[LAP1DOUG]

If you haven't done any camber modifications, then you can run close to a "square" set-up front to rear to reduce the understeer tendency.

On Cayman rims, which are 18" x 8" front / 18" x 9" rear, I would run something like a 245 front / 265 rear combo. Dunlop ZII, Goodrich Rival, Bridgestone RE-11a, Hankook RS-3 are all good choices that can be driven on the street if the temperature is above 40F or so. NT-01's are good and very friendly track tire, but probably not much if any better than these 140- 200 treadwear "Extreme Summer" tires.

If you have optimized the front camber with camber plates or GT3 control arms then it is a different story: you need front to rear stagger to take care of the major difference in front to rear loading. Something like a 245 front / 285 rear is appropriate with the proper size wheels.

As 'Stone suggested, you need to do some research on tirerack.com. Pay attention to the following:

1- Each tire has a recommended wheel width range. You should try to stay in this range, though sometimes it can be exceeded slightly (1/2" or so).

2- In general, the tread width should not exceed the wheel width by more than 1/2" to maybe 1" depending on the application.

3- For PASM equipped cars (your 2008 could be one), the front to rear diameter should be similar to stock, which puts the rear at about 1/2" larger diameter than the front from what I recall. Otherwise, it can fool the computer. look around over at Planet-9 for advice on this. Otherwse, I like running the same OD front and rear.

4- Pay attention to gearing changes with tire diameter. A smaller tire OD will improve acceleration off turns, but may max out revs at other places on course.

5- For optimum performance, in selecting tires, you need to predict what temperature range you will be running in. Even for "street" tires, there is a huge operating range difference between an RS-3 (loves 90+ F ambient), and a Rival (rather have 70 F ambient). Study Tire Rack data, cruise the SCCA forums, and choose your weapon wisely.