Tire

A tire (in American English and Canadian English) or tyre (in Commonwealth Nations such as UK, Australia, and others excluding Canada) is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground. The word itself may be derived from the word "tie," which refers to the outer steel ring part of a wooden cart wheel that ties the wood segments together (see Etymology below).

The fundamental materials of modern tires are synthetic rubber, natural rubber, fabric and wire, along with other compound chemicals. They consist of a tread and a body. The tread provides traction while the body ensures support. Before rubber was invented, the first versions of tires were simply bands of metal that fitted around wooden wheels in order to prevent wear and tear. Today, the vast majority of tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cords and wires encased in rubber and generally filled with compressed air to form an inflatable cushion. Pneumatic tires are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft.

Etymology and spelling

The Oxford English Dictionary suggests that the word derives from "attire",^[1] while other sources suggest a connection with the verb "to tie".^[2] From the 15th to the 17th centuries the spellings tire and tyre were used without distinction;^[1] but by 1700 tyre had become obsolete and tire remained as the settled spelling.^[1] In the UK, the spelling tyre was revived in the 19th century for pneumatic tires, though many continued to use tire for the iron variety. The Times newspaper in Britain was still using tire as late as 1905.^[3] The 1911 edition of the Encyclopædia Britannica states that "[t]he spelling 'tyre' is not now accepted by the best English authorities, and is unrecognized in the US",^[2] while Fowler's Modern English Usage of 1926 says that "there is nothing to be said for 'tyre', which is etymologically wrong, as well as needlessly divergent from our own [sc. British] older & the present American usage".^[1] However, over the course of the 20th century tyre became established as the standard British spelling.

History

Iron tires

The earliest tires were bands of iron (later steel), placed on wooden wheels, used on carts and wagons. The tire would be heated in a forge fire, placed over the wheel and quenched, causing the metal to contract and fit tightly on the wheel. A skilled worker, known as a wheelwright, carried out this work. The outer ring served to "tie" the wheel segments together for use, providing also a wear-resistant surface to the perimeter of the wheel. So these tires were able to sustain very heavy pressures. The word "tire" thus emerged as a variant spelling to refer to the metal bands used to tie wheels.

Rubber tires

The first practical pneumatic tire was made by John Boyd Dunlop while working as a veterinarian in May Street, Belfast, in 1887 for his son's bicycle, in an effort to prevent the headaches his son had while riding on rough roads (Dunlop's patent was later declared invalid because of prior art by fellow Scot Robert William Thomson). Dunlop is credited with "realizing rubber could withstand the wear and tear of being a tire while retaining its resilience".^[4]

Pneumatic tires are made of a flexible elastomer material, such as rubber, with reinforcing materials such as fabric and wire. Tire companies were first started in the early 20th century, and grew in tandem with the auto industry. Today, over 1 billion tires are produced annually in over 400 tire factories, with the three top tire makers commanding a 60% global market share.

Chronology

• 1844 – Charles Goodyear invents and patents the rubber vulcanization process
• 1846 – Robert William Thomson invents and patents the pneumatic tire
• 1880s – John Boyd Dunlop begins taping pneumatic tires to bicycle wheels^[5]
• 1888 – First commercial pneumatic bicycle tire produced by Dunlop
• 1889 – Dunlop patents the pneumatic tire in the UK
• 1889 – Adolphe Clément sees a Dunlop pneumatic tire in London and acquires the French manufacturing rights for 50,000 francs
• 1890 – Dunlop, and William Harvey Du Cros begin production of pneumatic tires in Ireland; thickened beads, wire retainers, and shaped rims make taping tires to rims unnecessary.^[5]
• 1890 – Bartlett Clincher rim introduced
• 1891 – Dunlop's patent invalidated in favor of Thomson’s
• 1891 – The Michelin brothers patent a removable pneumatic tire, used by Charles Terront to win the world's first long distance cycle race, Paris–Brest–Paris.
• 1892 – Beaded edge tires introduced in the U.S.
• 1893 – Cotton reinforcing cords have appeared^[5]
• 1894 – E.J. Pennington invents the first balloon tire
• 1895 – Michelin introduces pneumatic automobile tires; André Michelin uses corded tires in Paris-Bordeaux-Paris rally:^[5] by 1897, they are standard racing tires^[5]
• 1898 – Schrader valve stem patented
• 1900 – Cord tires introduced by Palmer (England) and BFGoodrich (U.S.)
• 1903 – Paul W. Litchfield of the Goodyear Tire Company granted patent for the first tubeless tire, which was introduced in 1954 by Goodyear on Packards)^[6][7] (Litchfield would go on to become Goodyear's president and board chairman.)
• 1904 – Goodyear and Firestone start producing cord-reinforced tires
• 1904 – Mountable rims introduced, allowing drivers to fix their own flats
• 1906 – First pneumatic aircraft tire
• 1908 – Harvey Firestone invents and patents "no skid" tread for improved traction
• 1908 – Frank Seiberling invents grooved tires with improved road traction
• 1900s  – Tire companies experiment with adding leather, wood, and steel to improve durability^[5]
• 1910 – Silvertown Rubber Company (London) adds carbon black to white rubber, increasing durability: now universal^[5]
• 1919 – Goodyear and Dunlop announce pneumatic truck tires^[8]
• 1923  – First balloon tire, named for larger cross section and lower pressure, introduced by Firestone: debut on the first Chrysler, the 70, in 1924^[5]
• 1929  – Solid automobile tires cease to be used^[5]
• 1937 – BFGoodrich introduces the first commercial synthetic rubber tire
• 1938 – Goodyear introduces the rayon cord tire
• 1946 – Michelin introduces the radial tire
• 1947 – Goodyear introduces first nylon belted tires
• 1947 – BFGoodrich announces the tubeless tire^[9]
• 1963 – Use of polyester cord introduced by Goodyear
• 1965 – Armstrong Rubber introduces the bias belted fiberglass tire
• 1967 – Poly/glass tires introduced by Firestone and Goodyear
• 1968 – United States Department of Transportation (DOT) numbers required on new tires in U.S.
• 1974 – Pirelli introduces the wide (low aspect ratio) radial tire
• 1975 – Michelin very first American-built radial passenger tire ^[10]
• 1977 – Goodyear introduces the first all-season radial tire, the Tiempo
• 1992 – Michelin introduces the first durable silica-filled tire, also known as "green tires".^[11]
• 1998 – Michelin develops tire that’s vertically anchored and unseatable, allowing it to run flat after a loss of pressure,^[12]

