In 1985 and 1986, Lammers made 10 CART World Series starts for four different teams. His best finish was fifth at Laguna Seca Raceway in 1985 for Forsythe Racing. He was entered and practiced for the 1986 Indianapolis 500 in a Mike Curb entry, but did not make a qualifying attempt. He finished 26th and 22nd in points in his two seasons, respectively. After that he turned his attention to sports car racing.