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Originally Posted by LAP1DOUG
You need to pay attention to the overall diameter of the tires before ordering. Our cars are already geared way too tall, and larger tire diameters just exacerbate this problem. I had rather give up a little width in say going from my preferred 285 to a 275 in exchange for keeping the diameter down. Unfortunately, this compromise is way too frequently required.
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In addition to the gearing, the fronts especially do not have much room and you can't fit a 245/40/18 - it is too tall and it contacts the strut perch. I bought a set of Cayman wheels with that size mounted in the fronts and it didn't fit. (987 run a taller tire than 986 so it fit on the Cayman). The stock diameters are 25.1" in the front and 25.3" in the back - you can fit bigger in the back (I test fitted a 25.9" 285/35/18 RS on a 9" wheel in the back, not ideal for gearing but it fit) but the 25.7" 245/40/18 RS3 on an 8" wheel were too tall
I think a 10" rear wheel is OK, I have heard that 11 is where you get into a lot of trouble.
I have heard that the Bridgestone RE71R is the current 200tw "cheaty" tire in Autocross - it is really more like an R-comp, sticks like the devil, wears super fast, and I have heard it heats up really fast so it is perfect for Autocross or for getting a flying lap or 2, but for a 25 minute session it gets hot quickly and slides around a lot.
The guys in my autocross group that run chumpcar like the BFGoodrich Rival - the first one, not the "S". They say they hold up well.
I personally run the RS3 and it hold up well, I typically run 20 -30 minute sessions and I have not had them fall off due to overheating. I like the RS3 because it is directional and around halfway through their life I flip them on the wheels to get more even wear.
Discount Tire Direct often runs $100 off a $400 purchase on eBay with free shipping and folks use that to stock up on the Nitto NT-01, and I think the 18" sizes qualify with 2 orders of 2 tires and they get $200 off.