**Direct copy from tuners**
The data below is for 2g's only. Sorry 1g guys. Someone else will have to step up to the plate with that.
The maximum tire tread width that will tuck under the fender is 255mm. There is physically only a few millimeters more than 255 between the knuckle and the fender (rolled) so nothing larger than that would tuck without major modification. Anything 245 and under, on the right offset wheel, will fit without much trouble.
Below is a matrix with several tire widths and aspect ratios in wheel diameters of 16, 17, 18, and 19 inches and several common wheel offsets. In case it isn't obvious from the data, wheel diameter doesn't really matter much. It's the tread width and overall tire diameter that determine whether or not the tires will fit. +40mm offset is the sweet spot. It places the tire very near the center of the available space. This becomes more and more important as width and/or height is increased over stock tire size. It is assumed that only a reasonable amount of lowering (up to 1.5 inches) will exist.
The data below is for reference only. Your mileage may vary. Void where prohibited, etc, etc. Some of the tire sizes listed may not actually exist. When the listed clearance is less than 5mm, actual fit may be determined by the specifications or tolerances of the tire brand. Two millimeters of clearance for one tire might be zero for another. If you don't like to gamble, I would recommend staying with wheel/tire combinations in the green zone.
K = Knuckle clearance
F = Fender clearance