wheel disk covers... MPG myth or not?

[bestmapman]

I have four on my Prius, and it helps some. How much, I don't know.

[JanGeo]

I am now getting 49-52mpg at night on my Tiverton to Newport Trips (usually 48mpg) and the tank average is hunting around 45mpg for 3/4 of a tank now . . . could be a pretty good (near record high) tank of gas mileage wise IF I keep the short trips to a minimum.