I have talked to many tire experts and they all told me on my 91 motorhome, 81 DeLorean and 65 Corvair, that ANY tires over 7 years of age should be replaced. I let the motorhome tires go to 7 years and on inspection they looked good with no cracks in sidewalls or separation between tread......at 8 years the side wall layers were pealing although the tread looked and measured almost new.....it has 12K miles on them. I replaced them. My DeLorean has 8k miles on it and as it is over 20 years old, they will be replaced soon. They still look and measure like new, but they are hard and brittle! It is my second or third car and does not get much use and I rarely go out on the highway at any speed with it so have been lucky so far. Murray Vin: 05962 Lic: DMC-XII