An actual test under actual driving conditions....

Subject: 123 240d.

Age of spare which had never been on the ground: 21 years.

Condition of spare tire: Brand new. It looked fantastic.

Speed of test: 70 mph. (Yeah, I lived a few blocks from an interstate.)

Miles before it blew out: Six.

This was on a Sunday morning, out in the country when traffic was almost nothing. I pulled over, put on the tire I had switched out, and learned that no matter how great a tire might look age make fools of them all.