you can probably get away with 215/40/18's as long as you keep your offset at 45-43mm. a lot of guys use 40mm and that's just too freakin' sticking out from the front fender for my taste. even with 45mm offset 215/45/17's i think the front tire is too far outward. but hey, i can always pop on a offset spacer for the rear, I guess to balance it out.
if you're planning to street race and stuff, stick with your factory wheels, lower your ride and get stickier tires.
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1998 Prelude SS - TEIN HA with upper pillows, SSR Integrals 17x7 with SP8000 (215/45), GReddy Evo catback, Iceman Comp Intake, DC Sports header, Apexi VAFC, ZEX 55 shot with bottle heater, NOS blanket, Factory Body Kit, Spoon F/R tower bars, JDM Foglamps, Carbon Fiber trim, Razo pedals &knobs, Fiamm Dual air horn
Future Mods: Lighten car, 2nd 10lbs nitrous bottle would be nice too.
2001 G20 P11 AT- TEIN NA, TRM Snipers 17x7 with Potenza RE910 (215/45), Arospeed Dual-outlet Muffler, K&N Drop-in Airfilter, WW Front Lip, Nakamichi MB75 1DIN 6CD Changer/Receiver, FIAMM Dual Air horns, Levoc Pedals, PIAA (H4 Superwhite H3 Ion Crystal, 168 SuperWhite)
2002 WRX MT- TEIN HA's with upper pillow mounts, 1000Miglia HT3 17x7 with sumitomo HTR+ 225/45/17, painted side skirts, Cusco front & rear strut bar, Whiteline rear swaybar, aluminum endlinks, Blitz NUR Catback, HKS seq. BOV, factory front lip, rear valance, Kartboy short shifter and bushings.
Future mods: dressup wheels with Potenza S03 225/45/17 tires, TurboXS UTec, maybe an uppipe.

by then, it'll be fast enough.
fiamm dual air horns.