The following are diagrams and a glossary of some of the terms you will see on our website relating to tires. They are broken down into the following categories: Tire Component Terms, and Tire Construction/Manufacture Terms.
Tire Component Terms
The diagram on the left exhibits a tire which does not contain an important safety feature called a nylon safety strip or nylon overlay, pictured in the diagram to the right. The older, less sophisticated, and less durable type of construction pictured to the left, unfortunately, is still employed by many domestic and foreign tire manufacturers for tires sold in the U.S. The Bridgestone/Firestone tires (Wilderness AT and ATX brands) which were involved in the largest tire recall in history, did not contain a nylon strip or overlay component, though the component was added to the same tires by Firestone in some other countries to correct problems there before Firestone ultimately recalled the tires that did not contain that component in the United States.
Nylon Safety Strips or Nylon Overlays, as noted above, are an important tire component designed to maintain the integrity of the tire and prevent catastrophic tread separations (see definition below) by decreasing stresses at the steel belt edges. Remarkably, although tire companies have been aware of this technology and its benefits for years, many tires manufactured and sold in the United States still do not contain this component. Notably, almost all tires sold in Europe contain nylon safety strips in some form or another (some tires have a nylon overlay which covers the entire belt structure and provides even more protection against tread separations, and some tires have both components or multiple layers of protection). Although tread separations can occur in otherwise poorly designed or manufactured tires that employ nylon strips or caps, the vast majority of documented tread separations occur in tires that do not employ either component. If you are in the market for new tires, tell your retailer that you will not purchase a tire that does not have this valuable safety component! It is worth the extra couple of bucks per tire.
The Tread is the outermost part of the tire, and is composed of wear resistant compounds consisting of ribs designed for noise suppression and traction and grooves designed for traction, directional control, and cool running. As reflected in the above diagrams, the tread is located above the steel belts. It is important to keep in mind that the tread is a separate component which is attached to the tire’s inner liner and belt package during the tire construction process. If the tread is not attached and bonded properly, it may separate from the rest of the tire during use.
Tread Separation is an almost entirely preventable but all too common phenomenon in which the tread of a tire literally peels away from the inner liner (pictured above – the portion of the tire which holds the air), while the tire is in operation. It is not unusual when this occurs for the inner-liner of the tire to remain inflated, meaning that the driver is suddenly faced with a situation where he or she is driving, often at highway speeds, with one tire that is fully inflated but has no tread. Unfortunately, tread separations under some conditions cause complete loss of control of the vehicle and, ultimately, injuries or fatalities. When a tread separates completely or partially at highway speeds, it can cause the vehicle to lurch to the side as the tread peels away. This is often a sudden and almost always a completely unexpected event. Many drivers are unable to regain control when this occurs. Tread separations could be mostly eliminated if tire companies took greater care in their design and manufacture of tires, such as by inclusion of inexpensive nylon caps and safety strips in all of their tires rather than just in selected brands (see above). Tire companies claim that tread separations are inevitable and that they are not the result of defects in manufacture or design. Do you think that it is normal for the tread of your tire to fall off when the tire appears otherwise safe and you still have legal tread depth left on your tire? Juries around the country who have heard both sides of this argument have found that tread separations are preventable and that manufacturers breach their duty to the consuming public by selling tires that are susceptible to such incidents.
The Sidewalls are the portions of the tire between the beads and the tread compounded of rubber with high flex and weather resistance to control the ride and provide support.
The Shoulder is the upper portion of the sidewall just below the tread edge and affects tire heat behavior and cornering characteristics;
The Bead is a structure composed of high tensile strength steel wire formed into hoops which function as anchors for the plies and hold the tire assembly onto the rim of the wheel;
The Plies are layers of fabric cord extending from bead to bead to reinforce the tire;
The Belts, are narrow layers of coated tire cord or rubber encased steel cords located directly under the tread in the crown of the tire to resist deformation in the footprint (i.e., the tire's contact patch on the road) to restrict the carcass plies, and to increase the puncture resistance of the tire;
The Liner is a thin layer of rubber inside the tire which contains compressed air.
The Chafer consists of narrow strips of material around the outside of the bead that protect the cord against wear and cutting by the rim, distributes flex above the rim, and prevents dirt and moisture from getting into the tire.
Tire Construction/Tire Manufacture Terms
Contrary to popular belief, tire manufacturing is still a very labor intensive process. At almost all steps of the tire building process, workers physically handle the tire and manually put it together. A tire is not a single piece of rubber which is melted and molded into shape. It is a multi-component product in which various parts are put together to a large extent by hand with the assistance of machines. As with all such manufacturing processes, mistakes can occur. It may be an aggravation to purchase a car which turns out to be a lemon, or an electronic item that breaks in the first week. A similarly defective tire can be deadly. As one tire company likes to point out, there’s a lot riding on your tires. What’s more, the so-called “careful inspections” of tires that most tire companies tout as being a safety net for preventing the sale of defective tires often take no more than a matter of seconds, because most tire companies reward workers for moving a maximum number of tires through the final assembly process each day. Would you believe that everything from sandwich wrappers, blue electrical tape, and even live shotgun shells have been found in tires that were sold to the public? It’s true. Tire companies even have a term for it – “foreign material.” When this foreign material gets into a tire, or a worker fails to take the time to find another problem that occurred in the manufacturing process, even a properly engineered tire can wind up costing a consumer life or well-being.
