oneton,
First, let me welcome you to the forum family. Hope you enjoy your stay!
There are several methods that the forum members here like to use. My suggestion is to try a couple and see which ones you like best.
1. Use a "Sharpie" pen to paint your road wheels. If I'm not mistaken, in the last issue of FSM, this method was used to build the weekend T-34 project. Pretty quick and easy.
2. Use a circle template to paint your road wheels. You can paint the entire wheel and tire flat black, and then find the circle that fits the diameter of the wheel. Put that over your wheel/tire and spray the wheel portion. The template acts as a mask for the tire.
3. Paint the tire portion by hand after spraying the wheel. This can be time consuming, and leave brush strokes, as well as an uneven paint job.
4. Personnally, I like to paint the entire road wheel/tire flat black, then put my airbrush on a fine setting and then "dot-in" (kind of a polka-dot overlap) the base color on the wheel. This allows a little of the black to show through, and gives it a faded effect for the weathering to come. A little overspray on the tire is taken care of with a black wash around the wheel rim after the paint has dried.
Next time, you might try posting your questions like this on the armor forum. There's a ton of good guys and girls there that can intelligently answer your questions about the "dark side" of modelling (as we like to say).
Hope this helps you some.
Gip Winecoff