A tire (North American English) or tyre (Commonwealth English except Canada) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which the wheel travels. Most tires, such as those for automobiles and bicycles, are pneumatically inflated structures, which also provide a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint, called a contact patch, that is designed to match the weight of the vehicle with the bearing strength of the surface that it rolls over by providing a bearing pressure that will not deform the surface excessively.
The materials of modern pneumatic tires are synthetic rubber, natural rubber, fabric, and wire, along with carbon black and other chemical compounds. They consist of a tread and a body. The tread provides traction while the body provides containment for a quantity of compressed air. Before rubber was developed, the first versions of tires were simply bands of metal fitted around wooden wheels to prevent wear and tear. Early rubber tires were solid (not pneumatic). Pneumatic tires are used on many types of vehicles, including cars, bicycles, motorcycles, buses, trucks, heavy equipment, and aircraft. Metal tires are still used on locomotives and railcars, and solid rubber (or other polymers) tires are still used in various non-automotive applications, such as some casters, carts, lawnmowers, and wheelbarrows.
Unmaintained tires can lead to serious hazards for vehicle and vehicle operators, ranging from flat tires which can lead to damage to the vehicle, to blowouts, where tires explode during operation. The manufacture of tires is often highly regulated for this reason. Because of the widespread use of tires for motor vehicles, tire waste is an extremely large portion of global waste leading to widespread need for tire recycling, through both mechanical recycling and reuse , such as for crumb rubber and other tire-derived aggregate, and pyrolysis for chemical reuse, such as for tire-derived fuel. Waste tires, if not recycled properly or burned, can release toxic chemicals into the environment. Moreover, normal use of tires produces micro-plastic particles that contain these chemicals that both enter the environment and affect human health.
