Gravel racing is one of the newest disciplines of bicycle racing, emerging in the 21st Century.  The distinguishing features of gravel racing include long distances, often 100 to 200 miles, and mass starts that include all categories of racers. The bicycles and courses in gravel racing vary widely, from road bicycles with wide tires used on smooth gravel roads to bicycles that are similar to mountain bike used on courses that include technical trails.