Help.. Wot Wheels Can fit??

Hi
As u already probbably know i have a 1990 Corolla that currently has 15" wheels on it.. anywayz.. wot would be the biggest size i could go up to with a wide arch conversion? i was hoping for 17" or maybe 18" if im lucky? im doing the big wheel thing becuz of the increase of power im hoping to get soon (4AGE) i think thats the 1.6 GTi (correct me if im wrong) but anywayz wot size wheels please help.
Cheers
Chris

17" is the biggest i'd recommed you go with. some people have 18s but it's not generally a good idea. make sure the wheels you're getting aren't too heavy too.