Tractors are car-versions of cows. Their cousins are bulldozers, who are seen in Mater's Tall Tales. They have a droopish eye appearance in some parts of the movie. They are referred as stupid tractors by Mater. They're usually seen grazing in the morning until evening and upside down in the night due to tractor tipping activities caused by Mater. They are very slow moving but in a rampage, they are very fast. Frank is a "bull" that lives in the same field as them (even though he is not a bulldozer, like the other "bulls"). They are not dangerous.
They appear when Mater decides to take Lightning McQueen tractor tipping. Later, they appear in McQueen's dream of Frank winning the Piston Cup, when a stampede comes into Radiator Springs, and at the Radiator Springs Drive-In Theatre.
In Cars Mater-National, they appear in the Tractor Tippin' mini game. Like in the original game, the goal is to tip all the tractors before time runs out, and try to avoid getting caught by Frank or the lamps.
In the third video game in the series, they appear in a mini game called Tractor Stampede. There are tractors stampeding all over Radiator Springs. The goal is to tip all 10 before time runs out, and there is no Frank to watch out for.
Although they don't appear, their mooing can be heard at one point in the first Cars level when the player drives through a field with Mater and Sheriff.
In Radiator Springs Racers, Sheriff asks Mater to take the riders to the big race. Mater takes them tractor tipping, but then they wake up Frank and run away into Radiator Springs to get ready for the race.