To clean model railroad wheels, you can use a chemical cleaner like isopropyl alcohol or mineral spirits on a paper towel or cotton swab, or use mechanical methods like a Dremel with a wire brush. For rolling stock, running the wheels over a chemically dampened paper towel placed on the track works well. For locomotives, you can either clean them by hand, or use a purpose-built wheel cleaning brush that sits on the track and rotates the wheels when powered.