For a list of tire companies and the dates they were established, see List of Tire Companies.

Manufacturing

Pneumatic tires are manufactured according to relatively standardized processes and machinery, in around 450 tire factories in the world. Over 1 billion tires are manufactured annually, making the tire industry the majority consumer of natural rubber. In 2015 1.72 billion tires are expected to be sold globally.^[13] Tire factories start with bulk raw materials such as rubber, carbon black, and chemicals and produce numerous specialized components that are assembled and cured. This article describes the components assembled to make a tire, the various materials used, the manufacturing processes and machinery, and the overall business model.

In 2004, $80 billion of tires were sold worldwide,^[14] in 2010 it was $140 billion.^[15]

The top five tire manufacturing companies by revenue are Bridgestone, Michelin, Goodyear, Continental AG and Pirelli.^[16]

Components

A tire carcass is composed of several parts.

Tread

The tread is the part of the tire that comes in contact with the road surface. The portion that is in contact with the road at a given instant in time is the contact patch. The tread is a thick rubber, or rubber/composite compound formulated to provide an appropriate level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, lugs, voids and sipes. Grooves run circumferentially around the tire, and are needed to channel away water. Lugs are that portion of the tread design that contacts the road surface. Voids are spaces between lugs that allow the lugs to flex and evacuate water. Tread patterns feature non-symmetrical (or non-uniform) lug sizes circumferentially in order to minimize noise levels at discrete frequencies. Sipes are valleys cut across the tire, usually perpendicular to the grooves, which allow the water from the grooves to escape to the sides in an effort to prevent hydroplaning.

Treads are often designed to meet specific product marketing positions. High performance tires have small void ratios to provide more rubber in contact with the road for higher traction, but may be compounded with softer rubber that provides better traction, but wears quickly. Mud and snow (M&S) tires are designed with higher void ratios to channel away rain and mud, while providing better gripping performance. Specialized tires will always work better than general/all purpose/all weather tires when being used in the conditions the specialized tires are designed for.

Tread lug

Tread lugs provide the contact surface necessary to provide traction. As the tread lug enters the road contact area, or footprint, it is compressed. As it rotates through the footprint it is deformed circumferentially. As it exits the footprint, it recovers to its original shape. During the deformation and recovery cycle the tire exerts variable forces into the vehicle. These forces are described as Force Variation.

Tread void

Tread voids provide space for the lug to flex and deform as it enters and exits the footprint. Voids also provide channels for rainwater, mud, and snow to be channeled away from the footprint. The void ratio is the void area of the tire divided by the entire tread area. Low void areas have high contact area and therefore higher traction on clean, dry pavement.

Rain groove

The rain groove is a design element of the tread pattern specifically arranged to channel water away from the footprint. Rain grooves are circumferential in most truck tires. Many high performance passenger tires feature rain grooves that are angled from the center toward the sides of the tire. Some tire manufacturers claim that their tread pattern is designed to actively pump water out from under the tire by the action of the tread flexing. This results in a smoother ride in different types of weather.

Sipe

Tread lugs often feature small narrow voids, or sipes, that improve the flexibility of the lug to deform as it traverses the footprint area. This reduces shear stress in the lug and reduces heat build up. Testing of identical siped and unsiped tires showed measurable improvements in snow traction and ice braking performance, however diminishing and extending braking distances on wet and dry pavement by a few feet on siped tires. Off-road Tire enthusiasts have been siping tires for years for greater traction, as many manufacturers now offer already siped off-road-tires.

