In Pixar's Cars, the race Lightning McQueen enters after reaching Radiator Springs is the Piston Cup.
The Piston Cup is the film's fictional stock-car racing championship. Lightning is one of three drivers tied for the season lead after the final scheduled race, so a tiebreaking race is arranged at the Los Angeles International Speedway. The event determines the champion and brings Lightning's rivalry with Chick Hicks and The King to its climax.
The championship takes its name from the Piston Cup trophy, which represents the highest prize in the film's racing world. Lightning begins the story focused almost entirely on winning it, but his experiences in Radiator Springs change his attitude toward teammates, rivals, and personal success.
Dinoco 400 is the name of an earlier race in the film, not the championship itself. The World Grand Prix belongs to Cars 2, while the Rust-eze 500 is not the title of the deciding event. The canonical competition name is therefore Piston Cup.