Harley-Davidson introduced the middleweight "Model K" in 1952, along with the 'KR' series of 'competition class' road-racing or flat-track racers. The KR's "Milwaukee racing iron" engine was a 744cc side-valve flathead V-twin that produced around 30 horsepower. The K had a three-speed gearbox and limited power, but the KR with its 4-speed transmission was capable of a top speed of around 80 mph.
Built as a replacement for Harley-Davidson's aging WR racing line, the KR would be a dominant force in dirt track and road-racing competition for almost 17 years. The KR took nearly every AMA Grand National Championship from 1954 to 1962.
By the late 1960s, the KRTT was capable of a 150 mph top speed, with around 50 bhp. From 1953 to 1969, the KR and KRTT delivered 13 victories at Daytona, making it one of the company's most successful road racing bikes. As the British competition started to gain an unbeatable foothold in the late 60s, HD decided to discontinue the KRTT in 1969. The final year for the street Model K was in 1956, with the 54-cubic-inch (883cc) KHK.
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