Cruz Ramirez uses car number 51 when she races Jackson Storm in Pixar's Cars 3.
Cruz begins the film as Lightning McQueen's high-tech trainer at the Rust-eze Racing Center. She is talented but has been directed toward coaching rather than competing. McQueen's decision to support her racing ambitions leads to the climactic competition against Storm.
The number 51 connects Cruz with Doc Hudson, whose historic Hudson Hornet also raced as number 51. The detail makes her final race more than a new contest: it links the film's younger racer to Doc's legacy and to McQueen's own transformation into a mentor.