I got 225/50/16 Potenzas on my car. Most 225 size tire just require atleast a 6.5" rim width, so they fit on stock 16" GTS rims. It'd be harder to find a lower profile tire for the stock rims though, from what I saw anything lower then 50 series require a minimum 7" rim width. So unless you got aftermarket rims I think 225/50 are probably the widest you can go, but if you find any lower profile 225s, post if because I couldn't find any.