By 1972 two-stroke dirt bikes had come to the attention of environmentalists, in part due to the noise from their expansion chambers. In 1972 it was estimated that more than five million off-road vehicles (motorcycles, snowmobiles, ATV's, etc) were in use on public lands. Complaints led President Nixon to issue on February 2, 1972, Executive Order 11644, calling for the regulation of motor vehicles on public lands.
Dirt Bike Regulation
ABC News reports that the Vincent Black Lightning upon which Jack Ehret took the Australian National Speed Record in 1953 was sold at auction for $AUD 1.16 million.
Vincent Black Lightning