The oldest and most traditional type of racing sanctioned by the AMA is flat track—sometimes referred to as dirt track”—racing. Dating back to post-World War II, flat track is the uniquely American type of motorcycle racing. Racers maneuver their machines through turns, inches from each other, at speeds over 100 mph.
Prior to 1954, the focal point of flat track racing was the Springfield Mile at the Illinois State Fairgrounds. The 25-mile race was the most prestigious event that determined the winner of the AMA National Dirt Track Championship. In 1954, the AMA established the Grand National Championship series.
Initially flat track and road racing were in the same discipline, but in 1986 the AMA decided to separate the two. In the last 10 years there has been a great push to heighten the visibility of the sport. The AMA has worked hard to acquire broadcast contracts and sponsorship. They set new equipment guidelines to bring more manufacturers and teams into dirt track racing at the Grand National level.
During 1999-2001 seasons they began testing the 1000cc engine formula rather than the traditional 750cc engines previously used. Although the SuperTracker series was discontinued in 2001, the research led to valuable insight.
Today, AMA flat track racing is divided into two distinct classes: the AMA Grand National Twins Championship held on the mile and ½ mile and the AMA Grand National Singles Championships held on the short track. These classes travel under the banner of the AMA Flat Track Championship.
Sources:
2008 AMA Flat Track Series Guide