It varies. I tend to do it by hand, usually. If there is a sharp demarcation between the rim and the tire on the kit part, I apply a strong wash of dark gray to the outside of the raised lip and let capillary action take the wash around the tire. The color will concentrate at the rim. Once dry, I can brush the dark gray freehand to cover the rest of the tire and have a neat edge at the rim.
If I plan to paint all the wheels off the tank, I sometimes use a draftsman's circle template. Spray the whole wheel and tire dark gray, then mask the rim with the template and spray the camouflage color on the wheel.
A third shortcut applies to vehicles in muddy conditions (can you say "Eastern Front," boys and girls?). Don't paint the tires at all! Just paint the whole track run and suspension with the local earth color. Add a darker brown wash and dry brush with a lighter tan to bring out the detail. You can texture the mud with acrylic gel medium or Gunze Sangyo Mr. Surfacer, if you like.

Low power & low speed minidrill, insert piece of straight sprue,
spin and file to slight cone which fits in axle-hole of wheel.
Find another bit of sprue which is thick enough and redo the
above until satisfied.
Mount wheel on cone, spin at low speed, use thumb of the hand
holding the minidrill (left hand if you use the right hand for holding
the brush) as brake-shoe to reduce speed if needed.
Adjust the wobble until it isn't irritating.
Hold paintbrush in the other hand with small amount of paint,
apply brush to the wheel/"rubber" starting from the running surface
and slowly move the brush inwards towards the edge of the rim.

Experiment with rpm and dilution of paint to get a combination
which works for You.
All 64 "circles" for the road wheels of a Pz IV takes about 10-15
minutes with a little practice.
If paint splatters all over the place or the wheel goes flying off
then the speed is way too high. Too much wobble and/or wheel
falling off is usually caused by a too steep cone, the coning
should be barely visible.
/ Robin