American Flat Track

American Flat Track (AFT), originally the AMA Grand National Championship, is the premier professional flat track motorcycle racing series in the United States, sanctioned by the American Motorcyclist Association and operated by AMA Pro Racing. From its post‑war origins on the Springfield Mile to today’s multi‑class national series, it has featured iconic rivalries between Harley‑Davidson, Indian, key British brands, and later Japanese and European manufacturers.

AFT today runs three main championship classes—AFT SuperTwins, AFT Singles, and AFT Production Twins—across four distinct types of dirt track: Mile, Half‑Mile, Short Track, and TT Steeplechase. These classes are governed by a detailed AMA Pro Racing rulebook that defines technical specifications, eligibility, safety, and race procedures.

Series History and Structure

The series evolved from AMA “Class C” racing, created in 1933 to use street‑legal machines instead of expensive prototypes and first won by Woodsie Castonguay on an Indian in 1935. From 1946 to 1953, the AMA Grand National Champion was decided by a single event held on the Springfield Mile in Illinois, with side‑valve engines limited to 750 cc and overhead‑valve engines to 500 cc.

In 1954 the AMA introduced the Grand National Championship series, combining five event types (Mile, Half‑Mile, Short Track, TT Steeplechase, and Road Race) into a single points‑based national title. Harley‑Davidson dominated the 1950s and early 1960s through riders like Joe Leonard and Carroll Resweber, before British manufacturers BSA and Triumph collected titles with Dick Mann, Gary Nixon, and Gene Romero.

By the early 1970s, Japanese manufacturers entered strongly: Kenny Roberts won the first Grand National title for Yamaha in 1973 and repeated in 1974. From 1975, tobacco sponsorship from R.J. Reynolds rebranded the series as the Camel Pro Series (and briefly the Winston Pro Series), boosting crowd sizes and media exposure. In 1986, the AMA split road racing into its own series (now AMA Superbike), making the Grand National Championship a dirt‑track‑only championship.

Regulations continued to change to keep racing competitive and affordable: two‑stroke engines were banned from dirt track in 1987, displacement rules were refined, and new support classes were added to attract younger riders and allow the use of more readily available production machinery. In 2017, AMA Pro Racing rebranded the series as American Flat Track, introduced the AFT SuperTwins, AFT Singles, and AFT Production Twins class names, launched a new logo and race format, and signed national TV deals.

Track Types and Event Formats

American Flat Track competition is built around four event formats:

• The Mile: Raced on a one‑mile oval dirt course, often at horse racing venues during their off‑season, featuring repeated drafting and lead changes at speeds over 140 mph on twin‑cylinder machines such as the Indian FTR750 and Harley‑Davidson XG750R.

• The Half‑Mile: Similar to the Mile but on a shorter oval (approx. 0.5 miles), often at venues that also host World of Outlaws sprint cars; layouts and dirt composition vary by track.

• Short Track: Raced on approximately quarter‑mile ovals, sometimes indoors, favoring lighter, more agile motorcycles based heavily on motocross platforms.

• TT Steeplechase: Run on irregular dirt circuits that include at least one right‑hand turn and a jump; some modern “Super TT” rounds blend tarmac and dirt for a supermoto‑style layout while still fitting within flat track regulations.

Each event type emphasizes different skills—top speed and drafting on the miles, drive and bike stability on the half‑miles, aggression and precision on short tracks, and mixed‑surface race craft on TTs.

Current Class Structure and Technical Rules

AFT SuperTwins (Premier Class)

AFT SuperTwins is the top category and direct successor to the traditional “big bike” Grand National championship. Its key rules and performance parameters are:

• Engine: 4‑stroke twin‑cylinder only, with prior written approval (homologation) by AMA Pro Racing; includes both production‑based and racing‑only designs.

• Displacement: 649–900 cc overall, with specific caps:

  • Production engines originally under 750 cc may be bored and stroked but cannot exceed 750 cc final displacement.

  • Racing‑only engines may not exceed 750 cc, with a maximum allowable overbore of 0.045″ per cylinder; liquid‑cooled race‑only engines are capped at 750 cc with no extra overbore provision.

• Power and performance: 90+ horsepower, top speed over 140 mph, 0–60 mph in under 4 seconds.

• Minimum weight: 310 lbs.

• Tires: Dunlop 19‑inch, purpose‑built flat track spec tires.

• Fuel: VP Racing Fuels C10 unleaded only.

AFT Singles

AFT Singles develops emerging talent on 450cc single‑cylinder machinery, serving as the main feeder for SuperTwins:

• Engine: 4‑stroke single‑cylinder only.

• Displacement: 251–450 cc, with all displacements absolute; no overbore allowed and engines must retain stock bore and stroke.

• Homologation: Only single‑cylinder models homologated by AMA Pro Racing can be used, and applications are only accepted from manufacturers or their official representatives.

• Power and performance: 60+ horsepower, top speed over 115 mph, 0–60 mph in under 4 seconds.

• Minimum weight: 230 lbs.

• Tires and fuel: 19‑inch Dunlop flat track tires; VP C10 unleaded fuel.

AFT Production Twins

AFT Production Twins provides a stepping stone from Singles to SuperTwins by allowing riders to gain experience on twin‑cylinder bikes without immediately confronting full factory SuperTwins programs:

• Engine: 4‑stroke twin‑cylinder mass‑production engines only, with original OEM crankcases or approved replacements.

• Displacement: 649–800 cc; production engines may have bore and stroke modified but cannot exceed 800 cc final displacement.

• Performance: Comparable to SuperTwins—90+ hp, 140+ mph, 0–60 mph under 4 seconds—with the same 310‑lb minimum weight standard.

• Tires and fuel: 19‑inch Dunlop flat track tires; VP C10 unleaded.

Sporting, Safety, and Procedural Rules

Main Event Points Scale (All Classes)

Eligibility and Licensing

• Riders must hold an appropriate AMA Pro Racing license for AFT Singles, Production Twins, or SuperTwins and meet minimum age, medical, and experience requirements defined in the annual rulebook.

• Progression typically runs from Singles to Production Twins to SuperTwins, though exceptional riders may move directly from Singles into SuperTwins under AMA Pro Racing evaluation.

Event Procedures and Flags

• Championships are decided on a points basis over the full calendar, with separate titles for SuperTwins, Production Twins, and Singles.

• From 2006–2009, separate Twins and Singles champions were crowned with no overall Grand National title; from 2010 the combined overall title returned, and in 2017 the American Flat Track brand and current class structure were introduced.

• Standard flag rules apply (green for start, yellow for caution, red for stoppage, white for final lap, checkered for finish), with specific protocols for restarts. If a race is red‑flagged early, a complete restart can be ordered; later stoppages may trigger staggered restarts based on running order at the last completed lap, after a defined delay.

• False starts, jump starts, and rough riding can result in penalties including moved grid positions, stop‑and‑go penalties, disqualification from a race, fines, or suspension under AMA Pro Racing disciplinary guidelines.

Safety Requirements

• All riders must use approved safety equipment (certified helmets, protective leathers, boots, gloves, and back protection) and pass pre‑event and post‑event technical inspections.

• Motorcycles must meet technical, safety, and sound limits set by AMA Pro Racing, and any bike failing inspection may be excluded until rectified.

• Track build and barrier systems (air fencing, hay bales, wall placement) are reviewed and must comply with current AFT safety standards before events can proceed.

AMA Grand National / American Flat Track Champions by Year