Wear bar

Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tire has reached its wear limit. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tires are fully worn and should be taken out of service. Most wear bars indicate a remaining tread depth of 1.6 millimetres (0.063 in) and are deemed "worn out" at that point.^[17]

Bead

The bead is that part of the tire that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. The bead fit is tight to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship to the tire is a factor in the handling characteristics of an automobile, because the rim supports the tire's profile.

Sidewall

The sidewall is that part of the tire that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for strength and flexibility. The sidewall transmits the torque applied by the drive axle to the tread in order to create traction. The sidewall, in conjunction with the air inflation, also supports the load of the vehicle. Sidewalls are molded with manufacturer-specific detail, government mandated warning labels, and other consumer information, and sometimes decorative ornamentation, like whitewalls.

Shoulder

The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.

Ply

Plies are layers of relatively inextensible cords embedded in the rubber^[18] to hold its shape by preventing the rubber from stretching in response to the internal pressure. The orientations of the plies plays a large role in the performance of the tire and is one of the main ways that tires are categorized.

Associated components

Several additional components may be required in addition to just the tire to form a functional wheel.

Rim

Tires are mounted to wheels that bolt to the hub. The beads of the tire are held on the wheel's rim largely by the internal tire force from the air pressure. Automotive wheels are typically made from pressed and welded steel, or a composite of lightweight metal alloys, such as aluminum or magnesium. These alloy wheels may be either cast or forged. A decorative hubcap and trim ring may be placed over the wheel.

Inner tube

Almost all bicycle tires, many motorcycle tires, and many tires for large vehicles such as buses, heavy trucks, and tractors are designed for use with inner tubes. Inner tubes are torus-shaped balloons made from an impermeable material, such as soft, elastic synthetic rubber, to prevent air leakage. The inner tubes are inserted into the tire and inflated to retain air pressure.

Large inner tubes, which are large inflatable toruses, can be re-used for other purposes, such as swimming and rafting (see swim ring), tubing (recreation), sledding, and skitching. Purpose-built inflatable toruses are also manufactured for these uses, offering choice of colors, fabric covering, handles, decks, and other accessories, and eliminating the protruding valve stem.

Valve stem

The valve stem is a tube made of metal or rubber, through which the tire is inflated, with a check valve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve on high-performance bicycles. Valve stems usually protrude through the wheel for easy access. They mount directly to the rim, in the case of tubeless tires, or are an integral part of the inner tube. The rubber in valve stems eventually degrades, and, in the case of tubeless tires, replacement of the valve stem at regular intervals or with tire replacement reduces the chance of failure.

Construction types

Bias

Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.

Belted bias

A belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. The plies and belts are at different angles, which improves performance compared to non-belted bias tires. The belts may be cord or steel.

Radial

Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stabilizer belts directly beneath the tread. The belts may be cord or steel. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability and lower grip ability at low speeds.^[19]

Solid

Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types of light industrial vehicles, carts, and trailers. One of the most common applications for solid tires is for material handling equipment (forklifts). Such tires are installed by means of a hydraulic tire press.

Semi-pneumatic

Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-weight, low-cost, puncture proof, and provide cushioning.^[20] These tires often come as a complete assembly with the wheel and even integral ball bearings. They are used on lawn mowers, wheelchairs, and wheelbarrows. They can also be rugged, typically used in industrial applications,^[21] and are designed to not pull off their rim under use.

Tires that are hollow but are not pressurized have also been designed for automotive use, such as the Tweel (a portmanteau of tire and wheel), which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but the interior has special compressible polyurethane springs to contribute to a comfortable ride. Besides the impossibility of going flat, the tires are intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered by low profile tires. They have not yet been delivered for broad market use.

Specifications

Tire pressure monitoring system

Tire pressure monitoring systems (TPMS) are electronic systems that monitor the tire pressures on individual wheels on a vehicle, and alert the driver when the pressure goes below a warning limit. There are several types of designs to monitor tire pressure. Some actually measure the air pressure, and some make indirect measurements, such as gauging when the relative size of the tire changes due to lower air pressure.

Inflation pressure

Tires are specified by the vehicle manufacturer with a recommended inflation pressure, which permits safe operation within the specified load rating and vehicle loading. Most tires are stamped with a maximum pressure rating. For passenger vehicles and light trucks, the tires should be inflated to what the vehicle manufacturer recommends, which is usually located on a decal just inside the driver's door or in the vehicle owners handbook. Tires should not generally be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure.^[22] High performance and dynamic drivers often increase the tire pressure to near the maximum pressure as printed on the sidewall. This is done to sacrifice comfort for performance and safety. It is definitely very dangerous to allow tire pressure to drop below the recommended placard vehicle pressure, although this is commonly done temporarily when driving on sand to reduce chance of bogging. The reason for this is that it increases the amount of tire wall movement as a result of cornering forces. Should a low pressure tire be forced to perform an evasive maneuver, the tire wall will be more pliable than had it been of a higher pressure, and thus it will "roll" under the wheel. This increases the entire roll movement of the car, and diminishes tire contact area on the negative side of the vector. Thus only half the tire is in contact with the road, and the tire may deform to such an extent that the side wall on the positive vector side becomes in contact with the road. The probability of failing in the emergency maneuver is thus increased.

