In 1984 he teamed with Mike Baldwin to win the Suzuka 8 Hours endurance race.[1] He is a three-time AMA Superbike Champion, winning in 1984/5 on the VF750 and 1986 on the VFR750F.[2] He jointly holds the record for the most wins in a season with Mat Mladin.
In 1988 the Superbike World Championship began, with Merkel entered on the RC30. He won the championship from Fabrizio Pirovano and Davide Tardozzi with two wins and three other podiums.[3] He successfully defended the crown in 1989, with 3 wins, 7 other podiums, and 4 poles. He took three more wins en route to sixth overall in 1990, but was less competitive after this.
Merkel retired from racing at the end of the 1995 season after being injured in an accident at Firebird International Raceway in Chandler, Arizona. Merkel and his family moved to a ranch they owned in New Zealand. He lives there with his wife Carla and son Travis, and as of the summer of 2009 welcomed newborn son Jhett.