In The United States.

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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.
In the late 70's and most 80's mud bog events, there was generally a class that was for running tractor tired trucks. Trucks like the Arizona Outlaw, Goldbricker, Six Pack, Arizona Sidewinder, Instant Motion, Mud Lord, Mud Pup, Wild Thing, Nasty Habits, Unnamed & Untammed, and the legendary Cyclops were frequent competitors. Some of these trucks would later be modified to be Monster Trucks.
There are many types of mud bogs, from Hill and Hole, Flat or Progressive Track, to Open Bog. They come in many shapes and sizes from 150 feet (46 m) to over 300 feet (91 m). Hill and Hole is just as it sounds, usually 60 feet (18 m) wide 200 feet (61 m) long, a series of hills and holes, and is challenging to each truck. All NMRO tracks are Flat or Progressive tracks, more like a drag strip, or sand drag. Open bogs come from Florida and are mostly natural. These tracks have little organization.
Hill and Hole classes range from 4 and 6 Cylinder, Street Stock, Hot Street, Renegade, Super Street, Small Tire Modified 36" and below, Big Tire Modified 37" and bigger tire, Unlimited, X Class, and More. There are many class usually set but the tire size, and engine.
Most Unlimited and X classes are run with what you want in the safety rules. These trucks have big power engines, built just for that class and are not limited to what can be added to the truck. The truck must pass all safety rules and be safe to put in a show and not hurt the crowd.[3]
National Mud Racing Organization is currently one of the only major professional championship series left. Their rulebook is the general basis for most other mud racing competitions.
Checkered Flag Productions claims to be the best indoor series currently running.
USA Motorsports and USHRA ran professional mud racing series, both referred to as the Indoor Series, for many years until it was phased out of events around 1995. They would occasionally have mud bogs as part of later events, but not on the same scale as before.