Tire Sizing Questions

Hi Everyone, this is my first post here but been regularly browsing these forums for several months now. I'm currently looking for some advice selecting the right size tire for street driving and autocross. My current car is a '06 Pontiac GTO. It is pretty much stock but has coilovers with 8k/10k springsm, a handful of poly bushings, and a new intake. I am running the stock 18x8 wheels too. My current tires (235/40/18 Conti ExtremeContact DW) are getting pretty worn out and I'm looking for something new. Unfortunately at this time I can't spend the money on buying nice 9" or 10" wheels. As such, I'm looking to get the best tire setup I can get on my 18x8s.

The max recommended size by the tire manufacturers are 245/40/18. With a heavy, powerful car like mine, I feel like this would still leave me quite under-tired and would put me at a disadvantage against the STIs and Evos running in STU. I have been looking at maybe getting 255/35/18s or 265/35/18s and sticking those on. An 8" wheel does seem a bit too small though and due to clearance issues, I won't be able to run as much negative camber (maybe -1° up front). I also don't get the full potential contact patch and I'm nervous that a bulging tire will make steering inputs less responsive and mushy.

I'm also looking for input on tires for my car. The Conti ExtremeContact DW tires have been great for daily driving but they are really not up for the task of autocross (70-90 second runs) and during my last event, the tires started chunking a tiny bit. I've been reading the reviews on GRM but the tests were done on a car that weights a good 1200-1500 pounds less than mine. The Hankook RS3s seem to be the best value and my first hand experience with them is that they offer incredible dry grip. Do you think their sidewall stiffness would be adequate for my car or would I be better off going with something like the Dunlop star specs or the Bridgestone RE-11s? Also, I'm open to most alternatives with a price under ~$280 per tire. I am against getting any type of staggered setup though due to my car's inherent understeer and my desire to rotate tires at least front to back.

Thanks in advance for any suggestions you have!

245 section is the widest that you will be able to properly fit to an 8" rim. I wouldn't try to stuff wider tires on a narrow rim. Sounds like you are also running the tires on the street. That leaves out extreme R compound tires. I run the BFG Sport Comp 2 tires on my Porsche and they are killer. Excellent dry grip. Not dangerous in the rain. Decent tread wear. Pricing is very good. If you really need a larger section tire, swap your wheels. Maybe even going to 17's to get the clearance you need for the tire and camber.

I agree. I would stick with the 245/40s until you upgrade the rims.

Thanks for the suggestions. I ordered some 245/40/18s and will move up to something bigger when I purchase larger wheels.