I have an ancient MTD self-propelled mulching walk-behind mower bought in May 1994. One of the rear tires is shredded. I thought I could remove it and bring it to a garden supply center and get the correct replacement. However, when I removed the hub cap, the tire had some kind of gear or ratchet gizmo on it. I tried to turn the center bolt, but it wouldn't budge. I'm an old lady and thought at first I just didn't have the strength, but after sending a photo of it to several hardware stores, the consensus of opinion is that it has something to do with the drive mechanism which, incidentally, no one had seen anything like it before and weren't sure how to proceed in removing the tire. The mower manual doesn't have any info about how to change the tires or even a part number. I tried to find info on the MTD Web site, but the serial number is so old it doesn't apply to walk-behind mowers any longer. It seems such a waste to have to get a new mower when this one still works - it just needs a tire, but trying to work with it is like trying to drive a car with a flat tire. Any suggestions appreciated. Thank you.