are recycled tires a better replacement for sheet rubber?

I'm practicing shoemaking, learning how to make shoes that promote healthy feet, fit better than storebought shoes, and are more environmentally friendly. One of the biggest costs is buying rubber soling material to attach to the outside of the leather midsole. Also, the manufacturing of synthetic rubber is not environmentally friendly, while the harvesting of most natural rubber is not done in an ethical way.

(I realize that some shoes just have leather soles, but I've found they tend to be slippery.)

Some people cut soling from used tires. That is cheap, and turns a difficult waste stream into something useful.

On the other hand, there are toxicity concerns with used tires.

Is there any information about how the rubber in tires stacks up against any other rubber product? I bought some sheet rubber material, and it certainly has a "rubber smell" to it.