"Donut" tires, commonly known as spares, are intended to be driven for no more than 70 miles. They are supposed to only be used under emergency situations, as they tend to have less than the recommended tread depth of normal tires.
A donut should not exceed more than 50 mph when being used on a vehicle. Because these tires have smaller tread areas, they lose a lot of traction capabilities as compared to other stock tires. This can also negatively impact the vehicle in other ways, such as causing the differential of a car to damage the vehicle's clutch disk and drivetrain components.