[6] That team had but one rider, Joe Petrali, who had swept every AMA national title in 1935, due in large part to lack of competition, as well as his talent.

[6]: 7 [7] With declining AMA rider membership, the two major factories, Harley-Davidson and Indian Motocycle Manufacturing Company, were left with greater influence over the organization, which they used to establish a uniform racing class with a low barrier to entry.

[3] From the time Class C was established in 1938 until the 1953 KR, Harley-Davidson relied on the 27 hp (20 kW) WLDR, sold with lights, fenders and other equipment, intended to be ridden to the track by amateur racers, prepared by the rider and raced,[3][8] and the race-only 1941-52 35 hp (26 kW) Harley-Davidson WR which was the direct ancestor of the KR.

[9][3] Technology found on the European imports, including a hydraulic fork front suspension, a rear swingarm, four-speed transmission, unit construction, and a hand, rather than foot, clutch control, were used on the new K and KR.

[9] Indian chose to meet their competitors on their terms, imitating the OHV parallel-twin design favored by the British imports, but technical hurdles proved too great for the new engine to save the company from its demise by 1953.