Cars and vehicles are classed in Solo according to modifications and potential. Each category has a set of allowed modifications and then the cars are divided into classes by ability. After all, it wouldn’t be fair to have an Italian exotic against an economy car.
Street Category (Super Street and A Street to H Street)
Classes in the “Street” Category have the most restrictive rules which keep competitors from feeling the need to make extensive modifications to their cars. “Racing” tire compounds are not allowed and only a few parts and changes are allowed to the car beyond what it had on the showroom floor.
Street Touring® Category (Super Street Touring, Street Touring Ultra, Roadster, Xtreme, Sport, and "Hot" Hatch)
Street Touring classes are the next level up from the Street classes and although they still require true "street" tires, more bolt-on modifications are allowed to make the cars handle better and get through the course quicker.
Street Prepared Category (Super Street Prepared and A Street Prepared to F Street Prepared)
This set of classes is where the level of commitment to modifying your vehicle really starts kicking in. Tires must be DOT-approved but sticky “racing”-style competition tires (sometimes called "R-comps") are allowed. This is the first set of classes where competitors can modify some engine externals (induction, exhaust, etc.) and even swap parts between some trim levels.
Street Modified Category (Super Street Modified, Street Modified, and Street Modified Front-Wheel-Drive)
Want to add a turbo? Do an engine swap? Install a cam? A wing for some aero-grip? This set of classes might grab your interest. Tires must still be DOT-approved but R-Compounds are allowed.
Prepared Category (X Prepared and C Prepared to F Prepared)
This is a step up from the “Street” set of classes and is based off wheel-to-wheel road racing preparation for production-based cars. Prepared allows true racing slicks (non-DOT tires) and "guttting" of the interior are allowed. Rules for this category can get more intricate based on what car and class you’re running, so it pays to familiarize yourself with the rules when building a specific car for its Prepared-level class. Convertibles are required to have a bolted-on factory hardtop and/or a roll bar.
Modified Category (A-Modified to F-Modified)
The highest set of allowances, these classes have a place for cars built specifically for autocross, production-based cars with the most extreme modifications, and road racing formula cars and sports racers. If your car doesn’t have a good place before this, it is sure to find a place here.
Karts, Classic American Muscle, Xtreme Street etc.
There are some classes which don’t fit the previous sets, but play an important part of automotive and racing enthusiasts lifestyle. SCCA has classes for karts, Classic American Muscle (CAM), Vintage cars, and College-engineering Formula SAE.