Larger rims require modification?

[1GtUnV]

Got a 97 gt. Im thinking about going from 17x9 all the way aroudn to some 18x9 in front to 18x10.5 in the back. I have an Eibach spring kit but i dont think that will matter much, because its not a big drop. What problems will i run into?

 

[98blackmagic]

I'm not sure about the front but on the back the quad shocks and tail pipes could be a problem. I and getting ready to buy 17x10.5 bullets and will probally have the same issues.