During the first race montage, Lightning is shown coming into the pits. Once in his pit box Guido can be seen and heard undoing multiple lug nuts on his left front, but when the new tire goes on, only 1 lug nut is tightened before Guido moves to the back tire.
It is not explained why the cows don't immediately tip over when woken up suddenly, as shown in the first two films.
At Thunder Hollow, Cruz (under the name Frances Beltline) has the number #20 sprayed on her right side. When we see her during the talk with Smokey and the other veterans, it is now on her right side. Later she has it spray-painted on both sides when practicing with McQueen (in order to substitute for Jackson Storm, who's racing number is also #20) but this is after McQueen talks to Smokey.
When McQueen places Cruz's demolition derby trophy on his ramp, it is right against the edge of the ramp when viewed from the front but much farther away from it when viewed from the back.
After Cruz switches with Lightning in the final race, some of the racers are missing for the rest of the race.
Darrell Cartrip says that there are 43 cars competing in the Florida 500. However, there are only 35 next-gen race cars and one Lightning McQueen. So essentially, there are only 36 racers competing in the Florida 500. There are still some other non-next-gen cars left besides McQueen.
Natalie Certain says that every week, veteran racers retire or get fired to make room for the next generation racers. However, the season was almost over when more next generation racers started to push out the stock cars, so veteran racers leaving every week is impossible. At the start of the film, the season is nowhere near over yet. In fact, there were at least six more races (which we know because at one point it is announced that Storm has won seven races in total) before the final race, and Certain makes her statement right before this final race. With one race every week, there are plenty of opportunities for cars to retire or be replaced.
It makes no sense for McQueen to say 'car wash'. It's like people saying 'human shower'.
When Lightning rolls over in the wreck , the 95 on the driver side is almost completely scraped off , but later when he is in Doc Hudson's old garage , the numbers are untouched even though he is now covered in gray primer .
After Cruz Ramirez wins the race in Florida, Ryan Laney and Bubba Wheelhouse's voices are switched when congratulating Cruz.
Mcqueen is covered by Grey primer , but yet he still has his number 95 perfectly painted on both sides of him .