A.M.A. Grand National Championship

The American Flat Track Series, formerly known as the AMA Grand National Championship and the AMA Pro Flat Track Series, is an American motorcycle racing series. The race series, founded and sanctioned by the American Motorcyclist Association (AMA) in 1954, originally encompassed five distinct forms of competitions including; mile dirt track races, half-mile, short-track, TT steeplechase and road races. The championship was the premier motorcycle racing series in the United States from the 1950s up until the late 1970s when, supercross events held in easily accessible major league stadiums became more popular.

In 1932, the AMA sanctioned a racing class called the Class A Dirt Track championship allowing for motorcycle manufacturers to enter prototype machinery. In 1933, the AMA introduced a new class called Class C which featured street-legal motorcycles in an effort to make motorcycle racing less expensive for ordinary motorcyclists. When manufacturers cutback on racing budgets during the Great Depression, it spelled the end of Class A competition and, the Class C championship became the most important championship. In the years prior to World War II, the Class C championship helped fuel an intense rivalry between Harley-Davidson and Indian, the two major American manufacturers of the period. During the Second World War, there were no championships held between 1942 and 1945.

From 1946 to 1953, the AMA Grand National Champion was crowned based on the results of a single race, the Springfield Mile held at the Illinois State Fairgrounds Racetrack.Side-valve engines had a maximum displacement of 750cc, while overhead valve engines were limited to 500cc. In 1954, the Grand National Championship series was introduced featuring four different types of competitions: three of the competitions (Mile, Half-mile, TT) were held on dirt tracks, while the fourth was held on asphalt paved courses. With the demise of the Indian motorcycle company in 1953, the Harley-Davidson factory was left to dominate the series. Harley-Davidson rider Joe Leonard won the first Grand National Championship in 1954 and won the title two more times before moving on to a career in auto racing. Carroll Resweber became the first four-time champion, winning four consecutive championships for Harley-Davidson from 1958 to 1961. Since 1961 short-track events became part of the Championship; those races had a 250cc displacement limit. In the 1960s, British manufacturers seeking to bolster sales in the burgeoning American motorcycle market, began to compete in the championship. Dick Mann won the national title for BSA in 1963, marking the first victory for a foreign manufacturer.Triumph would win three Grand National championships in four years with Gary Nixon winning back-to-back titles in 1967 and 1968, and Gene Romero taking another title in 1970. New regulations for 1969 eliminated the displacement penalty for overhead valve engines; in dirt track events brakes were permitted for the first time. Mann would win a second crown for BSA in 1971 before the British motorcycle industry collapsed in the face of stiff technological competition from Japanese manufacturers. In 1973, Yamaha's Kenny Roberts would win the first Grand National championship for a Japanese company. Since 1973 the displacement limit for short-track events was increased to 360cc, but multi-cylinder two-stroke engines were still limited to 250cc.

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