Originally Posted by Dirt Bringer
I saw a post in a separate forum where an XV owner put 20 inch rims on his XV. Now, I admit, this is kind of ridiculous, but that being said, is it possible to put 18's on the Impreza, given it has the same general driveline and engine? If the tires are the right size, would it still perform normally or would that have a strongly detrimental effect on acceleration?
Some very good information on wheel size vs performance
Though they tested on a VW, I think the same rules should apply across the board.
15" will give you better acceleration and fuel economy. 18" will get you better on the skid pad, but worse in those other areas. I'll stick with the stock 17".