I. General Information
Tires that fail in road operation can either fail in the sidewall or experience a tread separation. A sidewall failure is often called a “blowout,” and it is typically manifested by a hole in the sidewall. A tread separation usually refers to a separation of the tread from the carcass of the tire - usually between the two steel belts. In other words, the tread and outmost steel belt become detached from the lower steel belt and the rest of the tire carcass. This may occur in whole or in part.
Bead failures generally occur during the mounting of a tire and usually result in injuries to the individual mounting the tire. The bead is the portion of the tire that comes in contact with the rim of the wheel. If the bead breaks during the mounting process, the resulting injury is usually severe.
One of the most common modes of tire failure is tread separation which occurs when the plies of a tire separate from one another. Usually, the tread (with or without attached plies) separates from the carcass or inner plies, exposing the inner liner, belts, and cords. As used in this context, the ply includes one of the steel belts encased in a rubber compound.
Tires are built in layers on a tire building machine while the rubber layers and rubber coated fabrics and belts are in an uncured or “green” state. The fully assembled tire (with all components in their proper places) is then subjected to high temperature and pressure, over time, to cure or vulcanize the assembly. It is this vulcanization process which gives the tire its desired physical properties and bonds the multiple layers or plies of rubber together (both mechanically and chemically) so that they can function as a unit.
Figure 1 is a diagram of a typical component of a tire.
Although the incorporation of steel belts into the steel belted radial tire offers the advantages of additional impact and puncture resistance, it also presents a unique design problem. The rubber compounds routinely used in the manufacture of steel belted tires will not adhere to the steel wires used to make the steel belts. In order to gain proper adhesion, manufacturers must coat the steel wires (usually with brass) before incorporating them into a tire’s construction. However, the coated steel continues to act like steel, and the rubber continues to act like rubber. Therefore, there is a difference in the flexibility of these components of the tire which creates a potential for tread separations in all steel belted radial tires. This potential increases under various operating conditions–most notably load and, to some extent, high speeds.
Given the inherent tendency of all steel belted radial tires to separate beginning at the belt edges on the shoulders of the tire, it is imperative that the tire manufacturer incorporate appropriate countermeasures in the design of the tire to reduce this tendency. It is generally acknowledged that the shoulder of the tire is the location in the tire that develops the highest stresses and heat buildup. Various mechanical and chemical solutions have been developed to reduce the heat, protect against the effects of aging of the polymer materials and diffuse the stresses.
One of the most commonly employed devices to diffuse the stress that can lead to tread separation is the incorporation of an adequate and robust belt wedge placed between the outer and inner steel belts at the belt edge. This wedge is generally triangular in shape and serves both to reduce heat and to diffuse stress. Unfortunately, some tires are still made without a belt wedge.
Figure 2 illustrates tires with and without wedges
Perhaps the most effective means of dealing with the inherent tendency of steel belted radial tires to separate is the use of a nylon cap or nylon edge strips placed on top of the outer steel belt. A full nylon cap or nylon cap ply acts as a tourniquet to restrain the movement of the belts at the shoulder edges. It has the added advantage of diffusing stresses. According to the original patent literature, the nylon cap or strip serves the purpose of restraining the tire during high speed operation to reduce or contain the “standing wave” that develops during high speed operation through centrifugal force. However, the cap strips or plies have also been found to be effective in non-speed rated tires to prevent ordinary separations. U.S. manufactures also acknowledge, at least through practice, that nylon caps or strips are effective in reducing separations occasioned by load, and most load rated tires are now using this technology. Cap plies or strips have been used in Europe for decades.
||Figures 3, 4 and 5 illustrate nylon caps and their placement in the tire.
