Recycling used tires into rubber mulch is perhaps the best use, so they won't end up in landfills or burned to generate power (yeah, that's a thing!). Neither of those are good for the environment, and if left in a pile they can spontaneously combust from exposure to direct sunlight. Then you've got an ecological nightmare of nasty black tire smoke, which smells far worse than anyone doing burnouts on the road with their vehicle. 

There are about 250 million used tires generated every year in the US. Many of these could have lasted longer if they were well maintained, instead of being replaced, yet most drivers are confused about tire pressure, tire rotation, posses even less knowledge or ability to handle it. Fortunately, the very same reason tires function as well as they do on our vehicles, makes their repurposing, or recycling, last for 25 years or more in the form or rubber mulch or sports in-fill. Recycled tires are even being used in the resurfacing of our roads, freeways and highways, mixed into the upper layer applied to bituminous asphalt roadways. 

The process for making our rubber mulch involves quartering the tires, then placing those into a machine that chops it up into pieces, and with more processing the pieces get smaller and smaller, screening and separating out the various sizes then grouping them for different purposes. For playground or landscaping applications, the optimal size is between 3/8" and 5/8", or a nominal 1/2" sized nugget. If it gets too small, it's not as good for playground fall impact protection, and less effective as a landscape mulch. If it get's too large, then the dispersion isn't as good for initial fall impact protection. Powerful rare earth and electromagnets are used to remove any exposed steel to make the rubber mulch 99.9% steel free. The painting is done by tumbling it, much like a big cement mixer with the paint measured and poured into the tire nuggets tumbling inside. There's a 12-year color loss guarantee, to it stays looking good for a long time.