- The spare tire may be identical type and size to those on the vehicle. The spare may either be mounted on a plain steel rim or a matching road wheel as found on the vehicle. Among passenger vehicles, full-sized spares are usually provided for sport utility vehicles and light trucks, since a "limited use" spare would adversely affect such vehicles with higher centers of gravity. Due to the size of the full-sized spare, it is often mounted on the outside, such as the rear door of SUVs, and occasionally on the front hood.
- Certain vehicles are provided with a "limited use" spare tire, also known as "spacesaver" or "compact" spare tire — in an attempt to reduce cost, lower the vehicle's weight, and/or to save on the space that would be needed for a full-size spare tire. The spare is usually mounted on a plain steel rim. They are typically smaller than the normal tires on the vehicle and can only be used for limited distances because of their short life expectancy and low speed rating. As well, due to the different size of a donut compared to regular wheel, electronic stability control and traction control systems will not operate properly and should be disabled until the original wheel is restored.
- In some cases, automobiles may be equipped with run-flat tires and thus not require a separate spare tire. Other vehicles may carry a can of tire repair foam, to repair punctured tires, although these often do not work in the case of larger punctures, and are useless in the event of a blow-out.
A spare tire is an additional tire (or tyre - see spelling differences) carried in a motor vehicle as a replacement for one that goes flat, a blowout, or other emergency. Spare tire is generally a misnomer, as almost all vehicles actually carry an entire wheel as a spare, as fitting a tire to a wheel is very difficult without specialised equipment, and is not practical in an emergency. However, some spare tires ("space-saver" and "donut" types) are not meant to be driven long distances and most of them have maximum speed of around 50 mph (80 km/h).
The early days of motor travel took place on primitive roads that were littered with stray horseshoe nails. Punctures (flat tires) were all too common, and required the motorist to remove the wheel from the car, demount the tire, patch the inner tube, re-mount the tire, inflate the tire, and re-mount the wheel. The first to equip cars with a spare wheel-and-tire assembly were the Ramblers made by Thomas B. Jeffery Company. The Rambler's interchangeable wheel and mounted spare tire meant the motorist could quickly exchange it for the flat one. The punctured tire could then be repaired at a more convenient time and place.
The pre-mounted spare tire and wheel combination proved so popular with motorists that carrying up to two spare tires became common. Automakers often equipped cars with one or dual sidemounts. The spares were mounted behind the front fenders as they blended into the running boards (a narrow footboard serving as a step beneath the doors).
In 1941, the U.S. government prohibited spare tires on new cars. Shortages of resources caused by World War II led to quotas and laws designed to force conservation, including rubber that was produced overseas and difficult to get. A similar ban was also implemented by the U.S. during the Korean War in 1951.
Contemporary vehicles may come equipped with full-size spares, limited use minispares, or have run-flat capability.
Spare tires in automobiles are often stored in a spare tire well – a recessed area in the trunk of a vehicle, usually in the center, where the spare tire is stored while not in use. In most cars, the spare tire is secured with a bolt and wing-nut style fastener. Usually a stiff sheet of cardboard lies on top of the spare tire well with the trunk carpet on top of it to hide the spare tire and provide a pleasant look to and a flat surface for the trunk space.
Other storage solutions include storing the spare in a cradle underneath the rear of the vehicle. This cradle is usually secured by a bolt that is accessible from inside the trunk, for security. This arrangement has several advantages over storing the tire inside the trunk, chiefly that it is not necessary to empty the contents of the trunk in order to access the wheel. The arrangement may also save space in some applications; however it has disadvantages too, such as the fact that the tire gets very dirty, making the act of changing the tire more unpleasant. The mechanism may also rust on older cars, making it very difficult to free the spare. The cradle arrangement is usually only practical on front wheel drive cars, as the cradle would get in the way of the rear axle on most rear or four wheel drive cars. A similar arrangement is also often found on trucks where the spare is often stored beneath the truck bed.
Many SUVs and off-road vehicles have the spare wheel mounted externally – usually on the rear door, but others may mount them on the bonnet, the side or even the roof.
In mid-engined and rear-engined cars the spare tire is generally stored in the front boot and a dedicated spare tire well is seldom used.
Some vehicles stored the spare tire in the engine bay, such as the Renault 14 and older Subaru vehicles, such as the Subaru Leone.
Vehicles like the Volkswagen Beetle used spare tires for ancillary purposes such as supplying air pressure for a utility system.
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