I have tried a few different methods of painting my wheels, and wanted to share my experiences and the method that I feel gives the best results, and the least amount of work or steps to complete. When I first started these 3d projects, I tried painting my wheels before assembling to the truck frame, after assembling to the truck frame, painting black first and then silver for the wheel, painting silver first and then black for the tire, primer first and then color, and no primer and painting color only.
What I have found is that primer works very well on the truck body and cab, but will just build up on the details on the wheels. So for my aluminum wheels, I use a rustoleum spray can and paint a couple of coats directly on the raw print. For steel rims, I still use primer, and then hand paint the rims whatever color I want.
What about timing of tires and wheels? Well, I find that painting silver first, and then hand painting the tire black yields the best results. I have designed the front tires with an exaggerated rim where it meets the tire so that a steady hand with paint brush can flow the paint right up to the rim and leave a nice crisp line between tire and wheel. The rear wheels are a little easier in that I just use a silver Sharpie marker around the inside of the rim to make a perfect line between rim and tire.
As I have posted before, my recent design revisions to place the wheels in a square pattern on the sprue rather than a straight line has seemed to influence the print orientation. I am getting my wheels printed flat now, which results in very clean prints. As you can see in the photos, the lug nut detail is present on all wheels. Take a look at my Kenworth T2000 and you will see that the quality of my wheels has come a long way from the early days.