[aerohead]

I tossed your numbers around on Al's calculator.30-inches of added frontal area to a car with say,20-square feet of frontal area would raise the drag by 1-%.The mpg penalty at 55-mph could not be over 0.5%.Since a jump between 35 and 37 is on the order of 5% mpg,the wheel skirts should not be able to alter the mpg to this magnitude.I think there is more going on than just the skirts.Just my guess.