Further, with low tire pressure—due to the side wall being more pliable—the tire will absorb more of the irregular forces from normal driving, and with this constant bending of the side wall as it absorbs the contours of the road, it heats up the tire wall to possibly dangerous temperatures, as well as degrades the steel wire reinforcement; this often leads to side wall blow-outs. In an extreme case of this phenomenon, the vehicle may drive into a pot-hole, or a hard elevation in the road. Due to the low tire pressure, the side wall at the contact area will temporarily collapse, thereby wedging the tire between the wheel and road, resulting in a tire laceration and blow-out, as well as a damaged wheel. High tire pressures are more inclined to keep its shape during any encounter, and will thus transmit the forces of the road to the suspension, rather than being damaged itself. This allows for an increased reaction speed, and "feel" the driver perceives of the road. Modern tire designs allow for minimal tire contact surface deformity during high pressures, and as a result the traditional wear on the center of the tire due to reasonably high pressures is only known to very old or poorly designed tires.

Feathering occurs on the junction between the tire tread and side wall, as a result of too low tire pressures. This is as a result of the inability of the tire to perform appropriately during cornering forces, leading to aberrant and shearing forces on the feathering area. This is due to the tire moving sideways underneath the wheel as the tire pressures are insufficient to transmit the forces to the wheel and suspension. It may be, that very high tire pressures have only two downsides: The sacrifice in comfort; and the increased chance of obtaining a puncture when driving over sharp objects, such as on a newly scraped gravel road. Many individuals have maintained their tire pressures at the maximum side wall printed value (inflated when cold) for the entire lifetime of the tire, with perfect wear until the end. This may be of negative economic value to the rubber and tire companies, as high tire pressures decrease wear, and minimize side wall blow outs.

Many pressure gauges available at fuel stations have been de-calibrated by manhandling and the effect of time, and it is for this reason that vehicle owners should keep a personal pressure gauge with them to validate the correct tire pressure.

During the early stages of tire engineering, and with current basic tires, the tire contact patch is readily reduced by both over-and-under inflation. Over-inflation may increase the wear on the center contact patch, and under-inflation will cause a concave tread, resulting in less center contact. Most modern tires will wear evenly at very high tire pressures, but will degrade prematurely due to low (or even standard) pressures. An increased tire pressure has many benefits, including decreased rolling resistance. It has been found, that an increased tire pressure almost exclusively results in shorter stopping distances, except in some circumstances that may be attributed to the low sample size.^[23] If tire pressure is too low, the tire contact patch is changed more than if it were over-inflated. This decreases rolling resistance, tire flexing, and friction between the road and tire. Under-inflation can lead to tire overheating, premature tread wear, and tread separation in severe cases.^[24]

Tires are not completely impermeable to air, and so lose pressure over time naturally. Some drivers inflate tires with nitrogen, instead of simple air, which is already 78% nitrogen, in an attempt to keep the tires at the proper inflation pressure longer,^[25] though the effectiveness of this is debatable.^[26][27][28]

Load rating

Tires are specified by the manufacturer with a maximum load rating. Loads exceeding the rating can result in unsafe conditions that can lead to steering instability and even rupture. For a table of load ratings, see tire code.

Speed rating

The speed rating denotes the maximum speed at which a tire is designed to be operated. For passenger vehicles these ratings range from 99 to 186 miles per hour (159 to 299 km/h). For a table of speed ratings, see tire code.

Replacing a tire on a vehicle with one with a lower speed rating than originally specified by the vehicle manufacturer may render the insurance invalid.

Service rating

Tires (especially in the U.S.) are often given service ratings, mainly used on bus and truck tires. Some ratings are for long haul, and some for stop-start multi-drop type work. Tires designed to run 500 miles (800 km) or more per day carrying heavy loads require special specifications.

Treadwear rating

The treadwear rating or treadwear grade describes how long the tire manufacturers expect the tire to last. A Course Monitoring Tire (the standard tire that a test tire will be compared to) has a rating of "100". If a manufacturer assigns a treadwear rating of 200 to a new tire, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tire. The "test tires" are all manufacturer-dependent. Brand A's rating of 500 is not necessarily going to give you the same mileage rating as Brand B's tire of the same rating. The testing is non-regulated and can vary greatly. Treadwear ratings are only useful for comparing Brand A's entire lineup against itself. Tread wear, also known as tire wear, is caused by friction between the tire and the road surface. Government legal standards prescribe the minimum allowable tread depth for safe operation.

