If you have difficulty gettig the tire rim over the wheel rim, try usig two tire irons 6 to 8 iches apart. I find this makes the job a lot easier. Also a second pair of hands can make things easier. If your irons aren't smooth/rounded, don't be afraid to take a metal file to them to round off all edges. It does't take much to pinch a hole into an inner tube. Lubricating the iner tube, and even the rim, with liquid dish soap can also make the job go more smoothly.