I only have time to post this now, but before my NY trip last weekend I managed to cobble together some smooth wheel covers for the rear wheels of my Lancer. I wanted to do all 4 wheels, but ran out of time.
Anyways, coroplast and velcro FTW! I didn't want do any drilling or other fancy attachment methods since I have aluminum rims and I also wanted something easily removable. I've had the velcro idea in my head for a while but was worried whether that would actually hold up, especially in case of heavy rain.
After finding some water resistant velcro at Home Depot, I decided to go for it and am quite pleased with the results! I haven't had to deal with very heavy rain yet, but, so far, they're rock solid for over 500 miles and have had to deal with speeds of up to 85 mph and light rain.
<Update: I can now also report that they've held up for over 100 miles in medium to heavy rain.>
I haven't done any specific testing yet, but on my regular route I see about an 1.5 - 2 mpg improvement with just the rear wheels. I wasn't expecting quite as much! As soon as I have the time I will do the front wheels as well to see how much that adds.
I'm using six 2" pieces of velcro per cover (one in the center and one on each spoke). The coroplast isn't quite flush with the edge of the rim and is sticking about 1/16" out. Because of that, once I do the front wheels, I'll also cut holes in the coroplast (that I can just slap a piece of tape over) to be able to get to the valve stem and then tape the edges of the coroplast to then rim. That way they'll be absolutely smooth, and no water will get in from that side of the wheel. (I use water resistant gaffer tape that is super thin and so far holding up amazingly well on my grill block and over the 'rain gutters' on my windshield.)
