Tire size is not the real issue as stated in one of the above posts, it's what are you going to use the dually for.
If you are going to tow heavy loads with the dually, do not run spacers, in order to get bigger tire sized you usually have to run spacer due to the tire width. If you are going to tow with a dually, you do no want the two rear tires touching, major no no... Big issue with saftey and towing ability. If you are not going to tow big weights, then run spacers and good luck on the size. But like other have said above, make sure you do the reasearch on what you are going to do with it first before you go with tire size. Spacers, big tires, and heavy towing loads equals big problems...
I presonally would love to run a bigger wider tire on my dually, but I tow heavy weights and it just does not make good use of the reason I bought the dually.
Let us know what you decided and show us some pics... Love to see dually with cool looking tires and cool looking lifts. /forums/images/graemlins/thumb.gif
Rob