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rallye bob · 06-19-2010, 08:07 AM

Some info I have read on this subject................
You will never recoup your investment ... AND.....

Believe it or not, those rooftop wind deflectors on pickup trucks could actually DE-crease your gas mileage.

Yes. I said it could DE-crease your mileage.
The reason is because the top edge of the pickup truck model deflector does not extend above or even reach the top edge of the trailer's roof line and the deflector sits too far forward of the trailer's front.

Thus the wind "slips" over the top edge of the deflector, goes down behind the deflector and then pushes against the front of the trailer.

This causes increased drag, as if the trailer had suddenly gained several hundred pounds of extra weight.

For a deflector to work, two things are a must:

#1. The deflector's top edge must be at least even with the top edge of the trailer and if the deflector's top edge is a few inches above the trailer's roof... all the better..

#2. The deflector must be located within six to twelve inches of the face of the trailer...

The pickup truck models are normally mounted on the cab of the pickup truck which is several feet away from the front of the trailer....

This once again allows the "Slip-Stream" of air to fall down behind the deflector and then push against the front of the trailer.

There was an in depth write-up in one of the RV magazines a few years ago on this subject.

Take a look at a big tractor-trailer rig going down the road....

The newer style trucks have the air foil designed as part of the truck cab and is taller than the trailer roof and wider than the trailer sides and it is configured so that as the trailer rotates on its 5th wheel pin, the edges of the trailer clear the air foil without hitting it.

And the older trucks use either a "Wide" or a "High" deflector so that the slip-stream will either go around the sides or go over the top of the trailers..

Do yourself a favor and spend that money on things that will make your RV experience more enjoyable...

Several cases of cold beer come to mind ..
Some "Food for thought"....

06-19-2010, 08:07 AM	#2
rallye bob Member Join Date: Sep 2006 Location: Genoa, Illinois Posts: 489 Likes: 9 Liked 6 Times in 4 Posts	Re: WTB Roof Air deflector Some info I have read on this subject................ You will never recoup your investment ... AND..... Believe it or not, those rooftop wind deflectors on pickup trucks could actually DE-crease your gas mileage. Yes. I said it could DE-crease your mileage. The reason is because the top edge of the pickup truck model deflector does not extend above or even reach the top edge of the trailer's roof line and the deflector sits too far forward of the trailer's front. Thus the wind "slips" over the top edge of the deflector, goes down behind the deflector and then pushes against the front of the trailer. This causes increased drag, as if the trailer had suddenly gained several hundred pounds of extra weight. For a deflector to work, two things are a must: #1. The deflector's top edge must be at least even with the top edge of the trailer and if the deflector's top edge is a few inches above the trailer's roof... all the better.. #2. The deflector must be located within six to twelve inches of the face of the trailer... The pickup truck models are normally mounted on the cab of the pickup truck which is several feet away from the front of the trailer.... This once again allows the "Slip-Stream" of air to fall down behind the deflector and then push against the front of the trailer. There was an in depth write-up in one of the RV magazines a few years ago on this subject. Take a look at a big tractor-trailer rig going down the road.... The newer style trucks have the air foil designed as part of the truck cab and is taller than the trailer roof and wider than the trailer sides and it is configured so that as the trailer rotates on its 5th wheel pin, the edges of the trailer clear the air foil without hitting it. And the older trucks use either a "Wide" or a "High" deflector so that the slip-stream will either go around the sides or go over the top of the trailers.. Do yourself a favor and spend that money on things that will make your RV experience more enjoyable... Several cases of cold beer come to mind .. Some "Food for thought"....