540Z28

Looking at starting doing some tracking and autocrossing with my C5. Wanting to put a DOT compliant track package together. Considering TSW Interlagos in 18" with 9.5 front and 10.5 rear. I see Nitto has a NT555 RII in 285 and 305. Tire and wheels sizes are compatible. Anybody run anything like this that can tell me if they hang out the fenders any. Any other suggestions in tires. Thanks in advance guys.

2MCHPWR

why not get the same size all around (a.k.a "a square setup"). easy to rotate and get longer wear. 10.5 " wheels all around fit fine with 315's (yes they fit up front). Or use 305's all around since you mentioned that size. 555RII is fine and so is toyo R888.

Solofast

First figure out what autocross class you want to run in. If the car is stock and you want to stay in an SCCA stock class you can only change the diameter up or down one inch and you need to stay with stock widths that the car came with. I realize that might make finding the right setup more difficult, but if you change widths and end up being stuck in a class like street prepared in a stock car that will take a lot of the fun out of it.

A bit of care and thought up front will likely make life a lot more fun in the long run.

If you have a C5Z then what you are doing will work fine and still be legal in stock. If your car is a base C5 then you won't be legal with the wheel package you talked about.