16-18. Really any larger and it just starts to look stupid. I would seriously debate putting 20s on my caprice and even that has wheel wells that look right for that size, it just would be either a hit or miss. I've seen good looking 20s on them and hideous ones too. Mostly blades, which are the most retarded wheel man ever thought up. When I get the money, I'll be going to 17x8s all the way around, because they fill up the wheel wells just the right amount and still have enough sidewall to give a good ride. Now, the 15s do look good, but I'd prefer something bigger. The caprice, I'd love do a set of 18x10 rocket racing boosters gun metal grey. That would be perfect. Understated and classy at the same time. The way the tire sits in the well can be called the 3 finger rule. the gap between the tire and fender is larger than 3 fingers it's too high and just looks weird, same goes for less than 3 fingers. That's why I can't stand the 14s. They are just too small for the wheel well, it looks like the car is driving on nickels, but 245/60 15s look just right. As long as the overall diameter doesn't change much I should be able to fit a nice wide set of 17s in there no problem.