For the past decade, and perhaps longer, there have been many incidents of tread belt separations in passenger-vehicle tires; some of these separations have resulted in loss of vehicle control, often with serious consequences. Although a manufacturing defect in a tire can result in a tread belt separation, it is not the only cause. Based on my experience in examining failed tires, manufacturing defects are not the primary cause of failures in tires for highway use. The tire shown above is one which would have resulted in a catastrophic tread belt separation had it remained in service. It was my tire, and I observed that it was coming apart in time to have it replaced before it failed. The story and more pictures follow.
This tire had been in service on my pickup truck for nearly 60,000 miles. It was nearing the end of its normal service life, but it still had remaining useful tread depth. As I was driving one day, I used the controls for the driver information center and noticed that the left rear tire was 5 psi low. As I watched, the pressure remained steady at that level. When I arrived home, I did a cursory examination of the tire. Not observing a problem, I inflated it to the proper pressure. The next morning, it had not leaked any air. I kept an eye on tire inflation pressures for the next several days, and the left rear tire never lost any air. About a month later, I randomly checked pressures again while driving and noticed that the left rear tire was 5 psi low again. When I arrived home, I did a little more careful examination of the tire, but I did not jack up that wheel to enable me to examine the complete circumference. Once again, I noticed nothing unusual, so I added some air. The next morning, it had not lost any air, so I drove and monitored tire pressures for about a week. No change, so I all but forgot about it.
Approximately another month later, as I was returning to my truck from a visit to the grocery store, I noticed a screw in that left rear tire, located at the top of the tire as it stood at rest and almost exactly centered in the tread. I drove to my tire retailer, where the screw was removed and the puncture was properly repaired.
Fast forward some indefinite number of weeks to the morning of March 21, 2009. For a while, I had been noticing some unusual noises which sounded tire-related, but I had never spent the time to investigate the cause; I knew I was going to be getting some new tires before too long, anyway. I stopped at a friend's house to talk to him about an unrelated vehicle matter; as we were talking, he remarked that my left rear tire didn't look right. It didn't take much discernment for me to realize what was happening and why.
The first of the three photographs below shows a crack in the tread shoulder above the region of the edge of the upper tread belt. This was a steel-belted radial, which is the most common type of tire in current use in passenger vehicles. The next photograph shows a missing piece of the tread shoulder, exposing the edge of the tread belt, which is beginning to separate. The third photograph shows another region where a piece of the tread shoulder is missing, and the shoulder is torn to the sidewall. This is most probably the region where the tread belt would have first released sufficiently to begin the process of peeling away the tread cap and outer belt, which process finishes very rapidly after a significant portion becomes loose in a tire on a vehicle traveling at normal highway speed.
Manufacturing defect? No. At some time during the unknown months of operation of this tire with the penetrating screw, air or some other contaminant found its way into the tread plies of this tire. Most probably, if I had discovered the penetrating screw shortly after it punctured the tire and had it promptly repaired, the tire would have served me well until the groove depth was at or very close to 2/32 inch, at which point I would have replaced it. This is the type of thing that one would usually never discover after the in-service tread separation: when that type of failure occurs, all of the tread is typically separated from the tire, and finding evidence that a tire had been repaired is not, by itself, sufficient evidence of the cause of the tread separation, except perhaps if the patch or repair demonstrates improper technique.
An object does not need to penetrate the tire to or through the inner liner to create an injury site at which air, moisture, and/or dirt can enter the tire structure and begin a process that will result in failure by ply or belt separation if it is not discovered before the failure occurs. With those cases especially, once the tread cap is gone (they are almost never recovered to be presented for examination with the rest of the carcass) there is little hope of finding specific evidence of the cause of the failure.
Please call me anytime you wish to discuss a tire failure, vehicle accident reconstruction, or any of the other vehicle-related consulting services I offer. Thank you for reading my current feature.
If you wish to return to the home page, you may click on this link.