Tire Maintenance - Spare Tires

Spare Tires

Vehicles typically carry a spare tire, already mounted on a rim, to be used in the event of flat tire or blowout. Many spare tires (sometimes called "doughnuts") for modern cars are smaller than normal tires (to save on trunk space, gas mileage, weight and cost) and should not be driven very far before replacement with a full-size tire. A few modern vehicle models may use conventional spare tires. Jacks and for emergency replacement of a flat tire with a spare tire are included with a new car. Not included, but sometimes available separately, are hand or foot pumps for filling a tire with air by the vehicle owner. Cans of pressurized air can sometimes be bought separately for convenient emergency refill of a tire.

Some modern cars and trucks are equipped with run flat tires that may be driven with a puncture over a distance of 80 km to 100 km. This eliminates the need for an immediate stop, and the associated expensive tow service or tire change.

Interestingly, tires actually get more traction when they are bald, because there is more surface area making contact with the road. The reason consumer-use tires have treads is to avoid hydroplaning when the surface of the road is icy or wet. Conversely, stock cars driven on professionally-maintained NASCAR tracks use tires with no tread, but a much thicker layer of rubber.