Rotation

Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn. Furthermore, front-wheel drive vehicles tend to wear the front tires at a greater rate compared to the rears. Tire rotation is the procedure of moving tires to different car positions, such as front-to-rear, in order to even out the wear, thereby extending the life of the tire.

Wheel alignment

When mounted on the vehicle, the wheel and tire may not be perfectly aligned to the direction of travel, and therefore may exhibit irregular wear. If the discrepancy in alignment is large, then the irregular wear will become quite substantial if left uncorrected.

Wheel alignment is the procedure for checking and correcting this condition through adjustment of camber, caster and toe angles. These settings also affect the handling characteristics of the vehicle.

Retread

Tires that are fully worn can be re-manufactured to replace the worn tread. This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread.^[29] Retreading is economical for truck tires because the cost of replacing the tread is less than the price of a new tire. Retreading passenger tires is less economical because the cost of retreading is high compared to the price of new cheap tires, but favorable compared to high-end brands.

Worn tires can be retreaded by two methods, the mold or hot cure method and the pre-cure or cold one. The mold cure method involves the application of raw rubber on the previously buffed and prepared casing, which is later cured in matrices. During the curing period, vulcanization takes place and the raw rubber bonds to the casing, taking the tread shape of the matrix. On the other hand, the pre-cure method involves the application of a ready-made tread band on the buffed and prepared casing, which later is cured in an autoclave so that vulcanization can occur.

During the retreading process, retread technicians must ensure the casing is in the best condition possible, in order to minimize the possibility of a casing failure. Casings with problems such as capped tread, tread separation, unrepairable cuts, corroded belts or sidewall damage, or any run-flat or skidded tires, will be rejected.

In most situations, retread tires can be driven under the same conditions and at the same speeds as new tires with no loss in safety or comfort.^[30] The percentage of retread failures should be about the same as for new tire failures, but many drivers, including truckers, are guilty of not maintaining proper air pressure on a regular basis, and, if a tire is abused (overloaded, underinflated, or mismatched to the other tire on a set of duals), then that tire (new or recapped) will fail.^[31]

Many commercial trucking companies put retreads only on trailers, using only new tires on their steering and drive wheels. This procedure increases the driver's chance of maintaining control in case of problems with a retreaded tire.

Performance characteristics

The interaction of a tire with the pavement is a very complex phenomenon. Many of the details are modeled in Pacejka's Magic Formula. Some are explained below.

Balance

When a wheel and tire rotate, they exert a centrifugal force on the axle that depends on the location of their center of mass and the orientation of their moment of inertia. This is referred to as balance, imbalance, or unbalance. Tires are checked at the point of manufacture for excessive static imbalance and dynamic imbalance using automatic tire balance machines. Tires are checked again in the auto assembly plant or tire retail shop after mounting the tire to the wheel. Assemblies that exhibit excessive imbalance are corrected by applying balance weights to the wheels to counteract the tire/wheel imbalance.

To facilitate proper balancing, most high performance tire manufacturers place red and yellow marks on the sidewalls to enable the best possible match-mounting of the tire/wheel assembly. There are two methods of match-mounting high performance tire to wheel assemblies using these red (uniformity) or yellow (weight) marks.^[32]

Camber thrust

Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch.

Centrifugal growth

A tire rotating at higher speeds tends to develop a larger diameter, due to centrifugal forces that force the tread rubber away from the axis of rotation. This may cause speedometer error. As the tire diameter grows, the tire width decreases. This centrifugal growth can cause rubbing of the tire against the vehicle at high speeds. Motorcycle tires are often designed with reinforcements aimed at minimizing centrifugal growth.

Circle of forces

The circle of forces, traction circle, friction circle, or friction ellipse is a useful way to think about the dynamic interaction between a vehicle's tire and the road surface.

Contact patch

The contact patch, or footprint, of the tire, is the area of the tread that is in contact with the road surface. This area transmits forces between the tire and the road via friction. The length-to-width ratio of the contact patch affects steering and cornering behavior.

Cornering force

Cornering force or side force is the lateral (i.e. parallel to the road surface) force produced by a vehicle tire during cornering.

Dry traction

Dry traction is measure of the tire’s ability to deliver traction, or grip, under dry conditions. Dry traction is a function of the tackiness of the rubber compound.

Force variation

The tire tread and sidewall elements undergo deformation and recovery as they enter and exit the footprint. Since the rubber is elastomeric, it is compressed during this cycle. As the rubber deforms and recovers, it imparts cyclical forces into the vehicle. These variations are collectively referred to as tire uniformity. Tire uniformity is characterized by radial force variation (RFV), lateral force variation (LFV) and tangential force variation. Radial and lateral force variation is measured on a force variation machine at the end of the manufacturing process. Tires outside the specified limits for RFV and LFV are rejected. Geometric parameters, including radial runout, lateral runout, and sidewall bulge, are measured using a tire uniformity machine at the tire factory at the end of the manufacturing process as a quality check. In the late 1990s, Hunter Engineering introduced the GSP9700 Road Force balancer, which is equipped with a load roller similar to the force variation machine used at the factory to grade tire uniformity. This machine can find the best position for the tire on a given wheel so that the over-all assembly is as round as possible.

