There are five categories of car classes -

• Street
• Prepared
• Improved
• Modified
• Other

There is also a driver category for Novices, and a separate class for Women.

The Stock category contains cars as normally delivered to the United States public through authorized sales outlets of the manufacturer with no modifications Any change will cause the car to be classified under "Prepared." This category will contain classifications of cars which are based on related performance potential. (See 2-2. Classes for definition.) "R" compound DOT, shaved high-performance, recaps and race tires are not allowed.

The Prepared category contains cars that may have "free" modifications and / or a minimal amount of "handicapped" modifications; "R" compound DOT tires are allowed; recaps and race tires are not allowed.

The Improved category contained cars with performance-affecting changes from standard (stock) specification, whether changed by the factory, dealer, or owner. These modifications have defined limits. All Improved cars regardless of base class will compete together.

The Modified category contains factory-built race cars and cars that have performance-affecting modifications outside the limits of the Improved category. All Modified cars regardless of base class will compete together.