Why Defective Tires Cause Deadly Accidents
- May 8, 2013
- Vehicle Defects
The importance of tires on a vehicle safety is highlighted by a popular tire advertisement. The picture is of a baby placed in the middle of a tire with the tag line “you have a lot riding on your tires.” Unfortunately, over the last several decades, tire manufacturers have knowingly sold defective tires to the unknowing unsuspecting public with the result of causing unnecessary deaths and injuries. The most recognizable familiar instance is the Ford/Firestone case, but Michelin, Cooper, and other manufacturers have been forced to take corrective actions as a result of tire litigation as well.
Tread Belt Separation
Although tires can fail in a number of different ways, the most dangerous failures, and the ones most associated with serious accidents, is the tread belt separation. Other types of failures include blowouts, sidewall failures, and run flat failures, but there are many reasons for these failures to occur that have nothing to do with manufacturing defects or design defects. Furthermore, it is generally accepted that these failure modes do not create as dangerous a driving situation, and therefore do not cause as many accidents, as does a tread belt failure.
Understanding Tire Components
To understand tire-tread belt separations and the defects that cause them, it is first important to understand the different components of a steel belted radial tire and how they are generally manufactured. Tires are far more complex than they may appear on the outside. The basic components of a tire, from inside to out, include the inner liner, polyester reinforced body plies, steel belts, tread, sidewall and tire beads. The inner liner is made up of halobutyl rubber and is designed to retain compressed air inside the cavity of the tire and prevent migration of air into the structure of the tire. The polyester reinforced plies and the steel belts combine to provide puncture resistance as well as allow the rubber to maintain its shape while flexing. The steel belts also aid in the performance of the tires. The tread and sidewalls protects the belts, and provides shape and structure to the tire. The tire beads are wrapped steel chords that hold the tire to the wheel rim.
The Most Common Tread Belt Separation
The most common tread belt separation occurs between the steel belt components. To begin with, it is difficult to adhere rubber to steel and therefore, this area is generally the most vulnerable to separation.because it is the weakest area of adhesion. Furthermore, this is the highest area of stress during normal use. Because of centrifugal forces that result from the rotating tire, the belts want to separate. It is therefore important for a manufacturer to insure that proper measures are undertaken during the design and manufacture of a tire to prevent this from occurring.
Some design considerations include, for example, the amount percentage of halobutyl rubber in and the thickness of the inner liner. While most high-end tire manufacturers use inner liners comprised almost 100% of halobutyl rubber, many low end tire manufacturers use smaller percentages as a cost saving measure. Furthermore, thin inner liners can lead to air permeability. As a result, in either or both instances, air can migrate to the belts causing the rubber around the steel belts to corrode and loose adhesion.
Understanding Belt Wedges
Another design consideration is the size and location of belt wedges. A belt wedge is a rubber wedge that is placed between the belts at the belt edges that allows the belt edge to remain relatively flat and level. The larger and more robust the belt wedge, the more likely the tire resists tread belt separation. An example of this was found in the 1998 Firestone Wilderness AT tires. In 1998, Firestone made the tire wedge larger and more robust in the AT Wilderness tires, with the result being a statistically significant better tire failure rate. Despite this and other research demonstrating the effectiveness of belt wedges, there are still some manufacturers who do not use any wedge materials at the belt edge.
Defects and Tire Durability
Various manufacturing defects can greatly affect tire durability. For example, contaminates can significantly affect adhesion. Gloves, shot gun shells, cigarette butts, bottle caps and even time cards have been found in failed tires. In many cases, the lack of adequate bonding is simply a mistake made in the construction of the tire, the vulcanization of the tire, or the use of inappropriate or off spec. materials to make the tire. To understand this phenomenon, one must understand that tires are assembled from the constituent components. When the components are in the “green” state, they are tacky and thus adhere to one another. Once the “green” tire is finished being assembled, then the tire is vulcanized, or cooked under extreme heat and pressure. During the vulcanization process, the various assembled layers of the green tire meld and bond together into a single homogenous unit. There should be no interfaces left. If, because of a lack of tackiness, or air spaces between the components, there is a lack of bonding during the vulcanization process, then that tire is at risk for de-treading.
Another issue affecting tire safety is tire aging. Research has shown that tires greater than six years old should not be used due to oxidative degradation that occurs over time. As early as 1988 and 1989, certain European and Japanese auto manufacturers began to warn consumers about the hazards of aging tires including that tires more than six years old should not be used. While some U.S. auto manufacturers and tire manufacturers have provided warnings, most deny the association of between tire aging and safety hazards.
If you or a loved one have been seriously injured in an accident caused by a potentially defective tire, contact an experienced defective tire lawyer immediately.