for an s13 id go with 18x9 +5 front with a 225/40/18 and 18x10.5 0 with a 265/40/18 youll be baller.

i disagree with importluv because there is a correct offset. for instance if you run a 9.5 inch wide wheel with a low 30s offset youll never clear your coilovers (if your running them) on a 240 running high offsets is pointless it just makes for shadows and clearnace problems.

check into a wheel made by axis, they are called the wde tracks. you can get them in 4 lug. they are 18x8 +20 and 18x9 +20. they will fit easy all day long no rolling or pulling. i think thats about as aggressive as your gonna get. or just buy some mustang wheels off ebay lol.