Just for clarification. Stock rim sizes on an otherwise legal stock car ( still allows alignments, shocks, cat back exhaust ) and any DOT R compound tire (Victoracer, Hoosier Autocrosser, A302, BFG G-force R or whatever it is called now) is allowed in stock. You are allowed the same tires on any sized rim (and other mods) in Street Prepared. If you run a non-DOT tire (aka a full racing slick like Kenan runs on the yellow Mustang) then you have to run in Prepared where you are allowed to gut the interior and do lots to the internals of the engine.

Now STS, STX and SM really don't follow these guildelines and are an exception.