Harley Davidson motorcycles have participated in dirt track racing in the United States from the beginning. In the '60s, the AMA introduced a 21 cubic inch class which was ideal for the Aermacchi Harley Davidson 250s. This machine enjoyed considerable motorcycles racing success both in dirt track racing and even in the Isle of Man at the TT where an example recorded an average lap speed of 99.32 mph in the 1970 races.

In 1965 a modified version of this bike recorded a world record speed over the measured mile hitting 177.25 mph.