Most truck and auto tires these days are made of rubber and steel.  They start out as a loop, called a bead, that is constructed with a rubber coated cable made from steel.  This is the inner armature that gives the tire the necessary strength to stay firmly affixed to the rim of the wheel.  This inner skeleton also allows the tire to withstand the impact of the machines which mount the tires to the rims. The body of the tire is then constructed by applying layers of various fabrics, the most common of which is cords of polyester.  These run opposite the tread pattern in radial tires.  Older tires were made with these cords running diagonal to the direction of the tread.  This is all then coated in rubber, which serves to seal the air in and to bond all of the fabrics and cords together. The strength of a tire is dependent on how many layers of fabric with which it is constructed, these are called plies.  Most auto tires are made with two plies.  This is compared to a commercial airplane tire which will be made with as many as thirty plies or more.  This gives one the idea of the greatness of the carrying capacity that is necessary for those big jetliners.  In steel belted tires, or radials, the band of steel is placed just under the rubber, making the tire virtually puncture proof, as well as ensuring that the surface of the tire remain flat to the road, providing the optimum amount of traction. As one drives, the friction of the road causes a tire to heat up. Tires that will be best suited for driving at high speeds are made with extra layers of polyester to aid in keeping all of the components of the tire in place.  The side wall of the tire also provides stability, and serves to protect the plies of the body and prevent the escape of air.  Tread is constructed quite often times with a mix of different synthetic and natural rubber.  All of these components are used and constructed with the utmost car to ensure that people will be safe on the road.