Motorcycle racing takes a variety of forms, each with its own rules and specialized equipment. The best known is road racing, in which cyclists race in categories, usually related to engine size, over special circuits or on public highways closed for the occasion. Motocross is conducted on a closed circuit over rough, cross-country terrains and natural obstacles. Dirt-track races are held on oval tracks found primarily at fairgrounds. Other forms include Trials, Hill Climbing, Endurance Runs, Ice Racing, Hare Scrambles, and Cross Country. The Canadian Motorcycle Association was formed in 1946 to organize competition when motorcycling became a popular competitive sport. In 1967 Canada hosted a World Championship Road Race for the first time, followed by a Motocross and a Trial in 1975, and a Superbike race in 1989. In 1967, a Canadian team participated in the international Six-Day Trials, the "Olympics of Motorcycling." Mike Duff placed second in the Road Race World Championshionships in the 1960s. In 1972 John Williams, of Markham, Ontario, won the World B Division Hill-Climbing Championship.