noun.
Slang for an emergency T-
type spare-wheel for a vehicle. These types of spare wheels are not very wide. Usually a torus-like tire affixed to a steel rim. They vaguely resemble the delicacy of the same name.
Not to be confused with a spare, stock wheel. (As normally seen on Jeeps and large SUV type vehicles.) Stock Spares are frequently attached to the rear
door (on an SUV). Donuts are a feature of some cars, and are store in a
small space in the trunk.
Donuts are very limited in their ruggedness. You can't
go above fifty, and can't go over bumps or anything interesting on the road.