What are the biggest tires I could put on a ram 3500 without making any changes(lift kit). The wheels will probably be 16 X 8.

I believe that the largest tires you can put on a Ram 3500 4x4 1994 to present are 33x12.50. If you add an inexpensive ($150 or less) 2" front leveling kit, you will be able to fit 35x12.50s.