Mud bogging (also known as mud racing, mud running, mud drags, or mudding) is a form of off-road motorsport popular in Canada and the United States in which the goal is to drive a vehicle through a pit of mud or a track of a set length. Winners are determined by the distance traveled through the pit. However, if several vehicles are able to travel the entire length, the time taken to traverse the pit will determine the winner. Typically, vehicles competing in mud bogs are four-wheel drives. The motor sport is overseen by sanctioning bodies like the American Mud Racing Association, and the National Mud Racing Organization (NMRO), that oversee each class, develop and maintain the relationship with track owners to provide a racer and fan-friendly facility, ensure the sponsors get a good return, and help govern the sport.
A modern top level Class V or VI mud racer is a dragster-style "rail" design, with a supercharged engine and/or nitrous oxide injection. Engines may be in the front or the rear of the vehicles. Vehicles are required to have four wheel drive, in order to assure that the vehicles have the best possibility of avoiding being stuck. The sole difference between Classes V and VI is the tire type. Class V racers have D.O.T. street legal mudding tires for traction. Class VI vehicles have tractor tires.
Early mud boggers were pickup trucks or sport utility vehicles modified with lifted suspensions and larger tires, and classes exist for such vehicles today. Engine upgrades were also common. In the late 1970s and early 1980s, large tractor tires became popular, and the drive lines required to run such tires led to some of the first purpose-built mud bogging machines. By the late 1980s, many sanctioning bodies began giving precedence to vehicles with modified, and lower, dragster-type "rail designs", as they had increased in popularity. At the same time, superchargers first became widely used, leading to the modern top-level racer.