Tyres are unfortunately plastics in this day and age as well.

As for the share of microplastic pollution, both rank about equally as high: 35% for clothes, 28% for tyres (…europa.eu/…/microplastics-sources-effects-and-so…) - this as a share of directly released particles that make it into the ocean.

Note the interesting fact of fishing nets, plastic bags and bottles making up the vast majority of plastic in the ocean, however.