Rear End Loose at 45 MPH
 

I have a lowered 97 Eclipse my son just purchased and just noticed some "movement" in the rear end when he gets around 45mph. I didnt notice it when I drove it home when we bought it (about 50 miles away), but did notice this past weekend when replacing the front pads and rotors that the drivers rear tire was almost flat. I put air in it and it has been holding air ever since, but now have this "movement" in the rear end at around 45mph. (Its almost like when you hit a small patch of ice in a rear wheel drive car) One other thing my wife noticed was that the rear passeneger tire is slightly larger than the rest of the tires. Passenger rear tire is 205/60/R16 and the other three are 205/55/R16. I'm thinking that when I put air in the flat tire that it may have contributed to this? Is the difference in tire height enough to cause that? If anyone has seen this before or has an idea of what I should check, please let me know. I appreciate your help!

PROBLEM SOLVED. I couldnt believe the difference in tire height from a 205/55/16 to a 205/60/16. It was significant (shows how much I know about tires, lol). I purchased a good used tire at the local junkyard and had it mounted and balanced and the problem went away.