[Sirrotica]

The bonding of the rubber to the steel belting is what does modern tires in. When the bond starts to be compromised is when the parts inside start delaminating from each other.

The Firestone debacle years ago was said to be due too the fact that the materials that the steel belting were made from, were stored outside. Rust started on the steel cords, and that made the bond of the rubber to steel was compromised from the beginning. No one can look inside of a tire after manufacturing to see if the steel to rubber bond is compromised, so there is no way that eyeballing the outside of a tire can determine if the core parts are breaking down. This is the reason that some people can run tires for 15 years without incident, and others fail internally at 5 years.

Radial tires are much more suseptible to belt failure than bias ply tires are, due to the angle the belts are in relationship of each other. The belt angle is also the reason that the old bias ply tires could have sidewall punctures repaired, and radials can't have sidewall repairs. The fact that radial belts don't criss cross in the sidewalls, makes the sidewall rip from the bead to the treads, ending the life of he tire.

That's how I understand the reasons given by manufacturers for radial tire failures, YMMV.