Formula racing
Simpson started in drag racing and SCCA Formula racing, eventually moving up to the USAC Championship Car series. He raced in the 1968-1974 and 1976-1977 seasons, with 52 career starts. He qualified twentieth for the 1974 Indianapolis 500, and finished thirteenth. He finished in the top ten 11 times, with his best finish in 6th position in 1970 at Milwaukee. He decided to end his racing career in 1977, because he started to think about a telephone call that he needed to make while he was practicing at Indianapolis Motor Speedway.