The run groups for the Autocrosses are not really "performance" based. Generally, the Red and White run groups tend to have more experienced drivers and instructors, because we use those groups for timed run corner working. This has led to the perception that the Red run group is the "fast" group
, and many/most of the TTOD (Top Time of Day) cars are in that group. However, I believe some of the TTODs at last weekend's AX were in the White and Orange groups.
In order to make instructor-student pairing easier, we put instructors in the Red, White, and Orange groups, with their students in the Blue, Green, and Yellow groups (respectively).
If you are are not an instructor or a student (i.e., you are a "solo" driver), you could wind up in almost any group, but will probably be assigned to Blue, Green, Yellow, or Orange, rather than Red or White.
The tire speed rating has no effect on AX ratings or acceptability (although we discourage the use of snow chains and studs, as they do tend to tear up the track
). The use of an R-compound or C-compound tire or any race tire (e.g., slicks or non-DOT legal tires) will add points and will force you out of an SS class. Also, any tire with a wear rating of 200 or less will add points and may move you out of your class.
Tires might change your class, but would have no effect on your run group selection. You can also request any specific run group, as Bob notes - but you may not get the requested group, if we need to balance the number of entrants in each group.
The full rules for Zone 8 competition are at
http://www.pca.org/zone8/rules/2004Z8DrivingRules.htm.