Another cause of tread separations is the use of permeable inner liner material. The inner liner is the material that forms the chamber that holds the air in a tire. Numerous studies have confirmed that, by creating an impermeable inner liner, the flow of air and moisture throughout the structure of the tire can be significantly reduced to guard against the oxidation of the polymers and steel components that may degrade to the extent that a separation occurs. The permeability of the inner liner is a direct function of the components of the rubber compound that comprise the inner liner. Various butyl rubbers have been employed, and it is generally conceded that the higher the halobutyl content of the inner liner material, the more impervious the inner liner becomes. Halobutyl rubbers are expensive and hence the halobutyl content of the inner liner is often diluted to reduce the costs of manufacture.
|Often in tire litigation, tire manufacturers point to the age of the tire as a factor in the failure. It should be noted, however, that the consumer receives no information relating to the age of the tire, and few jurors could read a DOT number (which contains the date of manufacture), particularly one placed on the axle side of the tire. Even if the age of the tire could be readily ascertained, no manufacturer, either in printed literature or in sidewall warnings, cautions against the use of an older tire. Instead, the Rubber Manufacturer’s Association measures the useful life of a tire by tread wear and adopts the standard of various regulatory schemes which state that a tire is deemed worn out when the tread depth measures 2/32 of an inch.
||For the first time, the Ford/Firestone recall litigation has shown that tread separations tend to occur later in the life of a tire, generally after the third year from manufacture. Increased resistence to tread wear in newer tread compounds dictates the importance of chemical components in the rubber that surrounds the steel belts known as “belt skim stocks” to guard against the natural effects of aging, heat and flexion. All good belt skim stock compounds contain an effective antioxidant chemical. Because some air and moisture will permeate the inner liner and circulate throughout the tire’s structures, it becomes vitally important to ward off premature oxidation of the polymers in the belt skim stock. Like halobutyl rubbers, antioxidant chemicals are expensive, and the reduction or elimination of antioxidants in belt skim stocks are convenient, cost reduction measures employed by some manufacturers
In addition to the design causes for tread separations, there are dozens of other causes that may arise during the manufacturing process. While the list of potential manufacturing defects is virtually endless, among the most common are the introduction of contaminants during the tire building process, moisture affecting the adhesive bond of the rubber surfaces or corrosion of the steel belt wires, use of dry or blooming stock, excessive use of solvents, misalignment or misplacement of steel belts, nylon cap strips or other tire components, the reuse of rejected rubber stocks, and under cure or over cure of the tire during vulcanization.
Contaminants may be of a subtle or blatant variety. Since a tire in its unvulcanized state is inherently sticky or tacky, dust or airborne contaminates may adhere to the sticky surfaces and prevent a complete chemical and mechanical bond of the rubber surfaces leading to a separation. Many tire building rooms of manufacturers are still not air conditioned. Therefore, any airborne contamination or the lack of factory cleanliness may permit the introduction of dust, dirt, floor debris, or other foreign objects into the finished tires. One of the plants of a prominent U.S. manufacturer was populated by cats and other animals leading to severe contamination problems. Among the more shocking items found in finished tires have been gloves, nails, screws, electrical tape, candy or other food wrappings, a live shotgun shell, and even chicken bones.
Moisture introduced during the building process may affect adhesion or cause the steel wires forming the steel belts to corrode. Moisture sources include leading roofs over tire building area, pipe drips or even excessive sweating of tire workers. Improper handling of the steel belt wires may lead to corrosion of the wires themselves and premature tread separations.
The use of dry or blooming rubber compounds may also lead to a lack of good adhesion of the rubber surfaces of a tire. Some rubber compounds, if not used relatively quickly from the time the compound is adhered to the steel belt wires, will begin to cure in atmospheric conditions. A partially cured stock will not properly bond to the adjacent rubber compounds. Blooming is a condition in which one or more of the ingredients of a rubber compound no longer remains dissolved or homogeniously mixed in the rubber compound and migrates to the surface. It is this migration to the surface and the resultant layer which forms there which is called “bloom.” Since the skim stock often contains a high sulphur level, sulphur is the most common ingredient to bloom out preventing the appropriate chemical reactions (called cross-linking) during vulcanization and thus insufficient adhesion of the compound surfaces.
