1. 500 PREMIER: 1968 and earlier 500cc four-stroke OHV/OHC, or 750cc sidevalve machines.

2. 350 GRAND PRIX: 1968 and earlier 350cc four-stroke machines; 350cc air-cooled, single-cylinder, two-strokes with no more than five speeds; 250cc two-stroke water-cooled singles; 250cc twin-cylinder air-cooled two-strokes with no more than six speeds.

3. 250 GRAND PRIX: 1968 and earlier 250cc four-stroke machines; 250cc air-cooled two-stroke singles with a maximum of five speeds; 175cc two- stroke water-cooled singles; 175cc air-cooled, twin-cylinder, two-stroke machines with no more than six speeds.

4. 200 GRAND PRIX PLUS: This class combines a variety of engine designs and displacements, based on an index of performance.

5. FORMULA 750: Fully GP-kitted four-stroke machines up to four cylinders, manufactured as 600-750cc and built prior to December 31, 1972.

6. FORMULA 500: Two-stroke and certain four-stroke machines up to 500cc grouped on an index-of-performance basis.

7. FORMULA 250: Two-stroke air-cooled machines, including singles up to 360cc and twins up to 250cc, and certain four-strokes.

8. FORMULA 125: Machines up to 125cc.

9. FORMULA VINTAGE: Open to machines eligible for 500 Premier, Formula 750, Formula 500 and Sportsman 750.

10. CLASS C: Intended for AMA "Class C" machines up to and including those manufactured December 31, 1951, as ‘51 models. Also CLASS C HANDSHIFT, a championship class run together with, but scored separately from, Class C.

11. PRE-1940 GRAND PRIX: 1940 and earlier Grand Prix or modified street machines, including 500cc single-cylinder OHV and OHC and 750cc sidevalve machines.

12. CLASSIC SIXTIES: 1960 era and earlier (or like model) Grand Prix/Clubman 500cc four-stroke OHV and OHC machines, or 750cc sidevalve, in basically standard form. Plus 350cc OHV and OHC as a non-championship class. CLASSIC SIXTIES 650: Pre-unit 650cc and certain other machines, run with but scored separately from Classic Sixties.

13. SPORTSMAN: 1972 and earlier four-stroke, maximum three-cylinder streetbike-based machines, divided into 350cc, 500cc and 750cc classes.

14. NOVICE HISTORIC PRODUCTION: 1972 and earlier production street machines with the standard OEM frame, swingarm, forks and handlebar mounts. Engines use the original OEM bore and stroke. Classes are Lightweight (four-strokes up to 500cc, 250cc two-strokes and certain 350cc two-strokes) and Heavyweight (four-strokes up to 750cc and 350-500cc two-strokes). This class is intended for novice riders.

15. BEARS^®: Two-cylinder pushrod machines built up through 1968 and competing under Formula 750 specifications.

14. SIDECAR: 750cc four-stroke, twin-cylinder, or 500cc two-stroke, air-cooled, twin-cylinder powerplants. Rules available from the AHRMA national office.

15. EXHIBITION: Non-competitive exhibition or "rolling display" rides. Guidelines available from the AHRMA national office.

VINTAGE SUPERBIKE
See Section 10

1. Heavyweight: Unlimited displacement twins and pushrod triples, and displacement-limited fours and sixes built up through the 1982 model year.

2. Middleweight: Unlimited displacement singles, with limited pushrod twins, OHC twins, pushrod triples and OHC fours built up through the 1982 model year.

3. Lightweight: 1983 model and earlier singles, twins and multis using performance indexes for smaller bikes.

BATTLE OF TWINS^®
See Section 10

1. BOT FORMULA 3: Pushrod OHV machines to 1000cc, OHC 2- or 3-valve to 800cc, OHC liquid-cooled 4-valve to 650cc. Pushrod OHV machines over 900cc must run under Supersport specifications.

2. BOT FORMULA 2: Pushrod OHV machines to 1250cc, liquid-cooled OHC to 750cc, air-cooled 2-valve OHC to 1000cc and air-cooled 4-valve to 1000cc.

