So I have C5 wheels. Rears are 18x9.5. I currently have 245/40/18's on em and well their not enough to have a meaty sidewall on em and because of this has caused previous bad parkers to rash off most of the lip they had on em. I got a good deal on a 275/35/18's which is gonna replace one of my worn Pirelli Pzero's.

I have a question though, From what I have seen, arent 275/40/18s what came with these wheels? I currently have 2.25' spacers on the rear and my final question is what are the biggest/widest tires that the 18x9.5's can support anyways without having to either get wider spacers or it looking weird?

Thanks,
Carlos.