Tire size help

18" is probably too big for most people.... There will be practically no sidewall left.

You are looking for tire diamters that are 25.6" overall. It too late for calculating in my head but I guess you'll need a tire up front like 245/40/18 and 275/35/18 out back. That is an extremely large rim!

As long as the wheels have the proper offset, those size tires should fit. The bigger issue is the weight of that wheel/tire package compared to stock 15 or 16" combos. The 18" combos are MUCH heavier -- which will negatively impact acceleration and braking. And without an upgrade to springs/shocks handling will likely be hurt as well.

It's fine as long as you realize it's probably gonna just be a cosmetic upgrade that will likely hurt your overall performance level.