In Pixar's Cars, Rust-eze is painted on Lightning McQueen before he reaches Radiator Springs. Rust-eze is the sponsor that supports Lightning during the first film's Piston Cup season, and its logo appears prominently on his red body.
Lightning initially wants to leave Rust-eze behind for the more prestigious Dinoco sponsorship. Dinoco is associated with The King, the respected veteran champion, so Lightning views it as the sign of having reached the top of the sport.
The sponsor question is distinct from the film's final outcome. Lightning does not simply replace Rust-eze after the championship; his relationship with the sponsor develops as his priorities change. Rust-eze's founders, Rusty and Dusty Rust-eze, help connect the racing plot to the film's broader ideas about loyalty, recognition, and community.