I was looking around online to see if anyone had posted data on wheel covers that increase MPG. I found a couple things from "pizza plates" to covering the whole wheel well itself. I decided to invest in a set of moon hub (not racer/flat) caps online and see what kind of improvements I could get out of my honda.
$100 and a tank of gas later... I didn't notice any increase in MPG after the fact. I suppose the only thing I did get out of the deal is some nice, shiny rims. I've had a few people mention " VW " rims and " 50's " style. I think they give the car a unique look, so I'm not really complaining.
I use a ScanGuage II, drive easy and try to keep weight to a minimum. However, the best I've seen is 360 miles from a 12 gallon tank of gas. I estimate about 30 city/35 hwy. Being as NEW cars get the same/less mpg than I do, I'll be hanging on to my 10yr old Honda for a while longer.
It depends upon what you had on the wheels before you switched. My xB has the 9 spoke plastic mag wheel covers and they were a lot of work to keep clean. I go tthe racing disks but they are rounded not flat - my garage has a top view in it so you can see how much of a dome they have. I noticed higher mileage than usual after putting them on but I have not gone back to the old wheel covers to see the decrease again. The slightest things can affect mileage so it is hard to say exactly what really helps a lot but if it helps at all you just have to stick with it. Usually if your mileage is not very high in the first place the major factor in your mileage is the engine efficiency and a small aero improvement will not help much anyway.
Man... that's a real bummer that you paid 100 bucks for those and didn't see any real improvement.
I know it may be a little late but here's a link to some guy on EcoModder who put Wal-Mart Pizza Pans on his wheels... I'm sure your's looks way nicer http://ecomodder.com/forum/showthrea...-6-a-4368.html