Top Fuel (TF) - Purpose-built, Nitromethane burning, injected or supercharged V-twin dragsters up to 200 c.i.
Pro Fuel (PF) - Purpose-built, nitromethane burning, injection only V-twin dragsters up to 151 c.i.
Pro Dragster (PD) - Purpose-built, nitromethane burning, carbureted V-twin dragsters up to 122 c.i.
Modified (M) - Race or street legal V-twins up to 122 c.i.. Gas only. Weight restrictions enforced.
Pro Modified (PM) - Purpose-built, highly modified production-based engine dragsters. 9.99 E.T. or quicker. Various fuel and fuel delivery options are legal. Weight restrictions enforced.
Super Gas (SG) - V-twins of any frame configuration, heads-up, pro tree class with 9.90 second index.
V Pro (VP) – Gas burning v-twin based engines modified for drag racing. This is a heads up, .400-second, pro tree class.
V-Rod Destroyer (D) - The VRXSE Screamin' Eagle V-Rod Destroyer is Harley-Davidson's first out-of-the-box, drag racing motorcycle. This bike can do a quarter mile run in under 10 seconds. Heads up class.
Stock XL (XL) - Street stock Sportster XL 883. Heads-up class with pro tree.
Super Bike (SB) - Metric production-based engine drag bike E.T. class with various fuel and fuel delivery options.
Pro Street (PS) - Formerly Street Bike Shootout, this class is for street legal motorcycles with any engine modifications or fuel. Except nitromethane.
Street (S) - Street motorcycles with any type of fuel delivery system. Gas and nitrous oxide only.
Hot Harley (HH) - E.T. class that is reserved for street legal Harley's. Only push-rod, air-cooled, 45-degree V-Twin cylinder engines are permitted.
Super Street (SS) - All brand, mildly modified street legal motorcycles.
More detailed specs can be found by clicking on the "Rulebook" section on this site.