OK, so if I understand you correctly, moving the tire from the roof to a tow hitch mount would make a measurable difference, particularly for highway driving (long trips at higher speeds). This is what I suspected... Now, saying that I move the tire, how much additional benefit would I get from either removing my Load Warrior rack, or possibly designing a new wind fairing? I've always wondered whether that wind fairing, which only covers the front of the rack, but leaves a large gap underneath through which a lot of air passes, could be improved if it extended all the way to contact with the roof. Would covering this gap improve the aerodynamics or create more drag? What about if the angle was greater allowing air to flow over it better, or even if the fairing were removed to allow air to pass through the rack (as it would be empty most of the time)?

Here's a pic to help visualize my setup: