Wheels Wobble But They Don't Fall Off

This morning I had plans to meet my father and grandfather for breakfast.  I told my wife that I would drive her car so that I could fill it up with gas for her before she drove it to teach her dance classes today.  She absolutely hates putting gas in her car, so I thought that I would help her out.  On the way to breakfast her car started bouncing really bad.  I could tell that it wasn't something that would keep me from making it to breakfast, but I also knew that it was something that was going to have to be taken care of today.  My initial thought was that a wheel bearing went out, but I wasn't sure.  I made it to breakfast and had a great time.  While I was walking to the car I started thinking again about what the problem could be.  Since my father and I are both fairly mechanically inclined (we are the types that have the philosophy of "Why pay someone to do it when you can do it yourself?) I asked him to take a ride with me to see if he could help me diagnose the problem.  Before leaving, though, I went around to both wheels and tried to shake them to get an indication of a wheel bearing being loose.  The wheels felt nice and tight, so I pretty much ruled out the bearings then and there and started leaning towards a tire issue.  When we started driving you could really feel it wobbling.  I could let the steering wheel go and you could actually see it going back and forth.  My dad and I both came to the conclusion that it must be a tire.  I called my wife and told her to take my truck to dance classes because of the issue with her car.  I drove home and pulled the car into the garage and put the car onto jacks to pull the front wheels off.  Sure enough, when I pulled the driver's side front wheel off I could see a spot where the tire belt started separating from the sidewall.  The passenger side had a spot where it looked like it was about ready to do the same thing.  We had ran into this problem before and had replaced two of the four tires, but these two tires were the ones that had not yet been replaced.  The bummer is that tires are expensive, but the good thing is that my wife wasn't driving somewhere and had an issue where the tire came completely apart and caused an accident.  I suppose that there was a reason that I drove her car this morning instead of my truck because if it wouldn't have happened to me this morning odds are that she would have had an issue on her way to work Monday morning.  I guess this means that I am going to be running to the tire store to get a couple of tires replaced this afternoon, but I have to wait until my wife gets home with my truck.  Oh well, what else would I want to do with myself on a Saturday afternoon?  :)