safety rules to govern monster trucks. The organization still plays a major role in the sport's development in the US and EU. With racing taking precedence, several teams began to think in new ways as to how the trucks could be built. Towards the end of 1988, Gary Cook and David Morris debuted Equalizer, a truck with a combination of coil springs and shock absorbers as the main source of suspension rather than the standard of leaf springs and shock absorbers. In 1989, Jack Willman Sr., now with his own truck, Taurus, debuted a new truck which used a solid axle suspension system made of parallel four-link suspensions and coilovers that together weighed in at close to . However, the biggest innovation came from Chandler, also in 1989, when the CAD-designed Bigfoot #8 debuted featuring a full tubular chassis and a long-travel suspension system made of triangulated four-link suspensions, bump stops, limit straps, cantilevers, and shock absorbers charged with nitrogen gas. The truck revolutionized how monster trucks were built, and within a few years most top-level teams built similar vehicles. In 1991, TNT was purchased by the USHRA and their points series were merged. The Special Events championship began to grow in popularity with teams as it had open qualifying spots which the invite-only USHRA championship did not have. The Special Events series lost its Pendaliner sponsorship in 1997. The short-lived ProMT series started in 2000. Even though racing was dominant as a competition, USHRA events began having freestyle exhibitions as early as 1993. These exhibitions were developed as drivers, notably Dennis Anderson of the extremely popular Grave Digger, began asking for time to come out and perform if they lost in early rounds of racing. Promoters began to notice the popularity of freestyle among fans, and in 2000 the USHRA began holding freestyle as a judged competition at events, and now awards a freestyle championship. Promoters The USHRA's Monster Jam series, now owned by Feld Entertainment, is currently the largest, touring through the United States, Canada and select regions of Europe. Other promoters of monster truck events include the Toughest Monster Truck Tour, the Monster X Tour, and Hot Wheels Monster Trucks Live. Truck construction The first monster trucks built were pickup trucks and SUVs that were modified with larger suspension and larger tires. Today, trucks now have custom built tubular chassis, with four-link suspension to provide up to