Tire Failure Case: Manufacturing Defect
In 2011, a single vehicle incident occurred on an interstate in California. A passenger vehicle was heading eastbound when the right rear tire failed. According to the police report, the right rear tire had a tread separation. Once this occurred, the vehicle fishtailed, lost control and went off the left side of the road. As it went off the road, the vehicle rolled several times before it came to final rest facing in a northwest direction.
1) The subject right rear (RR) and companion left rear (LR) tire were produced by the same manufacturer and branded in the same plant in the 40th week of 2007. Both tires had the same DOT code, which meant they were the same size, brand, construction and produced in the same plant during the same week of the year.
2) Based on the DOT code, the rear tires were approximately 4.1 years old at the time of the incident. Based on the service records, the rear tires had been in service for approximately 3.2 years at the time of the incident.
3) The subject tire had numerous areas of chafe and polish, which were indications of internal separations. The internal separations of the subject tire became so large that they resulted in a full tread and outer belt separation.
4) The subject tire had several areas with internal pattern marks present. This was a manufacturing defect and caused or contributed to the internal separations and ultimately the tread and outer belt separation.
5) The subject tire did not have signs of over deflection, impact damage, misuse or abuse that would have caused or contributed to the tread and outer belt separation.
6) The subject tire was defectively designed because the manufacturer did not employ a full nylon overlay to mitigate the known propensity of steel belt radial tires to fail by belt edge separation. The use of a full nylon overlay would have delayed and/or prevented the subject tread belt separation.
7) The subject tire had signs of oxidation cracking on the sidewall of the tire. This indicated that the tire sidewalls were aging. However, this did not cause or contribute to the failure.
8) The X-ray results of the companion tire showed dogear, gap and overlap splices present. These were manufacturing defects. At these same locations, the shearography showed internal separations. This was due to the high stresses and strains present at the belt edges of the tire. When the belts are not manufactured and positioned properly, localized stress and strain concentrations can occur. Even though the companion tire appeared normal and not remarkable on the exterior, on the interior separations had formed. If the companion tire had continued in use, it would have eventually experienced a tread and outer belt separation just as the subject tire experienced.
9) No recalls, defects investigations or service bulletins were found for the subject tire on the NHTSA website.