The 25 year old radial tires on my Firebird ruptured a belt during winter storage with about 6,000 miles on them. Yet my 40 year old Le Mans had a PERFECT crack free original spare, and my compact spare is also in great shape with no cracks.

Exposure to sunlight, heat, ozone and chemicals make a big difference in longevity. So does load, and maintaining adequate but not excessive pressure. I would still not use a tire more than 10 years old for normal driving, and less for performance driving. For a trailer queen, I'd use the originals.

Anyone remember tubes? They still make cracked belted tires reasonably safe to use at low speeds.