Campeonato Alemán de Superturismos
Maassen began his career in karts, and moved to cars in 1989, in Formula Ford 1600. During the early 1990s, he raced in the German Formula 3 series. His F3 career includes a win at the prestigious Macau Grand Prix in 1994. From 1995 to 1997, he raced touring cars for Nissan in the Super Tourenwagen Cup.