Looks good to me. But I think you need to make a one special rubber material for people to "adjust". Let me explain.

My problem with rubber is that often there are actually texture maps for the tires, with the white text, bump for the treads, etc. So what is really needed is a material that you can apply that is white, into which you can then plug the texture map, and the bump map. The rubber material you have at present uses the bump channel, so that makes it hard. If you can use the displacement channel for the fine bump texture you have, and leave the bump channel to plug in the map for the tread bump, that will be better, but that is just for me.

For example, here is the texture map that comes with my model.

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