Harley-Davidson's XR-750 has ruled dirt-track racing for more than two decades. In fact, no other race car or motorcycle has won as many races over such a long time period. And the victories continue today. This is the story of the legendary XR-750 from its development in 1970, when it was created to replace the aging KR. The first XRs used iron cylinder heads and barrels-and were painfully slow. By 1972, the motorcycles were redesigned with...