In Pixar's Cars, the Fabulous Hudson Hornet's first Piston Cup season was 1951.
The Fabulous Hudson Hornet is Doc Hudson's racing identity. In the film's backstory, Doc was a celebrated champion whose career was interrupted after a serious crash. His experiences explain why he dislikes being treated as a forgotten relic and why he initially refuses to discuss his racing past.
The fictional Piston Cup history draws on the real dominance of the Hudson Hornet in early 1950s stock-car racing. The real Hudson Hornet won NASCAR's championship in 1951, 1952, and 1953 with drivers including Herb Thomas and Tim Flock.
The year can be confused with Doc's later championship seasons. The film specifically identifies 1951 as the beginning of his Piston Cup career, while the nearby years refer to subsequent successes in the character's racing history.