Taken from section 3.1 of the Rulebook.
Common restrictions, definitions, & exclusions
All volumetric references below are to engine displacement. Displacement-based class rules apply to actual displacement, not original displacement, unless otherwise stated.
a) A GP frame is defined as any motorcycle frame that was originally sold with clip-on bars for use on closed-circuit road courses.
b) A Sportbike frame is defined as any motorcycle frame that was originally sold for street use, with DOT or equivalent equipment, that exceeds 89kg curb weight, and was sold with clip-on style bars.
c) A Motard or Supermoto frame is defined as any motorcycle frame that was originally sold with knobby tires, one-piece handlebars, and was intended for off-pavement use.
d) A Scooter is defined as any machine with a step-through frame configuration and wheels 12” in diameter or smaller.
e) “OEM” is defined as the Original Equipment Manufacturer part, or the manufacturer-specified replacement part if superseded.
f) “OEM-equivalent” is defined as any aftermarket part with the same shape, size, mass, materials, and performance as the OEM part it replaces.
g) “Unmodified” is defined as no dimensional or material changes relative to OEM. Parts may be painted, cleaned, and polished, but the material, shape, size, and function of the parts may not differ from OEM. Unmodified parts are a superset of OEM and OEM-equivalent.
h) “Stock-appearing” is defined as appearing to be the same shape and size externally as stock, but may be modified internally or of different materials. Functional external features of the part (such as cooling fins, exhaust pipe diameter, etc) must be unmodified.
i) “As delivered” is defined as how the motorcycle was available from the manufacturer.
j) “Mini”, “minibike”, and “mini moto” are defined as any motorcycle that meets or does not exceed the class limits as defined in the Open Mini class.
k) “Lightweight” is defined as any motorcycle that exceeds 275lbs or exceeds the class limits as defined in the Open Mini class, but does not exceed 450cc in displacement.
3.2.2 Restrictions for all classes
a) Only single- or multi-cylinder internal combustion engines are permitted. Outside the “Alternative power” class, electric motorcycles will be evaluated individually based on a power to weight formula.
b) Only commercially-available gasoline-based liquid fuels are permitted. Ethanol blends up to E85 are permitted. Leaded fuels are permitted.
c) Nitromethane and methanol fuels are prohibited.
d) Forced induction is prohibited.
e) External chemical power enhancement (nitrous, etc.) is prohibited.
f) Any vehicle with more than two wheels is prohibited.
g) Knobby tires are prohibited except in knobby-specific sprint classes.
h) Additional/external fuel tanks are prohibited; motorcycles must maintain the OEM number of fuel tanks in all classes.
3.1.3 Exemptions for all classes
The following are considered exempt from any rules requiring “OEM”, “unmodified”, “stock-appearing”, or “as-delivered” parts, except as specifically noted:
a) Controls (bars, levers, footpegs, rearsets, switches), bodywork, seats, windscreens
b) Tires, hoses, cables, batteries, brake pads/shoes
c) Fluids, lubricants, hydraulic/brake lines, fuel