Although the ones used on OTR trucks will run in to $1000's, if they allow as little as .1 mpg extra, they can pay off in less than a 1/4 million miles (I think)
Your improvement was significantly better.
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Old 11-21-2013, 08:38 PM   #6
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Rick, Great experiment. Good for you!
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Old 11-21-2013, 11:00 PM   #7
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Seen something similar on eBay around $330
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Old 11-22-2013, 06:53 AM   #8
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I may need to find one, if I can get just a 10% improvement I'd be happy. Nice report Rick!
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Old 11-22-2013, 07:37 AM   #9
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If we could show the mfgs. a way to get "Just 10%" better economy they would make us an instant millionaire....

But here is a link to an article that claims that over 10% is possible with aerodynamic devices if you want to spend the money. The values are all in metric, but the % savings is easy to figure, as well as seeing that the ROI, at their fuel prices, only took a little over 100,000 miles, easy to do for the average FGRV owner ...Right...

Wind deflectors: do they really work?

Note that this is a single, somewhat non-scientific study, in which the driver(s) may have had a vested interest in the outcome.

IMHO: Adding an Ultragauge, such as Norm and others use, to monitor your driving habits, will result in a much quicker payback. <$100
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Old 11-22-2013, 07:56 AM   #10
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Name: Eddie
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Nice job. This is the second first had report of great results with a wind deflector. With a 5er keeping the bugs off the nose of the trailer is worth the effort to use one alone.
Eddie
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Old 11-22-2013, 08:07 AM   #11
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That was more than just a wind deflector. It includes a full aero kit for the TV and the trailer. Everything that is green was added. While keeping bugs off is a benefit, the cost still seems a bit high for RV use.
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Old 11-22-2013, 10:03 AM   #12
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Well, sounds like a Geek Project for the winter.
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Old 11-22-2013, 11:29 AM   #13
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Rick, that is great that it made such a good improvement.
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Old 11-22-2013, 01:34 PM   #14
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How did you go about finding the optimum angle?
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