In Pixar's Cars (2006), Lightning McQueen is traveling to the Piston Cup when he becomes stranded in Radiator Springs.
The Piston Cup is the championship competition at the center of the film's story. McQueen is a talented but self-centered rookie race car who finishes a three-way tie in the season finale, forcing a tiebreaker race in California. While being transported there, he falls from his trailer and ends up in the isolated desert town.
The name is a deliberate reference to NASCAR's former Winston Cup, which Pixar used as part of the film's stock-car racing world. McQueen's goal is initially to win the trophy and secure a lucrative sponsorship, but his time in Radiator Springs changes his priorities. He learns about friendship, teamwork, and the value of the town's history.
The Piston Cup should not be confused with the later World Grand Prix in Cars 2. That international event is a separate competition involving races in Japan, Italy, and England.