Load sensitivity

Load sensitivity is the behaviour of tires under load. Conventional pneumatic tires do not behave as classical friction theory would suggest. Namely, the load sensitivity of most real tires in their typical operating range is such that the coefficient of friction decreases as the vertical load, Fz, increases.

Pneumatic trail

Pneumatic trail of a tire is the trail-like effect generated by compliant tires rolling on a hard surface and subject to side loads, as in a turn. More technically, it is the distance that the resultant force of side-slip occurs behind the geometric center of the contact patch.

Relaxation length

Relaxation length is the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value.

Rolling resistance

Rolling resistance is the resistance to rolling caused by deformation of the tire in contact with the road surface. As the tire rolls, tread enters the contact area and is deformed flat to conform to the roadway. The energy required to make the deformation depends on the inflation pressure, rotating speed, and numerous physical properties of the tire structure, such as spring force and stiffness. Tire makers seek lower rolling resistance tire constructions in order to improve fuel economy in cars and especially trucks, where rolling resistance accounts for a high proportion of fuel consumption.

Pneumatic tires also has a much lower rolling resistance than solid tires. Because the internal air pressure acts in all directions, a pneumatic tire is able to "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction of travel, as is the case with a solid (or foam-filled) tire. The difference between the rolling resistance of a pneumatic and solid tire is easily felt when propelling wheelchairs or baby buggies fitted with either type so long as the terrain has a significant roughness in relation to the wheel diameter.

Self aligning torque

Self aligning torque, also known as the aligning torque, SAT or Mz, is the torque that a tire creates as it rolls along that tends to steer it, i.e. rotate it around its vertical axis.

Slip angle

Slip angle or sideslip angle is the angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing (i.e., the angle of the vector sum of wheel translational velocity and sideslip velocity ).

Stopping distance

Performance-oriented tires have a tread pattern and rubber compounds designed to grip the road surface, and so usually have a slightly shorter stopping distance. However, specific braking tests are necessary for data beyond generalizations.

Work load

The work load of a tire is monitored so that it is not put under undue stress, which may lead to its premature failure.^[33] Work load is measured in ton kilometre per hour (TKPH). The measurement's appellation and units are the same. The recent shortage and increasing cost of tires for heavy equipment has made TKPH an important parameter in tire selection and equipment maintenance for the mining industry. For this reason, manufacturers of tires for large earth-moving and mining vehicles assign TKPH ratings to their tires based on their size, construction, tread type, and rubber compound.^[34][35] The rating is based on the weight and speed that the tire can handle without overheating and causing it to deteriorate prematurely. The equivalent measure used in the United States is ton mile per hour (TMPH).

Tread wear

There are several types of abnormal tread wear. Poor wheel alignment can cause excessive wear of the innermost or outermost ribs. Gravel roads, rocky terrain, and other rough terrain causes accelerated wear. Over-inflation above the sidewall maximum can cause excessive wear to the center of the tread. Modern tires have steel belts built in to prevent this. Under-inflation causes excessive wear to the outer ribs. Often, the placard pressure is too low and most tires are under-inflated as a result. Unbalanced wheels can cause uneven tire wear, as the rotation may not be perfectly circular. Tire manufacturers and car companies have mutually established standards for tread wear testing that include measurement parameters for tread loss profile, lug count, and heel-toe wear. See also Work load above.

Wet traction

Wet traction is the tire's traction, or grip, under wet conditions. Wet traction is improved by the tread design's ability to channel water out of the tire footprint and reduce hydroplaning. However, tires with a circular cross-section, such as those found on racing bicycles, when properly inflated have a sufficiently small footprint to not be susceptible to hydroplaning. For such tires, it is observed that fully slick tires will give superior traction on both wet and dry pavement.^[36]

Markings

DOT code

In the United States, the DOT Code is an alphanumeric character sequence molded into the sidewall of the tire for purposes of tire identification. The DOT Code is mandated by the U.S. Department of Transportation. The DOT Code is useful in identifying tires in a product recall.

The DOT Code begins with the letters "DOT" followed by a plant code (two numbers or letters) that identifies where it was manufactured. The last four numbers represent the week and year the tire was built. A three-digit code was used for tires manufactured before the year 2000. For example, 178 means it was manufactured in the 17th week of 8th year of the decade. In this case it means 1988. For tires manufactured in the 1990s, the same code holds true, but there is a little triangle (Δ) after the DOT code. Thus, a tire manufactured in the 17th week of 1998 would have the code 178Δ. In 2000, the code was switched to a 4-digit code. Same rules apply, so for example, 3003 means the tire was manufactured in the 30th week of 2003.

Other numbers are marketing codes used at the manufacturer's discretion.

