93w3504x4duelly

I was wondering what is the biggest tire size (height/width)that a duelly could run on the rear with no spacers on the rim with stock size 16/8 wheels the tire stores are no help they tried to sell me some 235/75/16 stock size but I said no I want taller to increase the rollout and drop some rpm current setup is 235/85/16 General AT a small bump in size and it helps it looks like I have plenty of room I want to fill up more of the wheel well area plus this is a cheap lift.

thanks for the input