Below are pictures of ”Green Tires,” or tires which have not yet been cured. Workers physically handle these green tires, and place them into molds and other machines to finish them. The picture on the left is a green tire that has not yet been molded into shape. The picture on the right is a green tire which has been stretched and molded to be the basic shape of a finished tire, but which has not yet been cured.
Mixing the elastomers, carbon blacks, and other chemicals to form the rubber compound – this occurs in a large machine called a Banbury Mixer, which is essentially a giant blender. In many tire plants, workers still physically pour large bags of chemicals into the Banbury mixer to create the compound that is then incorporated into tires built that day at the plant. This is a very important process, but again, one that is susceptible to human error. If you forget a pinch of salt or a cup of butter in your cake recipe, your cake may still look fine but not taste good. If a worker forgets to add a bag of anti-degradants (chemicals designed to prevent the breakdown of rubber through exposure to sunlight, heat and oxygen) into the Banbury mixer, the finished tire made with the compound that comes out will look normal, but may fail prematurely;
Fabricating the various fabrics and Coating them with rubber in a calender;
Tubing the rubber treads and sidewalls by extruding the rubber from a tuber;
Assembling all of those components (i.e., the calendered and cut carcasses and belts, and the extruded tread, sidewall, and beads) on a tire building machine – this is hard physical labor, and a mistake at this stage can result in a tire that does not stick together properly after it is used for a while;
Curing the assembled tire under heat and pressure (called vulcanization) – some tire companies or workers use cure times that are too short and cure temperatures that are too hot because they want to build more tires per day;
Inflating the tire; and
Finishing it (which involves trimming, buffing, balancing, and inspecting).
Prior to vulcanization (cure), the rubber components are in their “green” (uncured) state. As stated above, the tire is built or assembled at the tire building machine in the green state. Basically tire building involves the application of plies and other components onto a cylindrical drum or barrel, commencing with the inner liner. Next, the beads are set in place, and the plies are turned up around the beads. In the case of a belted tire, the belts are applied next, followed by the tread and sidewall. Then, the drum is collapsed, and the tire is removed and loaded onto an automatic tire press for vulcanization at high temperatures and pressures.
After cure, the tire is mounted on a rim and permitted to cool while being inflated. Thereafter, it is finished and shipped to a warehouse for distribution – hopefully without any chicken bones lodged inside of it from a tired worker who dropped his lunch (yes, that’s actually happened, and someone was seriously injured as a result).
OTHER TIRE TERMS OF INTEREST
The following is a list of some other tire related terms that are commonly used in connection with tire failure litigation.
Adjustment: A term used by tire companies to describe the allowance given to a customer when his or her tire fails or suffers a noticeable defect before it is worn out. Tire companies know that their tires sometimes contain defects, and every single major manufacturer in this country has an extensive scheme in place to compensate consumers when they have a problem with their tires. While tire companies may be quick to replace without charge a tire that suffers a tread separation but does not cause injury to the consumer, they tend to be much less willing to admit their mistakes when people are injured or killed as a result of defects in their tires.
Aging: Rubber degrades when exposed to heat, oxygen, ozone, and other elements. Tire companies have known this for decades, and most put expensive anti-degradants in their rubber compounds to prevent tires from falling apart due to the effects of aging. These anti-degradant compounds are part of the reason that tires last so much longer now than they did back in the early days of radial tires. Unfortunately some tire companies, especially those which sell less expensive tires, may skimp on these very important ingredients in some of their brands, but fail to warn consumers to throw those tires away regardless of their tread depth (see definition below) when they are more than a few years old. Of course the reason for this is obvious – the tire companies know that consumers would not buy their tires if they could not count on them to hold together until the tread wears out.
Antioxidant: A chemical added to rubber formulas in tires to prevent the potentially catastrophic effects of aging in tires. See definition of “Aging” above.
Belt Wedge: A tire component used by most manufacturers to prevent tread separations. A belt wedge is a piece of rubber inserted inside the tire at the belt edges. It diffuses some of the heat and stress that can otherwise cause the rubber at the edge of the tires to degrade and fail, leading to a tread separation. If the tire company, wanting to save costs or reduce tire weight, does not utilize a sufficient belt wedge, the results can be catastrophic as seen in the Firestone Wilderness AT and ATX tires.
