Tires
The tires that get used on cars are usually made of rubber. To get them sturdy, a process called vulcanization is employed which partially burns, or at least heats up the raw rubber. Still, the rubber on tires wears out and they need to be replaced from time to time.
Manufacturers recommends that tires be rotated to distribute the wear on the tires and keep them evenly worn, as well as keeping the tires inflated to the proper air pressure, as improperly inflated tires can wear irregularly and even reduce the fuel efficiency of the vehicle.
Since the great majority of tires are inflated with air, they can go flat if they pop or leak. Because of this, most cars carry with them a spare tire. To save money, the spare tire is sometimes a smaller, less rugged wheel and tire. These temporary wheels are sometimes referred to as "donuts", and some are not capable of traveling high speeds.
Along with the spare tire or donut, many cars contain a jack and a lug wrench, but many travelers opt to buy "fix-a-flat" which squirts air and sealant into the tire in the hopes of getting into good enough shape to get home or get to a garage.