One of the means available to tire builders to deal with aged or dry stock is the use of solvents. Most manufacturers have strict rules relating to the use of solvents because solvents are petroleum based products which, themselves, can degrade the rubber and adversely affect its physical properties. In addition, if an excessive amount of solvent is used, it can become entrapped between two layers or rubber (or two separate components of the tire) resulting in wet surfaces being sealed into the tire, which, again, impacts adhesion.
Rubber compounds do not always conform to the manufacturer’s specifications, and the testing lab may, therefore, reject a particular batch of a given rubber compound. The rejected compound is often mixed into a new batch of the same compound which is up to specification. This combination of a rejected batch with a proper batch may result in a compound with an increased cure rate (called scorch rate) or a compound with too much or too little of a particular ingredient which prevents proper fusing of that compound with another.
Sidewall Zipper Failures
Injuries to tire installers and bystanders often occur when the sidewall of the tire bursts or explodes during the inflation process. The pattern of the rupture often resembles an open zipper - thus the phrase “sidewall zipper failure.”
Prior to inflation, there generally are no visual signs of stress in the sidewall and no outward indication that the tire may experience failure during normal servicing. The deflation of the tire (either in road operation or in a static condition) may, however, cause such stress and lead to a catastrophic blowout when the tire is re-inflated. One particular United States manufacturer seems to have a higher incidence of zipper failures because of its sidewall design and manufacture, although the condition is also known to occur in the case of retreads (where the weakness in the sidewall went undetected during the retread operation).
Though zipper failures are a recognized risk in the tire industry, the response of the manufacturers has been to issue warnings, rather than to make tires less susceptible to anticipated stresses.
Multi-Piece and Split Rim Explosions
Multi-piece wheels or rims have frequently resulted in serious injury or death to tire mounters employed in service stations and tire stores, which is why they are often referred to as “widow makers.” Multi-piece rims are available in numerous configurations or designs, but all are potentially life threatening. Though the Occupational Safety and Health Administration (OSHA) sought to ban multi-piece rims altogether, the tire and wheel industry was successful in avoiding a ban by sponsoring a program of public education in the workplace. Posters designed for the guidance of workers are now prominently displayed in most service stations and tire stores, but the net result of the educational campaign has been to shift liability from the tire and wheel manufacturers to local businesses, employers, and the injured employees.
Although OSHA guidelines require, among other things, the use of a safety cage during the tire mounting operation, accidents still occur after the wheel is removed from the safety cage, for example when it explodes as it is being mounted on the vehicle. The warnings (which are part of the educational program) are not an adequate substitute for a safer design. The single-piece wheel has been available for all tires for almost 40 years. Product liability lawsuits resulting from explosions of the multi-piece rims may hasten their removal from the marketplace.
Bead Hang-Ups and Wheel/Tire Mismatch
The bead is the portion of the tire which comes into direct contact with the wheel. It is composed of high tensile strength steel formed into loops which function as an anchor for the plies and hold the tire assembly onto the rim of the wheel. It is formed during the manufacturing process through production of a bead bundle made up of a series of wires which are overlapped and spliced. Most tire manufacturers use a .037 inch weftless bead configuration in passenger and light truck tires.
Bead failure generally occurs at the splice of the bead bundle, and a separation or fracture of the bead may occur during the inflation process at pressures as low as 38 psi (pounds per square inch). Historically, bead failures have been prevalent in tires designed to save space in the storage compartment or truck of a vehicle, i.e., the so called “space-saver” spares.
During the development of tires designed to be used only as spares and only for short distance driving, manufacturers learned that bead strength could be greatly increased by utilizing a continuous bead construction instead of the traditional spliced construction. Although the continuous bead discovery was made over 20 years ago, splicing is still the design of choice employed by the vast majority of U.S. tire manufacturers because, quite simply, it is cheaper.
