A tire is a flexible container for compressed air which supports the vehicle's load; propels a vehicle forward, helps the vehicle turn; stops the vehicle; and cushions the load from road imperfections. Modern tires have about 20-25 different components. Tires are engineered and built from the inside out, starting with an inner liner which gives the tire shape and holds in air. Fabric belts are wrapped around the inner liner. The tire's bead is fastened to the bottom of the fabric belts and holds the tire to the wheel.
On top of the fabric belts are steel belts, which serve to give the tire stability and keep the tread pattern as flat as possible and maximize contact with the road. The tire tread is added on top of the belts, with different tread patterns for different types of tires. The sidewall on the side of the tire gives it stiffness and ride characteristics. A taller, softer sidewall will absorb more bumps, while a shorter, stiffer sidewall will provide better cornering ability and sharper steering response.
On the sidewall of every passenger-car and light-truck tire is an alphanumeric code that describes the dimensions of the tire. For most tires, this code will start with a "P" (above, left). Some may start with an "LT" to signify light truck. Some tires may have a "Max. Load" indication (above, right). When selecting new tires, it is important to make sure a tire's load rating is at least a high as the tire you are replacing.