Downhill biking (DH) is a time trial mountain biking event held on a course with a net decrease in elevation. As the name of this discipline implies, downhill races are held on steep, downhill terrain, resulting in high speed descents, and with extended air time off jumps and other obstacles. A continuous course is defined on each side by a strip of tape. The width of the course can vary greatly over the length of the course, but it is typically between about 2m and 10m wide. Riders have one attempt to reach the finish line in the shortest amount of time while remaining between the tape. The rider must choose their path (or line) by compromising between the shortest possible line and the line that can be travelled a the highest speed. If a rider leaves the course by crossing or breaking the tape, she 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.
The 1st downhill time-trial race took place in Fairfax, California on October 22, 1976 on a fireroad now referred to as Repack Road, due to the need to repack the single rear hub brake after a descent. The bikes used were based on beach cruisers that had a single rear brake that worked by pedalling backwards. A mechanism came into operation causing a conical metal (bronze?) brake shoe to be wound on a thread into a conical metal hub. To prevent a metal to metal brake from snatching it was always filled with grease. Heavy use of the brake during the descent would cause the brake to over heat, melting the grease till it drained from the hub and required repacking. Ten riders descended 1300 feet of Repack in about 5 minutes.[2] The first bikes used for descending were known as "klunkers" or "paperboy bikes": coaster brake cruisers using balloon tires first imported to America by Ignatz Schwinn.[3] By 1979, two organizers and competitors of the Repack downhill, Charlie Kelly and Gary Fisher founded the company which named the sport, MountainBikes.[4] As mountain biking grew enormously during the 80s, downhill riders continued to use either rigid or limited suspension travel (under 2 inches) bicycles, and purpose made downhill bikes were not made until the 90s. Some of these innovations included dual crown suspension forks and disc brakes, as well as very elaborate frame suspension designs.
Later, riders from all disciplines of cycling began focusing on downhill. Particularly, many BMX racers made the crossover, including champions such as John Tomac (Team Tomac Bikes), and Brian Lopes. Their influence is seen in the increased difficulty of many courses, especially the big jumps and drops aspect of downhill. The coming of age for downhill biking was its inclusion at the first UCI Mountain Bike Championship, held in 1990 in Durango, Colorado.
Modern downhill bikes weigh between 14 and 19 kg (30 and 42 pounds), and usually feature full-suspension and frame geometries that lean back farther (slacker geometry) than other mountain bikes. As of 2006, 203 mm (8-inch) is the 'norm' for suspension travel however some commercially available big mountain freeride bikes can have over 300 mm (12-inch). Large-diameter 203–5 mm (8-inch) hydraulic disc brakes moderate speed. Downhill bikes and freeride bikes are similar but there are some slight differences. Downhill race bikes typically are much lower and have slacker head angles than freeride bikes, so that the bike is more stable at speed and in corners. Freeride bikes have a steeper geometry and a higher bottom bracket height, so that they are better for balance and maneuverability, however freeride bikes sometimes use single crown forks, which are shorter in travel length and lighter than the dual crown forks often used by downhill riders, dual crown forks usually have around 200 mm (8-inch) of travel, and single crown forks are usually around 180 mm (7 in) maximum.
Downhill gear features body armor and full-face helmets; helmets are often rated by CE, CPSC, and ASTM standards, however rarely by DOT or Snell, Other protective gear such as a neck brace can be added to reduce the risk (by bringing the head to a controlled stop)[5] of neck and spinal injury.
