I've read on another forum that there were several mistakes in the film. I didn't notice it when I watched it though. Here they are.
Mistake #1
When Lightning McQueen is in Radiator Springs and he's trying to fix the road with Bessie the first time, a little bit of asphalt spurts on him and drops on his famous lightning bolt sticker. The size and position of the patch of asphalt changes throughout the movie until it gets washed off.
Mistake #2
During the very last race, Lightning McQueen gets next to the green car, and the reflection of that green car's chrome "C" emblem is seen on Lightning McQueen's hood. However, the C is facing the right way. Since the C is placed on the green car in the correct direction, the reflection on Lighting McQueen should be a mirror image.
Mistake #3
Stock cars always race with slick tires (no tread) and when you see the tires (on and off the cars) at the racetracks in the movie, they're slick. In Radiator Springs however, Lightning's wearing treaded tires, even though he went from the track to the trailer and from the trailer to Springs without a tire swap.
Mistake #4
When Lightning Mcqueen's body is redone in Radiator Springs, the change does stay when he is in the Piston Cup. However, after the Piston Cup, back in Radiator Springs, his body is the re-do, just with the Lightyear wheels instead of his redone ones.
