The safest method is a tight fit at the front of the wheel. One important thing to remember is that the wheel moves. Another less obvious thing to remember is gas mileage in turns is amost inconsequential. A good tight fit when straight ahead will give th best safety and fit, then vent the high pressure area behind the wheel through the fender. The fender vent will also help vent high pressure air from engine compartment.
I thought about how to do front wheel pants for way to long. I kept thinking about the best hinge and the best roller and finally said the heck with both. I just riveted some scabs to the rings which I had used to close up my wheel well gaps. I did not use hinges and I did not use rollers. I only have a couple hundred miles on them. The tire just rubs on them and the fiber reinforced material from Home Depot just flexes. The verdict is still out but so far I like them. I will need another metal strip on them to hold the shape a little better. I can turn about 1/4 turn of the steering wheel before contact. There is not much noise except when turned to the stop and doing a tight turn. The bungee cord helps hold them in. They are not finished but I finally have some front skirts.
I appreciate the concern about the tire sidewalls rubbing. The tires are old and should be replaced. I intend to run them long enough to get a good estimate of the wear rate. My tires rub on the payment too and they have held up pretty well there.
just be prepared to purchase new tires on the spot.
I know that there is some scrubbing on the tires when you turn your wheels or during breaking but you aren't scrubbing with the intensity of a die grinder.
your wheels are going to be moving possibly 60+ mph when they are rubbing. this could be the equivalent of a sand paper disc against the side wall depending on the dirt or other material either on the fender flare or on the tire.
also remember that in states where they have anual inspections ( I think there are still some that don't require it) they check your tires and side walls as well. not sure what they would say about scuffed up side walls. I do like the roller idea though the skirt would have to protrude out farther to get the roller in there. you could just use a wheel instead of a roller.
good luck, and make sure that they are removable in a pinch.
*edit* another idea, and this is a whoom dinger, is you could put a housing around the tire that turned with the tire. I heard someone mention that some concept car had done this. you would mount it behind the tire like where the caliper sits which also makes it stationary when the tire is spinning but it would turn with the tire when you turn. you could shape it so that this piece would contact the fender flare instead of the tire so that you wouldn't have the rubbing. that would make for a lot of fabrication though and a lot of time spent. like I said before, this idea is really out there.
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