Quote Originally Posted by SilentMatt View Post
It's pretty harmful to fuel mileage... It's the first car I've ever had with revs over 2500 at cruising speeds. I think it has around a 3.94 diff ratio and 185/75's would effectively put it at a 3.59. Should drop the rpm down to 2900.
4 cylinder motors are naturally high revving engines. When you have an engine that makes 104hp at 6500rpm, you need to get the revs that high to push the car at 70mph.

Larger and heavier wheels and tires will cause your engine to work that much harder than stock parts to get your car up to and maintain 70mph. If anything, that will cause a decrease in gas mileage. I lifted my Jeep 3 inches and went from 28in stock tires to 32in mud tires. My gas mileage went from 18mpg to 12mpg (Thus the reason I have the Aveo).