There are a several ways I’ve seen. What I used do is paint the wheel part first in most cases. I cut a disk of Tamiya masking tape the right size using a drafting compass that has a blade in the arm for the lead, or use a drafting template. Then I spray the tire part. Others with steadier hands put a toothpick in the hole for the axle and turn the wheel with one had while they hold a brush in the other. Wheels that have good definition between the wheel and tiree are easier than ones that do not. Since I bought a scentil cutting machine I use it to make the masks, and whether I paint the wheel or the tire first depends upon the way the tire and wheel meet, and which surface is flatter so the material can conform easily.
I too, paint the wheel color first. But, then cut a mask using a circle template you can get at any craft store, then spray the tires a light faded black. As tires are not truly black. Then unmask and hope the paint doesn’t lift.
Like those above, I paint the hubs first. Next I’ll dilute the paint for the tires to the point where it will run around the rim by capillary action and apply this with a small brush, staying away from the wheel rim itself. Depending on the size of the wheel and how distinct the hub is, I’ll either continue to paint the tire or let the thin coat dry before finishing it.
Hope this will help you; I learned it here on the Forums.
I have a different route, since I have trouble with white paint covering completely. I paint the black first, mask using the above mentioned circle template, then spray the white. It’s kind of a poor man’s preshade.
I paint the hubs first, then when dry, mask them with silly putty. Easy to form in the right shape, then I pain the tyre part using either a brush or spray.
Here’s my method and opinion on wheels. I’m trying to roughly figure how many wheels I’ve painted in my life. Most have three but a B-36 has 10 as does a B-52. Lots, I guess is the answer. Anyway every last one was painted with a brush. There is almost always a ridge separation between the hub and tire. I usually paint the center first and then the tire with a flat brush as shown in this quick shot. A little practice and you’ll be amazed on how smooth an edge you can create. I you mess up, touch up the center and repeat. Actually, tires and wheels are hard to see anyway. inside and up/down positions along with wheel doors can hide small errors. Hey, even an old guy like me can roll out a good wheel!