Wikipedia: Downhill mountain biking

 

Downhill mountain biking (DH) is a genre of mountain biking practiced on steep, rough terrain that often features jumps, drops, rock gardens and other obstacles. Downhill bikes are heavier and stronger than other mountain bikes and feature front and rear suspension with over 8 inches (20 cm) of travel, to glide quickly over rocks and tree roots. In competitive races, a continuous course is defined on each side by a strip of tape. Depending on the format, riders have a single or double attempt to reach the finish line as fast as possible, while remaining between the two tapes designating the course. Riders must choose their line by compromising between the shortest possible line and the line that can be traveled at the highest speed. If a rider leaves the course by crossing or breaking the tape they must return to the course at the point of exit, unless they do not gain a time advantage from crossing the tape, in which case they can continue with their run. Riders start at intervals, often seeded from slowest to fastest. Courses typically take two to five minutes to complete and winning margins are often less than a second. Riders are timed with equipment similar to that used in downhill skiing.