What class are you autocrossing in? With your wheel sizes, you are obviously not running in BS or STX. Beyond that, you don't have a chance anyways; so it is a moot point what tires you get. You will have to run in STU, SM or BSP and our cars are just simply too disadvantaged to run those classes competitively.

If you are serious about autocrossing, either target BS or STX. If you go the BS route, prepare to get beat up by S2000s and Boxsters this year. Next year will be better when they move up. You have to run stock size wheels in stock classes, so you will need another set of 18x8.0" wheels. Maybe get a new set of wheels for the steet and use your stock ones for racing. Since you obviously aren't a national competitive driver, don't waste your money on Hoosiers. They are the stickiest, but their tread life is horrible. Unless you are running tours and Pros for money, they aren't going to do anything for you. You will only get a couple of events on them. Because of the stagering issue, you only have 1 choice of tires: Toyo RA1's. They have them in 225/40-18 and 245/40-18's. Kumho just pulled the ECSTA 710 off the market due to design problems, so they are out. Victoracers don't even have 18" sizes and ECSTA 700's only have 1 size that will fit those wheels, leaving no ability to stagger(if you don't stagger, you may be surprised when your ABS turns off in the middle of a run).

If you go STX, you are still limited to 8.0" wide wheels; but you can change diameters. The best setup is to go 17x8.0" all the way around and run ECSTA MX 245/40-17 in the front and 245/45-17 in the rear. You are shorter so you get the benefit of a better final drive, but stagered enough that the computer doesn't notice.

04' G35 Coupe 6-sp
Diamond Graphite/Willow w/Premium