In the Miata community, 225 width tires work best on 9" width wheels. In the S2000 community, 255 width tires work best on 10" width wheels. The width of the tires is basically equivalent to the width of the wheel.
225/25.4 ~ 9", likewise, 255/25.4 ~ 10"
Anymore stretch than that is overkill and does not function as well as what I mentioned earlier. Most people will run whatever is recommended on the spec sheet, for example, 255 tires on 9" width wheels, 245 tires on 8.5" tires, 235 tires can be either on 8.5" or 8" wheels, etc.
For stock power, 215 width tires are good enough for the BRZ/FRS. We ran 215s on 8" width wheels to start off with on the track. This extra "stretch" helped improve some sidewall stiffness, but the car needed serious camber to fix most of our wear problems!
Autocross guys have to use the OEM wheel sizes for certain classes and will stuff as wide of a tire as possible. That's because those specific tires have super stiff sidewalls and at slower speeds, more tire equates to more grip for the given course. I'm not much of an autocross guy, so some autocross guys have to chime in on that idea.
Hope this helps out!