E-mark

All tires sold for road use in Europe after July 1997 must carry an E-mark. The mark itself is either an upper case "E" or lower case "e" – followed by a number in a circle or rectangle, followed by a further number. An (upper case) "E" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. A (lower case) "e" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of Directive 92/23/EEC. The number in the circle or rectangle denotes the country code of the government that granted the type approval. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tire size and type.

Mold serial number

Tire manufacturers usually embed a mold serial number into the sidewall area of the mold, so that the tire, once molded, can be traced back to the mold of original manufacturer.

Codes

Vehicle applications

Tires are classified into several standard types, based on the type of vehicle they serve. Since the manufacturing process, raw materials, and equipment vary according to the tire type, it is common for tire factories to specialize in one or more tire types. In most markets, factories that manufacture passenger and light truck radial tires are separate and distinct from those that make aircraft or OTR tires.

Passenger vehicles and light truck

High performance

High performance tires are designed for use at higher speeds, and more often, a more "sporty" driving style. They feature a softer rubber compound for improved traction, especially on high speed cornering. The trade off of this softer rubber is shorter tread life.

High performance street tires sometimes sacrifice wet weather handling by having shallower water channels to provide more actual rubber tread surface area for dry weather performance. The ability to provide a high level of performance on both wet and dry pavement varies widely among manufacturers, and even among tire models of the same manufacturer. This is an area of active research and development, as well as marketing.

Mud and snow

Mud and Snow, (or M+S, or M&S), is a designation applied rather arbitrarily by manufacturers for all-season and winter tires designed to provide improved performance under low temperature conditions, compared to summer tires. The tread compound is usually softer than that used in tires for summer conditions, thus providing better grip on ice and snow, but wears more quickly at higher temperatures. Tires may have well above average numbers of sipes in the tread pattern to grip the ice. There are no traction performance requirements which such a tire has to meet; M&S relates to the percentage of tread void area.

Dedicated winter tires will bear the "Mountain/Snowflake Pictograph" if designated as a winter/snow tire by the American Society for Testing & Materials. Winter tires will typically also carry the designation MS, M&S, or the words MUD AND SNOW (but see All-season tires, below).

Some winter tires may be designed to accept the installation of metal studs for additional traction on icy roads. The studs also roughen the ice, thus providing better friction between the ice and the soft rubber in winter tires. Use of studs is regulated in most countries, and even prohibited in some locales due to the increased road wear caused by studs. Typically, studs are never used on heavier vehicles. Studded tires are used in the upper tier classes of ice racing^[37] and rallying.

Other winter tires rely on factors other than studding for traction on ice, e.g. highly porous or hydrophilic rubber that adheres to the wet film on the ice surface.

Some jurisdictions may require snow tires or tire chains on vehicles driven in certain areas during extreme weather conditions.

Mud tires are specialty tires with large, chunky tread patterns designed to bite into muddy surfaces. The large, open design also allows mud to clear quickly from between the lugs. Mud terrain tires also tend to be wider than other tires, to spread the weight of the vehicle over a greater area to prevent the vehicle from sinking too deeply into the mud. However in reasonable amounts of mud and snow, tires should be thinner. Being thinner, the tire will have more pressure on the road surface, thus allowing the tires to penetrate the snow layer and grip harder snow or road surface beneath. This does not compensate when the snow is too deep for such penetration, where the vehicle will sink into the snow and 'snowplow' the snow in front. In this case, wider tires are preferred, as they have a larger contact patch and are better able to 'float' on top of the mud or snow.

All season

The All Season tire classification is a compromise between one developed for use on dry and wet roads during summer and one developed for use under winter conditions. The type of rubber and the tread pattern best suited for use under summer conditions cannot, for technical reasons, give good performance on snow and ice. The all-season tire is a compromise, and is neither an excellent summer tire nor an excellent winter tire. They have, however, become almost ubiquitous as original and replacement equipment on automobiles marketed in the United States, due to their convenience and their adequate performance in most situations. Even so, in other parts of the world, like Germany, it is common to have a designated tire set for winter and summer. All-Season tires are also marked for mud and snow the same as winter tires but rarely with a snowflake. Owing to the compromise with performance during summer, winter performance is usually poorer than a winter tire.

All-terrain

All-terrain tires are typically used on SUVs and light trucks. These tires often have stiffer sidewalls for greater resistance against puncture when traveling off-road, the tread pattern offers wider spacing than all-season tires to remove mud from the tread. Many tires in the all-terrain category are designed primarily for on-road use, particularly all-terrain tires that are originally sold with the vehicle.

Spare

Some vehicles carry a spare tire, already mounted on a wheel, to be used in the event of flat tire or blowout. Minispare, or "space-saver spare" tires are smaller than normal tires to save on trunk/boot space, gas mileage, weight, and cost. Minispares have a short life expectancy and a low speed rating, often below 60 miles per hour (97 km/h).

