Hard to believe, right?
Somebody posted info from a test using a brick shape. Fairing in the back was the single biggest improvement, and here is my take on why:
No matter how you smooth the flow going onto your rig, it still displaces X amount in cross section. Still 13 high and 8 wide. No way to fool that.
At the back you can "let" that air off very gently and efficiently, or let it slam shut.
If you let it slam shut the turbulence and vacuum is so great, a car can ride with almost no power input in the wake of your motorhome. IF you think about it, you could pull a smaller motorhome along behind you
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2007 Dodge Ram 3500 SRW 4x4 with 6MT
2003 TDI Beetle
2002 TDI Beetle
currently parked - 1996 Dodge 2500 Cummins Turbodiesel
Custom cab, auto, 3.55 gears