Bead failures often occur during the inflation and mounting operation, and the resulting “explosion” is often fatal and almost always serious. This is so because the tire contains compressed air which has enough stored energy to lift a man into the air. During the mounting operation, the bead may become hung up on a portion of the rim, thereby stressing the entire bead bundle. When the bead fractures (usually at the splice joint), and the low pressure explosion occurs, the trajectory of the tire and rim frequently causes amputation of limbs, the crushing of facial bones, or permanent brain damage. These bead hang up situations have been documented in patent literature, litigation reports, and industry articles since the early 1950's.
The splice construction and the bead hang up problems were greatly exacerbated by the introduction of the 16.5 inch rim. Prior to the introduction of the 16.5 inch wheel, tires of one size would not fit on wheel rims of a different size, so an individual attempting to mount a tire on the wrong sized rim would immediately realize his mistake before an injury could occur. Unfortunately, the introduction of the 16.5 inch rim changed all that. A 16 inch tire can be fitted onto a 16.5 inch rim without significant effort. However, such a mismatch will almost always result in a bead hang up and the potential for an explosion.
While bead failure explosions most commonly involve the .037 weftless bead configuration, there are documented cases involving the .051 weftless, Michelin cable and single-strand bead configurations. As noted above, those cases are most often seen where the tire size and rim are mismatched, but there have been fractures where the tire and rim are of the same size. In either case, the failure almost always occurs at the splice joint.
Though exceedingly rare, tire examiners and experts today occasionally see tire failures resulting from ozone cracking (also known as “ozonolysis”). Ozone cracking is characterized by the formation of small cracks or fissures on the surface of the rubber which run perpendicular to the direction of strain.
Atmospheric ozone is a natural enemy of natural rubber compounds. It creates such marked changes in the properties of natural rubber that oxidation itself is considered a chemical modification of the polymer. At ambient temperatures, oxidation in air is a slow process. At higher temperatures, as in warmer climates, the process is speeded up. At any rate, the effects of the chemical changes are cumulative over time, and since the cracks are perpendicular to the direction of strain, ozone cracking can cause rapid deterioration of tire sidewalls in some areas.
Most rubber compound from which most tries on the market today are made include an antiozonant which protects the polymer against the harmful effects of atmospheric ozone. Furthermore, the best UV absorber, carbon black, is used in substantial quantities in most high quality rubber articles, and some compounders nowadays actually double the quantity of antiozonants in high-quality black carcass compounds used in tire construction to increase resistance to UV-induced ozonation and oxidation. Therefore, any ozone cracking in a tire of today’s manufacture is almost always the result of negligence in the manufacturing process - specifically the failure to include antiozonants in the rubber compound.
High Speed Spin-Off Failures
A high speed spin-off failure is a tread separation that occurs in unusual operating conditions. It is almost never seen in vehicles of more recent manufacture, but, when it does occur, it is usually restricted to snowy environments.
This type of failure may occur when one of the two rear wheels is stationary and the other wheel is able to spin without restraint, as on ice. The high centrifugal force of the freely spinning wheel disintegrates the tire. This type of failure is, more often than not, the result of a design defect in the tire or vehicle.
Cases involving a hole in the sidewall of a tire should be reviewed with great caution. Generally a sidewall failure is caused by severe underinflation of the tire during normal operating conditions or contact between the sidewall and a sharp object.
A sidewall hole must be distinguished from a radial split that runs from one bead to the other and completely across the crown of the remaining carcass. Such a finding is not unusual in a tread separation case and generally results from the tremendous forces and impacts during the accident sequence, i.e. it did not cause the tire failure, but rather resulted from it.
