The only info I've ever seen was an article saying that the rear rims were widened police steelies.
I did some more investigation and found out the tires are Mickey Thompson ET -Streets. If you take that fact plus the fact that the dodge police wheels only come in 18" you can then look up the different sizes that the ET Streets come in an 18" rim.
You then get these possibilities:
If I had to make an educated guess by looking at the pictures i'd say they were 305/45/18, but that's just a guess!