Cool app I found for checking different tire and rim sizes and offsets.
Just plug in what you have, say 165/80-15, IIRC 5.5 inch ET40, then in the next box what you want to try on.
Tells you the difference not only in size but what it will do to your speedo, etc
I know this subject gets asked a lot, this should help many peeps.
http://www.willtheyfit.com
If the size I posted for the stock 165 is correct, a 17x7 rim ET40 w/ 205/50-17 tire runs dead center of the stock tire but is 3/4" wider each side. The 17" would be a hair shorter.