What class is my car in?

This can sometimes be a tough question to answer. We have some of the most important rules below. Take a look over them, especially if you’re thinking of modifying your car, so you get a feel for what kinds of cars compete in which classes.If you can’t figure out what class to register your car in, no problem! At the registration table, the morning of an event, we can help you figure it out.

Stock – This category includes mass-produced, common vehicles that may be “daily drivers” (cars used for normal, everyday driving). Stock Category cars compete in their “factory” configuration with a minimal number of allowances (not requirements) such as:

  • Removal of spare tire and tools
  • Front anti-roll bar(s), including mounts and endlinks
  • Suspension/wheel alignment using standard adjustments
  • Factory-specified crash bolts are allowed (but no aftermarket bolts/alignment products)
  • High-performance DOT tires (including competition R-compounds)
  • Shock absorbers/struts (2 external adjustments maximum, springs may not be changed)
  • Competition-type seat belts (no shoulder belts in open cars)
  • Brake linings (pads/shoes)
  • Air filter element (the “throw-away” part)
  • “Cat”-back exhaust systems
  • Wheels of standard size (diameter, width, and offset within +/1 6mm – may use spacers)
  • Roll bar/cage
  • Gauges, indicator lights, etc. (convenience items)
  • Option package conversions are allowed as long as all components are carried over, including trim pieces, badging, etc. This ONLY includes factory option packages (i.e. 94-97 Miata R-Package) and does NOT include dealer-installed items or packages (i.e. TRD parts for Scion).

Street Touring – Started in 1997, this is one of the more popular categories which includes Street Touring (ST), Street Touring Sport (STS), Street Touring Xtra (STX), Street Touring Roadster (STR), and Street Touring Ultra (STU). This is the only category that does not allow competition R-compound tires – only high performance tires with a UTQG treadwear rating of 140 or higher.

ST consists of sedans/coupes with four seats minimum and normally aspirated engines up to 3.1L (very few turbo/supercharged cars are allowed).

  • Stock category allowances
  • No limited slip differentials except for standard viscous-types
  • Pedal kits and other interior trim
  • Front seats (25 pounds minimum weight each, including mounts)
  • Rub strips, emblems, and mud flaps removed
  • Body kits, spoilers, and wings added
  • Tires up to 225mm wide, UTQG treadwear 140 minimum
  • Wheels up to 7.5 inches wide, any diameter/offset
  • Any shocks/struts, number of damper adjustments is unlimited
  • Drilled/slotted rotors (standard size) and braided DOT brake lines
  • Anti-roll bars, front and rear, including mounts
  • Lowered suspensions using standard-type springs (commonly referred to as “coilover” suspension kits)
  • Suspension bushings (non-metallic)
  • Camber kits, plates, or bolts
  • Traction bars, torque arms, panhard rods
  • Strut bars, 2-point only
  • Battery relocated
  • Air filter systems up to throttle body or compressor inlet
  • Headers, emissions compliant
  • High-flow catalytic converters (no test pipes) – must be within 6 inches of factory location
  • Engine computers (PCM/ECU) reprogrammed
  • Shifter kits
  • Accessory drive pulleys
  • Motor mounts (non-metallic)
  • Boost controllers are NOT allowed (manual, electronic, ECU-based, or otherwise)
  • Example of included cars: Audi A4 1.8T and TT (non-quattro), Mazda 323 GT and GTX (AWD), Volkswagen Golf/GTi/Jetta/Beetle/Passat 1.8T and TDI, Volvo S40 (except T5) and V40
  • Example of excluded cars: Datsun Z 2+2, Honda CRX, MGB GT, Porsche (all), Triumph (all)

STS is for sports cars with only 2 seats and normally aspirated engines up to 1.9L.

  • ST allowances
  • Included cars: BMW Z3, Honda CRX and del Sol, Mazda Miata (1990-97) and RX-7 (1979-92) (non-turbo), Toyota
  • MR2 (1985-89) (non-supercharged)
  • Excluded cars: Lotus (all), Mazda Miata (1999+), Toyota MR2 (1991-95, 2000+)

STX is for sedans/coupes with four seats and engines up to 5.1L normallyaspirated or up to 2.0L turbo/supercharged.

