Downhill mountain biking (DH) is a time trial event held on a steep, rough terrain that often features jumps, rock gardens and other obstacles. Downhill bikes are heavy, strong, and feature front and rear suspension with over 8 inches of travel, to glide quickly over rocks and tree roots. A continuous course is defined on each side by a strip of tape. Riders have a single attempt to reach the finish line as fast as possible, while remaining between the two tapes designating the course. Riders musts 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, he must return to the course at the point of exit. 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.