Here in Washington we don't have a legal tire size limit, it's all about bumper height:
Occasionally you'll see some pretty custom-fabricated bumper setups.The maximum bumper heights will be determined by weight category of gross vehicle weight rating (GVWR) measured from a level surface to the highest point on the bottom of the bumper. For vehicles exempted from the bumper requirement for the reasons stated above, a maximum frame elevation measurement shall be made to the bottom of the frame rail.
Maximum heights are as follows:
7,501 lbs. to 10,000 lbs. GVWR
Adding an additional bumper will not meet the above requirements.