XCO (Or cross-country) is the only mountain bike discipline hosted as an Olympic discipline, and globally the most popular mountain bike discipline. Of all mountain bike disciplines, XCO offers the most fun and consists of lap racing around a short circuit containing various obstacles.
XCM (Or marathon) is the most popular discipline in SA. Marathon (XCM) is perhaps the toughest form of mountain biking because riders often have to cover more than 80 km in one race on mountainous terrain.
DHI (Or Downhill) is a time trial event. Riders start at intervals that can vary from 30 seconds to three minutes-depending on the stage of the competition - and the rider with the lowest time wins. As the name of this discipline implies, DH races are held in steep, downhill terrain, resulting in higher speed than in cross-country racing.