If a tire has lots of small cracks making squares or rectangles on the surface of the sidewall, suspect it. Eventually the rubber will separate from the steel belts, and you will have all the fun of blistered, out of balance, one-side-larger-than-the-other tires.

Rubber also tends to get harder as it ages, so you have less traction even if the tread is still good.

Six years old and sitting in one spot most of the time, the tires also won't be particularly round anymore, so you will get vibration.

Plan on new ones soon.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!