You kind of have two choices, either A Street Prepared (ASP), which would run in class S locally but has a brutally fast index as the Street Prepared rules allow DOT race compound tires of any size you can fit, or a better choice with more local competition would be XS-B, or XB locally. XB is essentially anything that is street legal, registered, and insured that weighs between 2150 and 2749 pounds for a rear wheel drive car. XA is 2750 pounds or more for rear wheel drive. Locally, there is one Lotus Elise, one Lotus Exige, and a handful of Miatas running XB. Tires are limited to 200 treadwear ratings. There are other rules, but very few, and if you can actually street drive the car you are likely to be legal.
Matt Leicester
