My 100-6 has 4 tires with less than 5k miles but are 12-15 years old. They appear to be in good shape with no visible cracks and run smooth. I'm in a dilemma if I should replace them since they are so old or just keep them and not worry about it. What brought this on is my spare tire needs replaced so I have 2 choices, 1- buy 4 new tires and use the best old tire as the spare, or 2- only buy a spare. What do you guys think? I'm only driving the car 1000 miles a year with speeds under 70mph.