On the road until it gets washed away.
The rubber wears on the road and shoulders of the road.
They'll get burnt to the heat
Friction. Every time you accelerate or stop, there's a little bit of slippage that rubs away the rubber, bit by bit. Without that friction, you would never go anywhere, and if you did get moving, you would never stop.
If you look on the roads, you will see the distinct stripes where cars tires go...that's the layer of rubber left by all the cars that travel there.
Where does all the rubber from car tyres go? Rubber car tyres slowly loose while driving?
