There are several things to look for...the easiest thing to look for, is a date code that's over 10 years old. Or over 5 years old if you're really paranoid. I recently had a tire come apart sitting in my garage, mounted on a rim, but not on a car...it had a 3 digit date code, so it was at least 15 years old. I think I took it off the car around 2009. One of my unfounded pet theories is that it's just not easy to make rubber and steel stick together, so steel belted radials want to come apart after a while.