Manufacturer Cost and Weight Controls
Perhaps more so than in any other product liability context, a substantial body of evidence exists that many major tire manufacturers have undergone cost reduction programs in which arguably vital tire components have been “designed out” of tires altogether or known tread separation counter-measures have been reduced or made less effective in order to protect the bottom line. For example, tire manufacturers have been known to reduce or eliminate butyl content in skim stock, to reduce belt wedge gauge or remove wedges altogether from their tire designs, and to make numerous other design changes which have the practical effect of making tread separations more likely to occur. Likewise, quality control programs within tire plants can be expensive, and often evidence can be developed that procedures in place at the particular plant where a tire was manufactured were inadequate or not followed during the relevant time frame. The tire industry is highly competitive, especially in the low to moderate priced tire market, so even extremely minor cost reductions can make the difference between a cost competitive model, and one that is passed over by consumers or vehicle manufacturers in favor of a seemingly identical but cheaper alternative.
Tire manufacturers have also been known to reduce or eliminate design components of tires in order to reduce overall tire weight at the behest of vehicle manufacturers or to make their tires more attractive to vehicle manufacturers for use as original equipment. It is a well known fact that a lighter vehicle will obtain higher gas mileage ratings than the same vehicle with more weight. Vehicle manufacturers, faced with both government standards and consumer pressure for better fuel consumption may consequently consider a tire’s weight among the factors for selecting manufacturers and brands for use as original equipment on their vehicles. Occasionally, vehicle manufacturers will even expressly request weight reduction from their tire suppliers. As a practical matter, reducing the weight of the tires means taking some components out, or reducing the size of components that may be vital to the integrity of the tire. While tire manufacturers will claim that such measures do not affect the safety of their tires, there is substantial evidence to the contrary in specific contexts.
Determining which tires may have been subject to these cost reduction or weight reduction programs can be especially challenging in tire litigation; yet it is fundamentally important to developing one’s case. While this type of information is no substitute for competent expert testimony regarding the cause of failure of any particular tire, it can go a long way in demonstrating to a jury a manufacturer’s motivations in making the tire the way it did, and also in establishing a basis for punitive damages.
In virtually every tire case, the tire manufacturer will contend that, at some point during the operating life of the tire, the tire was operated either underinflated or overloaded or a combination of the two. This condition is called “overdeflection.” The contention will be advanced that it matters not whether the overdeflection was caused by underinflation or overloading, though studies have shown that load is far more important than inflation pressures. The manufacturer will be unable to point to any scientific experiments or literature standing for the proposition that overdeflection causes tread separations, though texts, articles and industry publications treat the cause and effect between overdeflection and tread separations as a given.
Logic dictates, and plaintiff’s experts will testify, that no such relationship exists except perhaps in the most extreme conditions such as run flat operation of a tire. Overdeflected operation should result in a sidewall failure, rather than a tread separation, because the sidewall of the tire excessively deflects through both overload and underinflation. Excessive flexing gives rise to fatigue failures in the polyester cords leading to blowouts.
The “evidence” of overdeflected operation cited by defense experts will include “rim flange grooving”, uneven tread wear, sidewall cracking, and inner liner discoloration. Generally, none of these findings will be present in the tire except for “rim flange grooving.” Rim flange grooving is allegedly the pressure set caused by abrasion of the tire in the bead and chafer area of the tire (the part that comes in contact with the rim). All tires, however, will develop some “grooving” even when properly inflated and maintained. Accordingly, the testimony of the defense experts becomes a matter of degree. The most usually employed defense experts will admit that any testimony about rim flange grooving is subjective.
Running a close second to claims of overdeflected operation of the tire is the defense of impact damage. Defense experts almost universally assert that, at some time during the operating life of the tire, the tire impacted an object that caused damage to the tire’s internal structures. It is often claimed that the impact may have occurred more than 3000 miles before the actual tread separation. Of course, no expert can define the object impacted, the shape of the object, the speed of the vehicle at the time of impact, or the circumstances of the impact.
