A monster truck is a specialized truck with a heavy duty suspension, four-wheel steering, 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.