I hate calling them "skirts", especially on an F150 - so they are covers. This construction method would work for any car though.
Made an aluminum frame out of 8' aluminum angle pieces by cutting triangles out of one edge. This allowed for it to mold to the inside of the wheel well lip and still give me a surface to attach the cover to. I did drill and screw this aluminum piece to the well lip. Next the cross braces were bent so that they would clear the tire, and were then riveted to the half-circle. A little brace piece was added for the bottom bracket - I wanted more than 2 rivets holding that on!
Next I used metroMPGs newspaper method to get an outline of my wheel well, transposed that to a piece of choroplast. Cut the choroplast, taped it in place on the wells, drilled holes for plastic rivet/screws that would hold it onto the frame. Drilled the frame holes while the paint was drying on the choroplast (4 coats - we will see how long it lasts... at least its an easy quick spray paint touch up to scratches that may occur). I put door edge around the edge of the choroplast to give it a finished look and then attached it to the framework.
I designed it this way so that I can remove it easily in 2 steps...cover first then the aluminum frame... when I need to have tires replaced. If I have a flat, the lug-nuts are all accessible when I lift the truck. Not sure if there is clearance to get a tire swapped without removing it, but hopefully Ill never find out. (of course now that I say that, Ill have a flat tomorrow).
I have another 800 mile round trip run next week - will see what kind of difference these things make - hopefully a pretty good one - those wells are huge back there.
I got 23.1 hwy tank before this change...Im really hoping to see 24-24.5 with it. Will find out next monday/tuesday. The hard part for me is not making some other change before the trip, so I know what each change does. Then again - I may get ambitious...who cares what changes makes the most impact - they all work together to give the biggest bang.
Well, I'm not so sure, but I think a lot of it has to do with the wheels, particularly how much air they suck in and all that. I know for bikes the inside of the wheels pose lots of drag, but of course that's different, I was just excited to learn it.
Another source of drag is just plain old how far the wheels stick out under the vehicle. I'm not the best person to really answer the question though.
Another user joins the wheel skirt group. Love it. The only problem I can see for you is this. When you tell certain people that you get 24hwy they'll say stuff like "I have a v6 dodge ram and I get 30mpg all the time". But of course that really isn't a problem is it.
02 Saturn SL
for pics click the link below