Why do radial tires fail when overloaded or underinflated?

 I have a number of posts here on the topic of why tires fail. There are also more than 16 posts that mention "separation" or more accurately a "Detachment", as a reason or contributor to a tire failing. But maybe, some readers want more a scientific explanation.

 

This graphic is a computer-generated color depiction of the relative heat generated internally in a tire as it is driven down the road. Light blue is the coolest area, and red is the hottest.

When tires crack

I have covered the "artificial aging" of rubber in several posts. Basically, the molecular cross-link density increases, which can be thought of as stiffening and less flexibility. When rubber loses its flexibility, the molecular bonds crack. As more bonds crack, these cracks join up until they can be seen with the naked eye, as pointed out with the yellow arrows in the picture below.

 

 When tires develop these larger cracks, they simply grow over the next hundreds or thousands of miles, as seen in the next picture.

"Free-Spin Inspection"

Tires with these larger cracks can be identified by doing a "Free-Spin Inspection," as covered in detail in this post on how I inspect my tires.

When doing a "Free-Spin Inspection", If you discover the out-of-round or side-to-side movement as seen in the video in the above post, I strongly suggest you have the tire inspected by your tire dealer for that brand tire, or simply replace the tire if it is more than 3 years old.

By the way, the steel belts do not "slip". They are no longer attached as part of the structure of a radial tire.

 

I hope this helps understand the situation.