I have to replace my tires every 60 000-100 000 KM as the tires wear down and the rubber comes off as I drive. If this is happening with all cars, why arnt the roads coated in rubber? Is somebody cleaning the tire rubber off the road? Is it getting washed away from the rain and into drains/the ocean? How long does it take for rubber to degrade that has come off the tire?
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Why are you assuming that the loss takes place in the form of adhesion to the road surface? It’s rubber, not paint, so the loss is often in the form of fine dust that simply becomes airborne. Some heavier particles do settle on the road, but as you suspected they get washed away.
It’s better to think of this as producing rubber “dust” of varying particle sizes, and then the reason why the roads aren’t covered becomes obvious. Wind, runoff, and road cleaning as you suspected.
You need to basically melt rubber to get it to stick to the road- which is why you see it at race tracks, but relatively few tyre marks on the road. Normal wear and tear doesn’t do it at all, wheelspin and slides and locked wheels do it and most people do very little or none of that.
For the most part, your tyres just wear into very fine dust and then wash and blow away (with all the obvious environmental issues that brings with it, you breathe a lot of tyre in your life even if you don’t present Roadkill). Modern tyres are made out of a bunch of different ingredients and it breaks up a little as it wears so there’ll be carbon black (soot, basically), silica, etc as well as the base rubbers.
Over 100000 km, your tyres wear down by, what, 10 mm max? This means that they wear down by 10^-2 / 10^8 = 10^-10 metres per metre travelled.
One metre is about the circumference of your tyre, so you can imagine leaving a one atom thick, one metre wide (each tyre is something like 25 cm wide) layer of rubber behind you as you drive. One lane of road is, say, 5 metres wide, so to reach a one mm thick layer of rubber would need fifty million cars to drive that lane, which is more than one a second for a year. This is more than current cars and drivers are capable of.
Also, think about it: rubber wears off other rubber in the tyre thanks to friction with the road. That same friction is also acting on the rubber on the road, which is much less well stuck in place than when it was part of a tyre.
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