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The Harley-Davidson XR-750 is a racing motorcycle made by Harley-Davidson since 1970, primarily for dirt track racing, but also for road racing in the XRTT variant. The XR-750 was designed in response to a 1969 change in AMA Grand National Championship rules that leveled the playing field for makes other than Harley-Davidson, allowing Japanese and British motorcycles to outperform the previously dominant Harley-Davidson KR race bike. The XR-750 went on to become the winningest race bike in the history of American Motorcyclist Association (AMA) racing. The XR-750 is associated with the careers of racers Mark Brelsford, Cal Rayborn, and Jay Springsteen, and was the favorite motorcycle of stunt performer Evel Knievel. Knievel used the bike from December 1970 until his final jump in January 1977. An XR-750 was included in the 1998 ''The Art of the Motorcycle'' exhibition, and one of Knievel's bikes is in the Smithsonian's National Museum of American History ''America on the Move'' exhibit.〔〔 * *〕 ==Rule changes obsolete KR racers== The AMA Grand National Championship Class C rules, introduced in 1933 and revised in 1954, had an equivalency formula limiting flathead, or sidevalve, engines to displacement, while more modern overhead valve (OHV) engines could be a maximum of only . Over time, this displacement advantage kept the older flathead technology on the track and discouraged a broader field of competitors. At least 200 homologated examples of a model had to be built and made available to the public.〔 The flathead Harley-Davidson KR series had dominated Class C racing, but by the late 1960s BSA, Norton and Triumph had little market for 500 cc OHV motorcycles, and there was increasing pressure for a single displacement, without reference to valve configuration.〔 The public was buying and larger displacement British bikes, and they would prove to be competitive, given the chance.〔 With the British marques gaining influence in the AMA, in 1969 new rules were established that there would be one maximum displacement for dirt track racing, 750 cc, with no regard for valve type, though the 500/750 OHV/sidevalve split was kept for the time being in road racing. OHV engines began to dominate racing, in spite of Mert Lawwill's efforts to delay the inevitable on his flathead Harleys, and the KR bikes were a decade out of date and could no longer compete.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Harley-Davidson XR-750」の詳細全文を読む スポンサード リンク
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