Rooftop air deflectors are only a part of an overall package. If you look at the commercial fleet you'll find rooftop deflectors being used in conjunction with under trailer airflow systems and trailer rear wall airfoils. All three, when used together improve overall aerodynamics. When used alone, each part of the system offers only some improvement.
From the reports I've read, it looks like using a tow vehicle roof air deflector can, in some situations, improve fuel mileage a bit. How much? For most people, not enough to pay for the lost time installing, adjusting and maintaining the system.
The reason it works in the commercial fleet is the "millions of miles" that it's used when compared to the overall cost to use it. When you install it and drive 500K miles before taking it off, the cost is different than when you install it and drive 100 miles, then take it off until next weekend.
For most, it's a "gimmick" that looks good, has good intentions, but just doesn't pan out in actual use. Most wind up in the spring garage sale or in the dumpster when a strap breaks and the replacement costs more than just leaving it home this trip......
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John
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS
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