There are nearly half a billion cars on the road in North America. This staggering figure has one thing in common with rare exception, they all have four tires, each. Given that they are consumable materials, it is estimated that about 350 million tires are disposed of each year. As such, the processing, transport, wear and disposal of these tires is a massive concern, partly because they are so large and durable.
Almost without fail they are made from petroleum products instead of natural rubber, which was phased out in the 1960s. Often they also contain steel belts for additional stability, too. Since the mid-20th century, the life of tires has increased significantly, and this life-span can be increased with proper inflation, wheel balancing and rotation. But eventually, the tread wears too thin to be safe and they must be replaced.
Recycling of tires into other materials such as basketball courts, artificial turf and road surfaces is a very common end to the life of a North American tire, since warehousing them has been identified as a fire hazard and a mosquito breeding ground by environmental scientists.
