This is what we found on Wikipedia regarding the Hot Wheels Monster Trucks Live:

A monster truck is a specialized off-road vehicle with a heavy duty suspension, four-wheel steering, large-displacement V8 engines and oversized tires constructed for competition and entertainment uses. Originally created by modifying stock pickup trucks and sport utility vehicles (SUVs), they have evolved into purpose-built vehicles with tube-frame chassis and fiberglass bodies rather than metal. A competition monster truck is typically 12 feet (3.7 m) tall, and equipped with 66-inch (1.7 m) off-road tires.

Monster trucks developed in the late 1970s and came into the public eye in the early 1980s as side acts at popular motocross, tractor pulling, and mud bogging events, where they were used in car-crushing demonstrations. Today they are usually the main attraction with motocross, mud bogging, ATV racing, or demolition derbies as supporting events.