These junk tires have limited load capacity as do many other 2/4 ply radials. 11” has a greater load rating which alleviates some if the problem. If I were to use a 9”OEM Bighorn 2 as a spare in the back, I would only do so as a last resort. These tires are real wimpy. This is one advantage to going to 9 or 10 inch 8 ply or 10 ply rated on all four corners.