>Tire factories start with bulk raw materials such as synthetic rubber (60% -70% of total rubber in the tire industry[2][3]), carbon black, and chemicals and produce numerous specialized components that are assembled and cured.

Looks like most of the rubber used these days is synthetic[1], usually made of styrene and butadiene which could easily degrade into base monomers or at least shorter chains.

1. https://en.m.wikipedia.org/wiki/Tire_manufacturing

Car and light truck tires are apparently only about 19% rubber.[1] More than half of a tire's composition is synthetic polymers, fillers, and textiles (e.g. polyester, rayon, nylon).

[1] https://www.ustires.org/whats-tire-0

Tires generate more particles of pollution than exhaust.[2] EVs are good. But eliminating car exhaust apparently isn't the big car pollution problem.

[2] https://www.theguardian.com/environment/2022/jun/03/car-tyre...

A car tire is not purely rubber, it is combined with synthetic polymers derived from petroleum and petroleum derivatives (same as plastics).