3. BOT FORMULA 1: No displacement limits and no limitations to engine modifications, with the exception of water-cooled 4-valve twins over 900cc.

4. OPEN TWO-STROKE: Air-cooled two-stroke motorcycles to 500cc; water-cooled two-strokes with tubular frame to 400cc; and modern 250cc GP type machines.

5. TRIUMPH THRUXTON CUP CHALLENGE: A spec class sponsored by Triumph Motorcycles (America) Ltd. for the Triumph Thruxton 900. For rules, visit www.ahrma.org or contact the AHRMA office.

SOUND OF SINGLES^®
See Section 10

1. SUPERMONO™2: Four-stroke motorcycles with more than two valves up to 510cc and two-valve four-strokes to 610cc.

2. SUPERMONO™: Unlimited displacement four-strokes.

3. SOS TWO-STROKE: Two-stroke singles to 550cc.

4. MOTARD. Motocross, off-road, dual-sport and motard-specific four-stroke single-cylinder machines of unlimited displacement (replaces Production Singles).

SOUND OF THUNDER^®
See Section 10

1. SOUND OF THUNDER^®: Unlimited displacement four-stroke singles and twins; three-cylinder machines to 1000cc; and twin-rotor rotary engines.

VINTAGE MOTOCROSS
See Section 11

1. PREMIER LIGHTWEIGHT: Certain pre-modern-era machines up to 250cc.

2. PREMIER 500: Pre-1965-era machines up to 500cc.

3. PREMIER OPEN TWINS: Pre-1965-era twin-cylinder machines 600cc and larger.

4. CLASSIC 125: 125cc two-strokes and four-strokes up to 150cc, manufactured through December 1971 and any like machines.

5. CLASSIC 250: Specific 250cc and smaller two-stroke machines introduced just after the Premier Lightweight era, as well as the heavy 350cc non-unit motorcycles.

6. CLASSIC 500: Specific motorcycles introduced just after the Premier 500 era.

7. SPORTSMAN: 125cc, 250cc and 500cc classes for machines up to model year 1974.

8. SPORTSMAN OPEN TWINS: Twin-cylinder machines up to model year 1974.

9. Open Age: Any AHRMA-eligible rider on any AHRMA-eligible vintage machine.

10. +40: Riders over 40 years of age on any AHRMA-eligible vintage machine.

11. +50: Riders over 50 years of age on any AHRMA-eligible vintage machine.

12. +60: Riders over 60 years of age on any AHRMA-eligible vintage machine.

13. +70: Riders over 70 years of age on any AHRMA-eligible vintage machine.

14. WOMEN: Riding any AHRMA-eligible vintage machine.

POST-VINTAGE MOTOCROSS
See Section 12

1. Historic 125: Certain 125cc and smaller motorcycles built up to and including the 1977 model year as the first-generation of long-travel machines.

2. Historic 250: Certain 126-250cc motorcycles built up to and including the 1977 model year as the first-generation of long-travel machines.

3. Historic 500: Certain 325-460cc two-strokes and four-strokes up to 636cc built up to and including the 1977 model year as the first-generation of long-travel machines.

4. Historic Four-Stroke: Certain four-stroke machines built up to and including the 1978 model year with up to 636cc. Overhead cam machines are limited to 500cc

5. Gran Prix 125: Certain post-1977 motorcycles up to 125cc.

6. Gran Prix 250: Certain post-1977 motorcycles 126-250cc.

7. Gran Prix 500: Certain post-1977 motorcycles 325-500cc two-stroke and up to 580cc four-stroke.

8. Gran Prix Four-Stroke: Certain 185cc-580cc four-stroke motorcycles that came just after the Historic Four-Stroke period.

9. Ultima 125: Certain motorcycles up to 125cc that do not have disc brakes or power-valve type mechanism built directly into the engine.

10. Ultima 250: Certain 126-250cc motorcycles that do not have disc brakes or power-valve type mechanism built directly into the engine.

