I was reading today about
Zipper Rupture in tires, which injures and kills its share of tire technicians. There is a video of mannequins being destroyed in tests
and of a tire being destroyed in a shop
.
The failure mode is interesting. The tire is run at low pressure for some reason, for example it's run flat. Or it's simply overloaded. The sidewalls over-flex. The steel cords in the sidewalls undergo
work hardening because they are flexed many thousands of times. The hardened cord breaks instead of flexing. The tire later bursts in the sidewall at the point of broken cords. It's called "zipper" because there are steel wires to the left and right of the rupture, which look like an open zipper. The burst is so sudden that it sends the tire flying, potentially killing people in the way.
It's not inconceivable that some of our blowouts start with broken cords due to over flexing, and the rubber over the broken cords bursts, then the tire disintegrates. Lots of folks have commented on the suddenness of the blowout, well here's a reason for that to happen.
We've been thinking about the cause for tire failure in TrailManors as rubber degeneration due to age. Steel belt failure doesn't really have anything to do with the rubber. One of the safety features of the nylon overlay in premium trailer tires is that it is not subject to work hardening, and thus will retain the pieces of the tire in place through a steel belt failure.
This is a pretty strong argument for running your tire at the cold inflation pressure on the sidewall, and
not below that pressure. Cord flex increases with lower pressure.