I have 235/50/18
What pressure you all running? Is 36 too low? That's where mine are at. Trying to get this tire paint to not crack and I think they are just not aired up enough, maybe giving them too much roll. I don't know. If I would have thought I couldn't get these letters painted, I would have switched down to a 16 and got the white lettered Nascar tires.
There is a 2.32% difference in the 18's and 16's but will a 16 rim fit this 07 SS? Suppose I could always try my Moms or just get over it and go blackwall. Once you go black, you will never go back..They are easier to care for that's for sure.
Edit: I checked my tires and they are 51 PSI max, Is 36 too low, how high could I actually go??

 

You can run 16s on that car, I have a second set of 16s on my parents' 06 SS.

Air Pressure placard is in the door. I believe it is 30/32 PSI for your car.

Sidewalls are MEANT to flex, it's what prevents your tires from popping when you run over something.

To know if you are over or under-inflating you need to keep an eye on your treads. When you take the tires off to rotate them, pay attention to how they are wearing.

If the middles are going before the sides it is over-inflated, if the sides are going before the middle it is under-inflated. If one side is going, then you have an alignment/suspension issue.

 

I usually go about 32.

 

Im running 33 in mine

 

Vehicle weight divided by 100.
Keep tire pressure within +/- 4psi of this figure.
This is on the pretense your tires meet or exceed recommended load rating for your vehicle.

 

Door Placard of your vehicle specifications. The math was already done, and the testing as well.