On my stock 14" Magnums, not sure if they are 5.5" or 6" wide, when I went to National Tire and Battery, I think I was told the widest you can SAFELY mount was a 235/60-14. He looked it up in a book he had. Can you do it? Sure. Should you do it? Up to you. If the rim isn't wide enough, the center will bulge and as Chryco mentioned you won't get even tire wear.