  • ST allowances
  • Tires up to 245mm wide (AWD) or 265mm wide (RWD/FWD), UTQG treadwear 140 minimum
  • Wheels up to 8 inches wide (AWD) or 9 inches wide (RWD/FWD), any diameter/offset
  • Limited slip differentials allowed (any type, including aftermarket) for 2WD cars
  • Larger brake calipers and rotors, including 2-piece rotors
  • High-flow catalytic converters – may be consolidated into ONE main converter (i.e. Subaru WRX may remove two of their three converters)
  • Excluded cars: Audi S4 (V8 engine), BMW M3 (E36, E46) and M5, Mitsubishi Lancer Evolution, Subaru Impreza WRX STi

STR is for sports cars with only 2 seats and normally aspirated engines up to 3.5L

  • ST allowances
  • Tires up to 225mm wide (AWD) or 255mm wide (RWD/FWD), UTQG treadwear 140 minimum
  • Limited slip differentials allowed (any type, including aftermarket) for 2WD cars
  • Legal cars are limited to: BMW M Coupe/Roadster (98-00), BMW Z3 (non-M), BMW Z4 (non-turbo, non-M), Datsun Z car (non-turbo), Honda S2000, Mazda Miata/MX-5 (non-Mazdaspeed), Mazda RX-7 (non-turbo), Nissan 350Z, Pontiac Fiero, Pontiac Solstice (non-turbo), Porsche 911 (3.2L, 84-89), Porsche 924/944/968 (non-turbo), Toyota MR2/MR2 Spyder (non-turbo)

STU is for sedans/coupes with four seats and normally aspirated engines of any
displacement normally aspirated or turbo/supercharged engines up to 3.1L.

  • ST and STX allowances
  • No wheel restrictions
  • Tires up to 245mm wide (AWD) or 285mm wide (RWD/FWD), UTQG treadwear 140 minimum
  • Example of included cars: Audi S4, BMW M3 (E36), Chevrolet Camaro, Dodge SRT-4, Ford Mustang, Mitsubishi Lancer Evolution, Pontiac Firebird / Trans Am and GTO, Subaru Impreza WRX STi, Volvo S60 R
  • Excluded cars: BMW M5 (E39)

Refer to the SCCA National Solo Rules for full details and specifications on
the Street Touring allowances.

Street Prepared– The original SCCA “street” category, Street Prepared allows any carburetor/fuel injection system and any ignition system. Turbo/supercharger hardware has to remain standard, but aftermarket boost control systems/programs and intercoolers are allowed. Exhaust manifolds and systems are free. Emission controls are not required for competition, but no internal engine or transmission modifications are allowed beyond factory specs (no cams, hi-comp pistons, ported heads,  etc). Some cars are able to update/backdate components like engines, brakes, etc (See Solo Rules for details and specifics). There are no limits on wheels sizes or DOT tires; racing springs and shocks are the norm.

Street Modified – The top of the “street” categories, Street Modified allows anything from Stock, Street Touring, and Street Prepared and just about any engine and drivetrain configuration as long as the engine manufacturer matches the body manufacturer (see Solo Rules for details). Most four-seaters (BMW, Supra, Talon,  VW, etc.) run in SM and two-seat sports cars (Corvette, CRX, M Roadster, Miata, RX-7, MR2, etc.) compete in SSM – there is also a FWD-specific, four-seat version called SMF (Street Modified FWD). Carbonfiber hoods, cams, turbo/supercharger kits, etc are welcome, too.

Prepared – These cars are not for the street; they are virtually race-prepared vehicles for dedicated Solo® competition. Gutted interiors and racing slicks are the first visual characteristics of these cars and when they crank up, you can tell these engines weren’t built for bringing home the groceries. Convertible cars are required to install roll bars per the Solo Rules.

Modified – Except for D and E Modified, these were never ever “street” cars. They are special built competition vehicles and most of them resemble an openwheel Indy car or a closed-wheel LeMans sports racer. DM and EM cars may have started life on the streets, but just about any engine, drivetrain, or suspension is permitted. Supercharged rotary engines and V-8 engines are seen in 1700 pound EM machines and powerful 4-cylinders are common in 1300-pound DM lightweights.

For complete class preparation breakdowns, see:


(allowed modifications for each class in detail)
(class breakdown and eligible cars)

Also, a general rule-of-thumb to remember is this:
If the rules don’t specifically allow a certain modification, it is NOT allowed. (Some of the more common technicalities are outlined.)

Comments are closed.