Lightning McQueen uses the number 51 when racing as Doc Hudson in Pixar's Cars 3.
During the Florida 500, McQueen changes from his familiar number 95 into Doc Hudson's old racing identity. He paints his car in Doc's blue color scheme and races with number 51, honoring the mentor who helped him understand racing, friendship, and persistence. The change is part of McQueen's decision to support Cruz Ramirez rather than simply reclaim the spotlight.
McQueen's usual number is 95, which appears throughout the Cars franchise. Doc Hudson's number 51 connects the final race to his earlier career as the Hudson Hornet. The number is therefore not a random replacement or a new permanent identity; it is a tribute used for a specific race and emotional moment.
The number 43 belongs to The King, while 20 is associated with Jackson Storm's racing identity. Those numbers can create confusion because all three cars compete in the same racing world, but 51 specifically represents Doc Hudson in the Florida 500 sequence.