>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