I am looking for a good used set of wheels,what is the largest size I can fit?

What is your question?

The standard size wheel is 13 x 4 1/2, 4 lug, 100mm Bolt Pattern. I have had sites recommend diameters as large as 18"; but I am concerned about the fender clearance. Does anyone know how large, both in diameter and width, I can go safely and without complications? I know about offset and will avoid that.