Mountain biking entails the sport of riding bicycles off-road, often over rough terrain, whether riding specially equipped mountain bikes or hybrid road bikes. Most mountain bikes share similar characteristics that underscore durability and performance in rough terrain: wide, knobby tires, large, round frame tubing, front fork or dual suspension (aka shock absorbers). The durability factor means a far heavier bicycle weight to rider ratio than their road touring cousins.
Mountain biking is roughly broken down into four categories: cross country, downhill, freeride, and trials/street riding. Each has differing levels of safety-consciousness with different types of mountain bikes and riding gear.
Mountain bikers have faced land access issues from the beginnings of the sport. Areas where the first mountain bikers have ridden have faced serious restrictions or elimination of riding.
Many trails were originally fireroads, animal paths, hiking trails, or multi-use paths that were simply used for these new trail users. Single-track mountain biking creates more conflict with hikers, particularly in forested areas. There is also some concern single-track biking leads to erosion. Because of these conflicts, the interpretation of the Wilderness Act was revised by the National Park Service to be able to exclude bicycles in certain areas.