The BMX bicycle is a small human powered machine originally designed to mimic the performance of the motorcycles built for off road racing and trail riding. These motorcycles are today referred to as motocross or Moto X motorcycles. The initial appeal of the BMX styled bicycles was the fact that the rider could emulate some of the movement of a motocross motorcycle at a fraction of the cost. BMX is today the generic description given to any of the bicycle motocross styled machines. The BMX is distinct in both style and construction from the larger, all-terrain mountain bike.
The precise origins of BMX cycling are not certain. It is likely that as early as 1969 BMX bikes were being used in California by teenagers to ride on self-built tracks that incorporated both straights and manmade bumps and moguls. The BMX historians point to the 1970 film "On Any Sunday" as the first public display of the capabilities of BMX machines. By 1974, there were full-fledged organizations in California to promote BMX racing. The international body that governs all BMX racing, the BMX Federation, was founded in 1981.
The favored original BMX designs were short, solidly constructed frames with 20 in (50.8 cm) diameter wheels. The BMX bike placed the rider lower to the ground, making the bicycle easier to maneuver around the obstacles of a race course, as well providing the rider with an ability to better absorb the forces directed upwards into the bicycle frame and the rider. The seat is angled upwards from the frame, often at an angle of approximately 70°, to provide the rider with an upright body position. Most frames of higher performance BMX racing machines are constructed from aluminum. The tires on a BMX bike are constructed with an aggressive tread to assist the rider in obtaining traction on the dirt race courses.
In recent years, the BMX bicycles have been adapted for use as freestyle performance machines. BMX bicycles, with their low profile and handling characteristics, are used on skateboard facilities such as half pipes. BMX riders perform stunts involving the bicycle being used in jumps and flips. Where BMX racing had definite elements of danger created by the speeds of the bicycles and the unpredictability of the dirt racing surfaces, BMX freestyle was a bona fide extreme sport. As with any of the sports in the extreme classification, BMX freestyle is primarily aimed at the gratification of the rider and the conquering of the risks assumed in the freestyle routine.