I have a 97 f150 xlt 4X4, i currently have 265/70R17s on it, what is the biggest tire size i can go with out modding anything and no rub, i would like to keep the same width, 265/XXR17, i think 265/85R17 witch is about a 35" tire will work but not sure

 

You can fit a 315/70-17 (35x12.50) by using the OEM wheels. But, they will rub the frame at full steering lock. Anything smaller should have no rubbing at all.