Well, that certainly sparked informative discussion! The ability to rotate the tires is more of a "nice to have" than necessity. I have successfully run square tires on my previous cars (295s on an R35 GTR, 305s on a ZL1 1LE), but was never able to rotate the tires front to rear. Part of my decision in moving from those cars to the s2000 was to focus on seat time at a reasonable cost; the ability to run the same wheel/tire front and rear helps further reduce running costs.

I like a free/loose car on track and I understand the AP1 is there from factory but this car has a big rear wing (as mentioned above) which *should* keep it planted in the high speed stuff. In the low speed sections, oversteer is easier for me to manage than understeer and hence the decision to run the square setup on both of my previous cars. The GTR was a pig and it took a square setup + large rear bar and disconnected front bar to get that car to rotate. The ZL1 was a bit easier.. it really just needed the square setup and then I could play with the adjustable rear bar to get the feeling that I wanted. I am thinking a similar approach on the s2000 will work, but I am all ears for ideas.

Side note: I am in process of swapping out the current Tein Flex coilovers for a set of Ohlins DFVs with 800/900 lb springs. Then I'll assess what the car needs and add F/R swaybar as needed.

 

In summery with your front fitment space as the limiting factor and to run square, id say your target is going to be a 10.5" with 285/30/18. That will be least compromising on space while getting a decent width tire under the car. Given that, I hate under sizing wheels for the tire widths, but considering the somewhat limited tire options in 285 (but the shorter therefore less sidewall deflection over 17") you could feasibly run a 295/30 on that width rim as well. Getting the right offset selected will be imperative as there is no real fudge room. 10.5" +45 is where you should be based on my experience and calculations.