I'm always curious about what makes stuff break. I found what I think is a decent summary of the tire aging topic with a lot of references to NHTSA and some interesting insurance industry data:
https://www.liveabout.com/the-scienc...-aging-3234377
My takeaways:
- Oxygen in the air permeates the tire and chemically degrades the rubber and/or interface adhesion. UV exposure is NOT the primary factor.
- Pressurized tires have more oxygen, so degrade significantly faster than those in storage.
- Heat accelerates the processes - both diffusion of the oxygen and the chemical reactions
One thing missing in this article are the probabilities - the consequences of tire failure are bad (life and property damage) but the probability distribution at any given age is going to be very wide.. especially across the huge range of brands and designs. This is why everyone's experience is going to be different and why so many get away with using old tires. Another real world failure risk summary that rivals cam failures.
The article links to one summary of accelerated test development, apparently driven by regulatory efforts:
https://www.nhtsa.gov/DOT/NHTSA/NVS/...ac_SAE2010.pdf
In this summary, there is a chart that illustrates how much variation there is across a relatively small range of tested tires. I assume the markers are specific brands and/or tire designs:
The article doesn't touch on the material and design factors affecting the mechanisms but this chart certainly illustrates "not all tires are created equal".
Don't buy "Black X" tires, buy "Maroon Square" tires !!!
It would be interesting to know which brands put more R&D into this, but the bigger the company, the more liability exposure...
I'm now curious - are there DOT regulations regarding thermal aging of tires in service? Did the NHTSA efforts shared in the article result in testing standards that are now in use? If so, how did it all end up? What failure risk at what time at what temperature was determined acceptable?