Tires, what are you running...

[Parkway Ford Lincoln SVT]

Your factory width wheels are going to limit the choices you have for the type of rubber you're considering. Ideally you would get something from the "extreme performance" category which are the 180 to 200 treadwear rating street tires that are also trackable. But in 18" sizes that are tall enough for an S197, most are 275 width or larger which will require at least 9" wide wheels, 9.5 or 10" being even better. One exception is the Bridgestone RE-71R being available in 265/45R18 which could be squeezed on to your 8.5" wheels, but that's still a compromise.

[Stephen06GT]

Your factory width wheels are going to limit the choices you have for the type of rubber you're considering. Ideally you would get something from the "extreme performance" category which are the 180 to 200 treadwear rating street tires that are also trackable. But in 18" sizes that are tall enough for an S197, most are 275 width or larger which will require at least 9" wide wheels, 9.5 or 10" being even better. One exception is the Bridgestone RE-71R being available in 265/45R18 which could be squeezed on to your 8.5" wheels, but that's still a compromise.

I found the wheel size to be an issue as well. I wish I didn't like the wheels so much then I could look for a set of 18x9 or 18x9.5. What size were the wheels on the first gen S197 GT500s? If I can get a set of those cheap then I can get a set of track tires and make my existing Nitto's last one more season then get new street tires in 2019. Just thinking out loud.