Hi PhilD!
Yes, I had the tires off the wheels when I paited them. I used Dupicolor spray paint. It is made for wheels, and then I cleared them with the clear coat they make for wheels. I did about 12 light coats on each to be sure.
I then had the tires mounted and it didn't chip them at all!
Here is a link to the dupicolor
http://www.duplicolor.com/products/wheel.html
It is gun metal, and has a flake to it.