SCCA Solo Classing Guide
SCCA Solo (autocross) classes your car based on its performance potential, as defined by a combination of stock specifications and allowed modifications. The goal is to group similarly capable cars together so competition is meaningful. Understanding the class system is essential before you spend money on any modifications — an upgrade that moves you into a more competitive class may hurt your results even if it makes the car faster.
SCCA publishes the Solo Rules annually. Classes, car listings, and allowed modifications change year to year. The authoritative source is always the current SCCA Solo Rules PDF available on the SCCA website — not what someone told you at a club meeting.
The Major Class Categories
| Category | Modification Level | Tire Rule | Examples |
|---|---|---|---|
| Street (SS–HS, GS) | Near-stock | 200TW min | GS, HS, BS, CS, DS, ES, AS, SS |
| Street Touring (STR–STF) | Coilovers, bigger wheels | 200TW min | STR, STX, STH, STS, STF |
| Street Modified (SM, SMF) | Engine, aero, wider tires | No R-comp | SM, SMF |
| Street Prepared (STS–ESP) | Significant prep | No R-comp | CSP, BSP, ASP, ESP |
| Prepared (CP–EP, DP, FP) | Heavily prepped | Open | CP, DP, EP, FP, GP, HP |
| Modified (AM–FM) | Essentially unlimited | Open | AM, BM, CM, DM, EM, FM |
| CAM (Classic American Muscle) | Domestic V8 muscle cars | Limited | CAM-C, CAM-T, CAM-S |
Street Class — The Starting Point
Street class is where most drivers start. The car must remain essentially stock — no coilovers, no significant engine modifications, no aero. Modifications are limited to things like alignment, tires (200TW minimum), and brake pads.
Street classes are designated by a letter that reflects performance potential: SS (Super Street) at the top, HS (Hatch Street) at the bottom, with GS (G Street) as the general-purpose catchall for cars that don't fit elsewhere. New cars often get placed in GS by default until a specific class is carved out.
Street Touring — The Sweet Spot for Enthusiasts
Street Touring classes allow meaningful modifications while keeping the car legal for street use:
- Coilovers and springs with free spring rates
- Larger wheels within sub-class width limits
- Upgraded brakes (same OEM mounting points)
- Limited engine modifications (varies by sub-class)
- 200TW tire minimum (same as Street)
Many drivers who have owned their car for a year or more find Street Touring to be the most competitive and enjoyable class — you can build the car incrementally and the competition within sub-classes is fierce at the regional and national level.
Choosing Your Street Touring Sub-Class
| Class | Drive Type | Typical Cars | Notes |
|---|---|---|---|
| STR | RWD roadster | Miata, S2000, Z4, 124 Spider | Most competitive class nationally |
| STX | Any | GR86/BRZ, WRX, GTI, Civic Type R | Broadest car diversity in ST |
| STH | FWD/AWD hatch | Civic Si, Focus ST/RS, Golf R | Hot hatch class |
| STS | RWD | Classic Miata NA/NB, older Civic | Slower, older cars — smaller tire sizes |
| STF | FWD | Light FWD under 2500 lbs | Niche class, fewer competitors |
PAX / Index — Competing Across Classes
PAX (Performance Adjusted Index) is a handicap system that allows cross-class comparison. Each class is assigned a PAX index (e.g., STR = 0.826, SS = 0.850) — your raw time is multiplied by the index to produce a PAX-adjusted time. Lower PAX classes have lower indexes because they have lower-performing cars.
PAX allows the overall winner of an event to be determined regardless of class — the driver with the lowest adjusted time wins overall. Most local events award a PAX trophy alongside class trophies.
How to Find Your Car's Class
- Download the current SCCA Solo Rules document from the SCCA website
- Look up your car in the Car List appendix — it will list the eligible class(es)
- Read the rules for each eligible class to understand the modification allowances
- Choose the class that fits your current modification level (you can always move up later)
- If your car isn't listed, it goes in the catch-all class (typically GS for Street, STX for Street Touring)
If you install a modification not allowed by your class, you're no longer legally in that class. At competitive events, this can result in a protest and disqualification. Know what your class allows before you spend money on parts.