So after upgrading to 20s from factory 15s, I noticed that my MPGs on my car were horribly low. With the 15s my car averaged 21.8 (22 in the city is factory rating), and now with the 20s my car is getting roughly 18.0-18.2 MPG. The thing that throws me off is I called ford and they said that it was about 100 more pounds on your car so it would affect your gas mileage by 2%. So if we take 22 x .02 = .44 decrease, which should give me 21.56. How is it that I am getting 18 MPG. Any suggestions?