Don't boil with the rims or other plastic parts in there. It can deform them. I have 2 ways I do it. I have a old coffee maker that is perfect then for larger parts I have a old crock pot. These get hot but not too hot. They will not deform the parts. I have left wheels in them for a couple of days and never had a problem. I was able to dye 2 40 series wheels at a time in the crock pot and 8 2.2 rims at the same time. Leaving the parts in there for 24 hours or more will allow the dye to penetrate deep into the plastic. This is great because if you scratch the part it will still be dyed. One cool thing you can do is get high temp wax and melt it and paint patterns in the plastic. This works 2 ways. It sometimes keeps the total original color showing, but sometimes the dye will penetrate a little and be a little less dyed than the rest. When it works it is too cool. If it dosen't you just remove the wax with soap and real hot water and put it back in the dye and the effect will be covered and will leave no trace.