A BMX bike is a type of popular bicycle used both for sport and casual riding. It is designed principally for motocross and dirt riding. BMX racing began in California in the 1970s. The Schwinn String-Ray model was the vehicle of choice. By the middle of that decade, so many children were racing that manufacturers began creating bikes specifically for the sport. The American Bicycle Association was founded in 1977 as a national sanction group for the sport. The first world championships, under the auspices of the International BMX Association, were conducted in 1981. BMX Freestyle – made up of dirt, vert, park, street, and flatland disciplines – is now a staple standard part of the annual Summer X Games.