ANOTHER QUICK TIP - WEATHERING TANK WHEELS
Many W.W.II tanks ran on steel wheels with hard rubber 'tires'. On tanks that used relatively wide road wheels, the rubber tire surfaces were fairly prominent and clearly visible. But even on narrow wheels (like those on German Panther or Tiger tanks), there was enough rubber tire surface to be clearly seen on a 1:35 scale model.
The assembly instructions for most model kits tell you to paint the tire portion of each wheel 'flat black'. This is fine if you're building a 'factory fresh' model of the tank. Rubber tires (tanks, trucks, jeeps, etc.) were subject to heavy weathering from salt water (as when exiting a landing craft on D-day), mud, rain, gravel, and just about anything else that might have come in contact with them. A combat vehicle did not have to be in the field very long before its tires began showing wear & weathering effects. In many cases this meant the 'flat black' color of a factory-new tire turned to a duller, ashy-gray color. This was rarely a uniform change and some areas of a tire might show more weathering than other areas.
To give your tank (or truck or jeep, etc.) a more realistic 'in the field' look, you can use this simple procedure
to weather your vehicle's rubber tire surfaces:
1. Spray paint the entire wheel (including the tire area) whatever color you're painting the rest of the vehicle. This provides a base coat onto which the tire coloring can better adhere.
2. Create a black wash by mixing flat black paint (I use Tamiya XF-10 Flat Black) and rubbing alcohol (NOT water!). Thinning your paint to the consistency of a heavy wash with alcohol causes the paint to dry much faster and much duller, giving you the worn-out ashy appearance you want for your tires. Thinner washes generally produce a more dramatic effect, but require multiple applications to get complete coverage. I suggest that you experiment with thinning your paint and apply different densities of wash to your kit's sprue or other unneeded plastic surfaces (or even unseen interior areas of the model) to determine the right ratio of alcohol to paint for the weathering effect you want.
3. Brush on the wash, carefully covering the entire rubber surface of the wheel. Allow this coat to dry completely. Repeat as needed to get the dark ashy finish you want - DO NOT worry if some areas are darker than others, an uneven finish is more realistic than a totally uniform finish in this case!
Another approach is a technique sometimes called 'color scaling'. Instead of using a true 'flat black' paint as per the kit instructions, use a paint like Badger's Grimy Black or Weathered Black; both these 'black' paints dry to a dull gray finish. You can then apply a thin wash of flat black over the dry Grimy or Weathered black paint to create an uneven weathering effect. Again, thinning the paint with a little alcohol will produce a duller / flatter finish.
A newer alternative is available from more recent paint products (Vallejo or Mission Models) in a color called Tire Black. This paint dries to a dull off-gray color that does a good job of representing road-worn rubber. Here, you may want to apply a wash of flat black over the Tire Black just to give the final finish a more natural unevenly worn look.