So I'm probably going to get shot for the following question ( I have tried to search but failed)

I have an 05 wrx wagon and its time for new rubber but I'm thinking I might just go all out and upgrade the rims whilst I'm at it.

My problem starts when trying to find out what offsets I can actually fit on my wagon ,,, I'm looking at an 18x8 wheel and want the stance to be a little more aggressive without having to do major fender work

Any advise would be greatly appreciated or even a link to the appropriate page for the wagon owners .