Would have guessed the opposite, FWIW, on the grounds that the bad stuff is hard materials (like mine dust). But if anyone actually knows that would be interesting. How good a measure is total PM2.5 or whatever, without asking about what it's made of?
That said, as was pointed out below, changing the car's design to vacuum up brake dust would be much easier than getting away from rubber.
Yeah, you generally shouldn't be inhaling dust but inert dust (silica -> silicosis) is better than reactive dust (asbestos -> cancer).
I'm not well versed enough on the specifics to tell you whether or not PM2.5 is a good measure of pollution. The experts in the subject of air pollution routinely use it so it can't be thaaaat bad.
That said, as was pointed out below, changing the car's design to vacuum up brake dust would be much easier than getting away from rubber.