10yrs must. Otherwise depends on sticky or loss of traction or weathering cracks. I dumped snow tires for M3 at ten years because they lost dry and wet weather traction, not snow traction. With Michelin pilot cup tires and 3-5k miles per ear I get maybe 5 years before they get hard from heat cycling or age. New tires are definitely better traction if somewhat squirmy for500 miles...My tires have 80% tread left but are approaching 5yrs old. Should they be replaced soon due to age? What do others think about lifetime of tires before replacement?