It seems to be even higher, several studies suggest it's closer to 50%:

https://pubs.acs.org/doi/10.1021/acs.est.3c05002

Three different studies predicted emitted tire wear proportions (TWP and TRWP) of total emitted MP [microplastic] loads in the environment (both aquatic and terrestrial) for around 45%. (6,7,52) These calculations were mainly based on global, annual production data and matched the TWP proportions of around 40% in this study. However, since C-PVC was excluded here, a comparison of the percentages is not trivial.