see i dunno cause i havent seen it done yet..usually people only have an inch difference between front and back, remember seeing a S14 with 18s and 19s and it looked shit hot, same goes for 17s-18s on skylines.. i see alot of the street machine crowd do 18s and 20s (or 20s and 22s) and it can look really tuff, but yeah, thats a different style of car..Yet to see it on a skyline..I think the main thing really is to have the tyre sidewalls close to the same size so everything looks in proportion..