If you keep the same overall tire height it shouldn't effect anything.
P.s - if you decide to get rid of your 18's I may know someone interested :-)
2013 Oxford White ST3
2012 Sonic Blue Hatch ---> Sold
|FSwerks Stealth Catback||Steeda Cold Air Intake|
2003 Dark Shadow Grey ZX3 ---> Sold
2000 Silver Frost ZX3 ---> Totaled