Typically the findings in the tire used to support the conclusion of impact damage are the same findings that would result from a design or manufacturing defect in the tire. A polishing of two surfaces in the tire does indicate abrasion wear in the course of a separation failure, but it will be claimed that the polishing proves that the tire was impacted. The impact finding is as vague as rim flange grooving, and it will be conceded that there will not necessarily be a mark on the tread where the impact occurred. Conveniently, defense experts often testify that the impact occurred at the portion of the tread that was not recovered at the accident scene. In actuality, true impact failures are extraordinarily rare, and the people assigned to the manufacturer’s adjustment centers will so testify.
Aside from challenging the manner in which impact damage can be established, one of the ways to combat the impact defense is to demonstrate the absurd nature of the tire industries’ expectations as to what a consumer will do after an impact. The more prominent of the defense experts will testify that the industry expects a driver, upon hitting a pot hole with sufficient force to shake the frame of the vehicle, to stop the car and make an immediate visual inspection of the tire. Whether the driver sees evidence of damage to the tire or not, the industry then expects that he or she will take the tire to a service station and have the tire dismounted from the rim so that a close inspection can be made of the inner liner. Even if that inspection shows no breaks or damage, the consumer should still carefully watch the tire for the next 1000 miles of operation for signs of a separation that would be manifested by a bulge or bubble on the tread of the tire. Who really does that? It is likely that most jurors would not think to follow that rigorous procedure upon hitting a pothole.
In any case where a patch is found in a tire, the manufacturer will contend that the repair was improper. The recommended procedure for repair of a puncture is the use of a plug and a patch. While other methods will also suffice, any deviation from the recommendations of the Rubber Manufacturers Association will give rise to a claimed defense.
As with the case of an underinflated tire, an improper repair should result in the loss of air pressure and ultimately give rise to a sidewall failure, not a tread separation.
Punctures are a manufacturer’s delight in the defense of tire litigation. Where the penetrating object (nail, screw) remains in the tire, the manufacturer will assert that air escaped from the inner liner into the body of the tire causing a tread separation. The fact that a tire may have a sealed puncture on one side of the tire and the separation initiating the failure occurred on the other side, is explained by the manufacturers as a result of a condition known as “intracarcass pressurizaton.” The contention is that all tires have some degree of pressurization that runs throughout the tire and that air will escape in one location and then the pressure will be exerted in other locations to initiate separations. This is an illogical argument, but it has worked for years. The concept that air will escape through the puncture (i.e., the path of least resistance) and the tire will go flat is ignored. Instead, the jury is asked to believe that the escaping air will take a right angle through surfaces that are chemically and mechanically bonded together, giving rise to a separation at some location other than the puncture site. This position is taken even in cases of a partial tread separation where the tread remains attached to the carcass at the point of the puncture. A good plaintiff’s tire expert can explain the absurdity of this assertion.
Before the rash of SUV rollover accidents following tire disablement, the most dangerous defense was the contention of the tire manufacturers that, regardless of the mode of tire failure, no driver should lose control of the vehicle in the event of a tire disablement. Routinely the contention was made, and still is, that a tire failure does not produce sufficient lateral accelerations to cause the vehicle to spin out of control.
It is well established that a vehicle will pull to the side of the tire failure. In other words, a right rear tire failure will result in a pulling of the vehicle to the right, and some driver input will be required to keep the vehicle in its path of travel. The defense accident reconstruction and driver control experts will testify that the driver “over corrected” in response to the tread separation and that it was the over correction which caused the loss of control.
Recent studies have concluded, however, that vehicles experiencing a tire disablement will experience a change in the handling characteristics of the vehicle. SUV’s and sedans alike will change from an understeer vehicle to an oversteer vehicle with tire disablements. Thus, the normal and reasonable reaction of a driver will cause a loss of control.
This issue is no longer the dangerous issue it once was. With over 270 deaths resulting from the Firestone/Ford rollovers and the resulting news coverage, the public has begun to question the traditional belief that the average driver should be able to control a vehicle with a failed tire.