So, maybe I’m missing something here…
I’ve got the weathering down (Thanks to this web page, and people like Swanny). BUT…NO matter what I do, with Dry Brushing, or Weathering, I can’t make my Black wheels look “used” (I can get the hubs to looks good with weathering). I don’t necessarily want them to have Mud on them, just a bit warn down and dirty, like they have been driven A Lot… When I do Drybrushing, it just looks kind of cheesy.
What’s the Secret…
Abastyr
If you are talking about tires with treads, to make them look like they have been through the mud and then driven on drier ground paint the low parts of the treads whatever color mud you are wanting to depict . You can scuff up the tire to give it more of a used look as well. Might try cutting some small chunks out to represent a well worn tire.
As Chris has already pointed out, little nicks and cuts can be made in the surface of the roadwheels giving them a rough surface.
Also using a gray pastel chalk and dusting over the entire suspension will tone down the black of the roadwheel and give the suspension a dusty look.
Maybe instead of painting the tires black, paint them mud coloured, then drybrush with black on the parts that come in contact with the ground.