Carbon Black: Very fine, specially structured particles of carbon used in rubber compounds as a reinforcing filler. This is another critical component in tire manufacture. Carbon black is expensive, but it is crucial to the durability of tires to withstand the tremendous heat and other forces that tires are subjected to in normal operation.
Cold Inflation: The pressure in a tire which has been driven less than one mile or has been standing for three hours or more. Tire companies recommend that you check your tire inflation when your tires are cold.
Compounding: Refers to the mixture of ingredients that go into the rubber used in a tire. These ingredients largely determine how well the tire is able to withstand heat, punctures, oxygen degradation, and the other forces which can cause a tire to fail.
Cure: Another term for tire vulcanization – the application of heat and pressure to the green tire to complete its construction.
Green Tire: A tire which has not been vulcanized or cured.
Load Range: A term referring to the load limit of your tires.
Mag: Speciality wheels such as pure racing wheels contain magnesium, thus the term “mag wheels.” Ironically, most commercially available mag wheels contain little or no magnesium, due to its cost. With the popularity of large multi-piece rims in use in more and more passenger cars, and the growing market for cheaper alternatives to expensive custom rims, the incidence of rim failures is vastly increasing. This is likely to be an unfortunate new cause of preventable injuries and fatalities in years to come, as rim manufacturers produce expensive looking rims that are poorly constructed.
NHTSA: Acronym for the National Highway Traffic Safety Administration. NHTSA conducts investigations into manufacturers who have a large number of tread separations in their tires. But do not be fooled by inaction or the lack of an investigation on the part of NHTSA into any particular tire brand or manufacturer generally – the government entity is poorly funded, and is often misled by tire companies that skew their adjustment (see definition above) data to make it appear as though they have low tire failure rates.
Out-of Round: A wheel or tire defect in which the wheel or tire is not “perfectly” round. This usually results from a mistake or engineering problem in the tire manufacturing process.
Overinflation: The inflation of a tire above its recommended pressure to achieve better gas mileage or performance.
Oversteer: A cornering condition where rear tires operate at greater slip angle than the front tires. All vehicles are designed to be understeer vehicles, so that driver steering input results in predictable vehicle response. When a vehicle suffers a tread separation, some vehicle models become oversteer vehicles, making them very difficult to control. The Ford Explorer was particularly susceptible to this phenomenon, partly explaining the high incidence of loss of control when tread separations occur on that vehicle. A common characteristic of oversteer is that the rear of the vehicle “fishtails” and spins out or rolls over as the driver attempts to steer the vehicle.
PSI: Pounds per square inch. The typical measure for tire inflation.
Rim Flange: The outermost edge of a wheel’s rim to which clip weights are attached. Tire companies often claim that “rim flange grooving” – a condition where grooving can be observed on a used rim flange after an accident involving a failed tire – suggests that a tire was operated overloaded or underinflated. This is a favorite defense of the tire manufacturers when they are sued for defective products. In reality, the defense is pure fiction. Rim flange grooving appears on virtually all rims that are used, whether the tires that were placed on those rims were properly maintained or not. Attempts to measure the difference between “normal” rim flange grooving and abusive rim flange grooving are so subjective that experts in the industry compare it to judging an ice skating competition. Watch out for the French judge!
Rolling Resistance: The force required to roll a loaded tire. Tire companies seek to reduce the rolling resistance of their tires in order to improve gas mileage on vehicles employing the tires. This is especially true for tire manufacturers who supply original equipment tires to vehicle manufacturers for sale with the vehicle. Vehicle manufacturers sometimes demand better rolling resistance from their tire manufacturer suppliers so that they can claim higher mileage ratings on their vehicles. Unfortunately, tire companies sometimes take out crucial components of their tires to improve rolling resistance in order to meet the standards demanded by their customers. This has been linked to the problem that led to the massive Firestone recall.
Tread Depth: The distance from the tread surface to the bottom of the grooves. Most states require a minimum tread depth of 2/32 of an inch. Many tire failures that result in litigation involve tires with more than adequate tread depth, meaning that the consumer had no reason to believe that their tire needed to be replaced.
Tread Life: The length of service in miles anticipated (often warranted) by the tire’s manufacturer before the tread depth will be so low that the tire needs to be replaced. A “40,000 mile tire” is expected to be able to travel approximately 40,000 miles before its tread is worn out. Remarkably, some tire companies in tread separation cases, such as Cooper Tire & Rubber Company, deny that consumers should expect tires that have useful tread life remaining to stay in one piece, claiming that consumers should expect that their tire may suffer a tread separation under some circumstances even when plenty of tread depth (see above) and tread life remains. Perhaps tire companies should tell you that before you buy their tires. Of course, if they did, would you buy their tires, or would you buy the tires of a company that stands behind their product and tells you that you should expect that the tire will wear out before it falls apart?
Wires: Brass plated steel wires are used in steel belted radials. The term “steel belts” is somewhat of a misnomer, because the belts are actually comprised of steel wires wrapped together to form a belt structure.