11. Ultima 500: Certain 325-580cc motorcycles that do not have disc brakes or power-valve type mechanism built directly into the engine.

12. Ultima Four-Stroke: Certain 200cc-580cc four-stroke motorcycles that were produced either with a single-shock rear suspension or a newer engine technology.

13. Open Age: Any AHRMA-eligible rider on any eligible machine.

14. +40: Riders over age 40 on any eligible machine.

15. +50: Riders over age 50 on any eligible machine.

16. +60: Riders over 60 years of age on any eligible machine.

17. Women: Female riders on any eligible machine.

OBSERVED TRIALS
See Section 13

1. PREMIER HEAVYWEIGHT: Pre-1965 era machines 350cc and larger.

2. PREMIER LIGHTWEIGHT: Pre-1965 era machines up to 250cc.

3. RIGID: Any non-swingarm machine.

4. GIRDER FORK: Any rigid-frame, girder-fork machine.

5. MODERN CLASSIC: Any unit-construction machine up to model year 1979.

6. CLASSIC: British kit-framed two-strokes up to model year 1974 with 175cc or smaller OEM engine, and Spanish 4- speeds to 250cc in original OEM frame.

7. BEGINNER: A non-championship class for beginning trials riders on any motorcycle eligible for AHRMA trials.

DIRT TRACK
See Section 14

1. DINOSAUR: 1951 and earlier 500cc OHV and 750cc sidevalve. 

2. CLASSIC: 1967 and earlier machines; the two classes include 0-250cc, and 500cc OHV/ 750cc sidevalve.

3. SPORTSMAN: 1974 and earlier dirt trackers, divided into classes for 0-250cc, 251-600cc and 601-750cc machines.

4. SEVENTIES SINGLES: Post-vintage-era 500cc and smaller four-stroke machines such as competed in the late 1970s.

5. SEVENTIES TWO-STROKE: 1981 and earlier air-cooled two-strokes up to 250cc.

6. SENIOR: Riders over 50 years of age on any Sportsman-eligible machine.

7. SUPER SENIOR: Riders over 60 years of age on any Sportsman-eligible machine.

8. NOVICE: A non-championship class run at selected events for entry-level riders on Sportsman-eligible machines.

TT
See Section 14

1. DINOSAUR: 1951 and earlier machines, no limits on engine displacement.

2. CLASSIC: 1967 and earlier machines; the two classes include 0-250cc, and Open.

3. SPORTSMAN: 1974 and earlier dirt-trackers, divided into classes for 0-250cc, 300-600cc and 601-750cc.

4. SEVENTIES SINGLES: Post-vintage-era 500cc and smaller four-stroke machines such as competed in the late 1970s.

5. SEVENTIES TWO-STROKE: 1981 and earlier air-cooled two-strokes up to 250cc.

6. SENIOR: Riders over 50 years of age on any Sportsman-eligible machine.

7. SUPER SENIOR: Riders over 60 years of age on any Sportsman-eligible machine.

8. NOVICE: A non-championship class run at selected events for entry-level riders on Sportsman-eligible machine.

CROSS COUNTRY
See Section 15

1. SPORTSMAN, 88-200cc & 201cc-Open: Novice, Intermediate & Expert.

2. CLASSIC: Novice, Intermediate & Expert.

3. PREMIER: Novice, Intermediate & Expert.

4.+50: Novice, Intermediate & Expert.

5. +60: Novice, Intermediate & Expert.

6. +70: Novice, Intermediate & Expert.

7. HISTORIC: 88-200cc &201cc-Open—Historic-class machines; Novice, Intermediate & Expert.

8. POST-VINTAGE: 88-200cc & 201cc-Open—Grand Prix and Ultima-class machines; Novice, Intermediate & Expert.

9. POST-VINTAGE +50: Novice, Intermediate & Expert.

10. POST-VINTAGE +60: Novice, Intermediate & Expert.

11. POST-VINTAGE +70: Novice, Intermediate  & Expert.

(Also see Vintage and Post-Vintage MX class descriptions.)