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Case Studies

RV Tire Failure Analysis Case

RV tire failure analysisAn RV owner noticed that his RV was pulling to the right. He stopped at a retail shop of the large tire manufacturer. The tire shop provided an alignment and recommended a tire rotation, moving the right front tire to the rear of the RV and the rear tire to the front of the RV.  A few months after this rotation, the owner was on a trip in Arizona when the left front tire blew out.  Thankfully the occupants were unharmed, but the tire failure led to more than $150,000 in damages.  Our tire expert, was retained to conduct a tire failure analysis.

CASE BACKGROUND

A tire failure occurred on Interstate 10 in Arizona causing thousands of dollars in damage to a 2014 Aspire Entegra Coach recreation vehicle (RV).  The driver was heading westbound on Interstate 10 when the left front steer tire failed. Once the tire failed, the vehicle was pulled left of center across the roadway where the driver was able to bring the RV to a controlled stop.

PRIOR MAINTENANCE

Five months prior, the Aspire RV was taken in for an alignment at a tire service shop affiliated with a large tire manufacturer. During the visit the Aspire RV had an alignment performed, and it was noted that the right front tire had increased wear on the outside shoulder. The service personnel recommended rotating the right front tire to the rear position to even out the treadwear. The Aspire RV had 21,553 miles on the odometer at the time of the service. According to the tire shop invoice, this rotation was completed between the right steer tire and the right front outer tires. The rotation occurred even though the steer axle tires were a different size compared to the tires on the second and third axles tires.

DAMAGE DUE TO TIRE FAILURE

The Aspire RV electrical compartment that housed the electrical panel with the various fuses was located just forward of the left front wheel well. When the left front tire failure occurred, it was very violent. The tire fragments damaged the electrical compartment. Additionally, the floor tiles within the cabin were cracked from the tire impacting the underside of the floor.

The failed left front tire was sent to the tire manufacturer for evaluation.  After inspection of the tire, they stated that the tire had failed due to over deflection.  Over deflection can be caused by underinflation or overloading of a tire.

TIRE FAILURE ANALYSIS & CONCLUSIONS

The left front tire was no longer available for inspection. However, our expert was able to complete the tire failure analysis by analyzing 30 digital photographs of the RV and failed left front steer tire and conducting a thorough inspection of the RV.

FINDINGS INDICATE INSTALLATION DEFECT

  1. Based on DOT code on the tire wall, the left front tire was approximately 3.9 years old at the time of the failure. Additionally, the DOT code of the front tires on the Aspire RV at the time of the inspection were the same as the subject left front tire (minus the date code).
  2. The right side tire (size 275/80R22.5) that was rotated to the right front steer position by the tire shop should not have been installed on the front steer axle. It was the incorrect size and was not the recommended 295/80R22.5 size for the front steer axle. It was smaller in width, smaller in diameter, had a smaller static radius and had a lower load carrying capacity. This was an installation defect (see table below).
  3. The 275/80R22.5 tire that was installed on the right front steer position at the time of the left front steer tire failure had both shoulders worn with reduced tread depth. This was consistent with a tire that was overloaded. This tire was overloaded because it was a smaller diameter and had a lower than required load carrying capacity.
  4. With the larger tire (size 295/80R22.5) installed on the left steer position and the smaller tire (size 275/80R22.5) installed on the right steer position; the front of the Aspire RV would have been leaning to the right side with ultimately more load. The footprint pressure distribution of the left front steer tire would have shifted to the right as well. In simple terms, the inboard side of the left steer tire footprint was loaded more than the outboard side of the footprint (i.e. increased negative camber). This would have increased heat and deflection on the inboard side of the left front steer tire.
  5. The left front steer tire failure was consistent with being caused by the installation error completed by the tire service shop.

Because We’ve Always Done it That Way

Most of us have heard the story about the person cutting off both ends of the ham before baking a holiday dinner. When asked why, the response was, “Because that’s how we’ve always done it.” Later you find out that great, great grandmother’s pan was too small forcing her to cut off the ends of the ham so that it would fit in the pan.  Generations later, the ham is still being chopped off on both ends. As forensic engineers, we are called to seek answers to the question “why?” Why did something fail?  Why did the accident occur?  And sometimes, “Why has it always been done this way?”

Tire Failure Case

tire failure analysisOur tire expert was called out to examine the right front tire of a tractor trailer due to a tread separation. Fortunately, the tire stayed inflated (100+psi), and the driver was able to bring the big rig to a controlled stop. When our engineer interviewed the shop owner, they stated that they have had a contract with this tractor trailer manufacturer for more than three years. Our expert learned that since the start of the contract, the shop has reported having 27 front tire failures on 36 of this popular brand of tractor trailer.

That’s a 75% failure rate.

Interview & Inspection

tire failureThe inspection of the tire failure indicated that the tire had been overloaded/under-inflated. Our expert interviewed the driver of the tractor trailer and the head mechanic of this trucking manufacturer. Both stated that they check tire inflation at least twice a day and set pressure to 110 psi.

When asked why they set the front tire pressure to 110, they stated, “We have always done it that way.” They then explained that when they get their trucks serviced from the manufacturer’s dealership, the dealership sets the front tire pressure at 110 psi as well, “So, it must be correct.” Our expert walked over to the door placard on the tractor trailer and pointed out that the placard states that the front load range H tires were to be inflated to 120 psi. Not only was the dealership (and subsequently the clients shop) inflating the tire to the incorrect pressure, but the dealership was also putting on incorrect load range G tires (less load carrying capacity) as opposed to the correct load range H tire (higher load carrying capacity). This was the dealership!

Being Curious & Asking the Right Questions

I once had a manager tell me that he wanted to hire people who are “curious,” people who are inquisitive, who have a desire to learn or to know how things work. Regardless of occupation, curiosity is important in today’s world. We need to know that the information we are receiving is correct, and part of that is knowing its origins. Having a little less ham for the holidays may not be a big deal, but having a catastrophic tire failure is.

To visit our full line of services, visit the U.S. Forensic website.

Tire Failure Case: Manufacturing Defect

Background Information

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.

Our Findings

  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 tire 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 (tire defect) 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.

Tire Defects & Other Causes of Tire Failures

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