Run-flat

Several innovative designs have been introduced that permit tires to run safely with no air for a limited range at a limited speed. These tires typically feature strong, load-supporting sidewalls. An infamous example of an alternate run-flat technology has plastic load-bearing inserts attached to the rim instead of the reinforced sidewalls.

A disadvantage is that run-flat tires cannot be repaired if a puncture occurs, this is due to manufacturer's informing the automotive industry that you cannot tell what kind of state the sidewall is in due to the compacted sidewall of rubber.

Heavy duty truck

Heavy duty tires are also referred to as Truck/Bus tires. These are the tire sizes used on vehicles such as commercial freight trucks, dump trucks, and passenger buses. Truck tires are sub-categorized into specialties according to vehicle position such as steering, drive axle, and trailer. Each type is designed with the reinforcements, material compounds, and tread patterns that best optimize the tire performance. A relatively new concept is the use of "Super Singles" or Wide Singles. Generally in a dual configuration, there are 2 tires per position, each between 275 mm-295 mm wide. The Super Single replaces these with a single tire, usually 455 mm wide. This allows for less tread to be contacting the ground and also eliminates 2 sidewalls per position. Along with the weight savings of about 91 kilograms (200 lb) per axle, this enables vehicles using these to improve fuel economy.

Off-the-road (OTR)

The OTR tire classification includes tires for construction vehicles such as wheel loaders, backhoes, graders, trenchers, and the like; as well as large mining trucks. OTR tires can be of either bias or radial construction although the industry is trending toward increasing use of radial. Bias OTR tires are built with a large number of reinforcing plies to withstand severe service conditions and high loads.

Dramatically increasing commodity prices has led to shortages of new tires. As a consequence, multi-million dollar trucks can be idled for lack of tires, costing mines millions of dollars in lost productivity. This has led to a stronger effort to recycle old OTR tires. As of 2008, a new OTR tire can cost up to $50,000; retread tires are sold at half the price of new tires, and last 80% as long.^[38] Retreading an OTR tire is labor intensive. First, the retreading technician must place the old tire in a buffing machine to remove what remains of the old tread; "skiving" follows this, which is the removal, by hand, of material the buffing misses. Next, the technician must inspect the tire, repairing defects. Lastly, the technician fills holes in the tire with rubber, applies a cement gum adhesive, and places the tire on a machine that will apply a new tread.^[39]

Agricultural

The agricultural tire classification includes tires used on farm vehicles, typically tractors and specialty vehicles like harvesters. Driven wheels have very deep, widely spaced lugs to allow the tire to grip soil easily. High flotation tires are used in swampy environments and where soil compaction is a concern, featuring large footprints at low inflation pressures.

Racing

Racing tires are highly specialized according to vehicle and race track conditions. This classification includes tires for drag racing, Auto-x, drifting, Time Attack, Road Racing  – as well as the large-market race tires for Formula One, IndyCar, NASCAR, rallying, MotoGP and the like. Tires are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Racing tires often are engineered to minimum weight targets, so tires for a 500 miles (800 km) race may run only 100 miles (160 km) before a tire change. Some tire makers invest heavily in race tire development as part of the company's marketing strategy and a means of advertising to attract customers.

Racing tires often are not legal for normal highway use.

Industrial

The Industrial tire classification is a bit of a catch-all category and includes pneumatic and non-pneumatic tires for specialty industrial and construction equipment such as skid loaders and fork lift trucks.

Bicycle

This classification includes all forms of bicycle tires, including road racing tires, mountain bike tires, snow tires, and tubular tires, used also with other human-powered vehicles (see Category:Human-powered vehicles).

Aircraft

Aircraft tires are designed to withstand extremely heavy loads for short durations. The number of tires required for aircraft increases with the weight of the plane (because the weight of the airplane is distributed better). Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect. Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 pounds per square inch (14 bar; 1,400 kPa) for airliners, and even higher for business jets. Tests of airline aircraft tires have shown that they are able to sustain pressures of maximum 800 pounds per square inch (55 bar; 5,500 kPa) before bursting. During the test the tires have to be filled with water, instead of helium or nitrogen, which is the common content of aircraft tires, to prevent the test room being blown apart by the energy when the tire bursts.

Aircraft tires also include heat fuses, designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during an aborted takeoff or an emergency landing. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.

The requirement that an inert gas, such as nitrogen, be used instead of air for inflation of tires on certain transport category airplanes was prompted by at least three cases in which the oxygen in air-filled tires combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of an inert gas for tire inflation will eliminate the possibility of a tire explosion.^[40]

Motorcycle

There are many different types of motorcycle tires:

Sport Touring – these tires are generally not used for high cornering loads, but for long straights, good for riding across the country.

Sport Street – these tires are for aggressive street riders that spend most of their time carving corners on public roadways. These tires do not have a long life, but in turn have better traction in high speed cornering. Street and sport street tires have good traction even when cold, but when warmed too much, can actually lose traction as their internal temperature increases.

Track or Slick – these tires are for track days or races. They have more of a triangular form, which in turn gives a larger contact patch while leaned over. These tires are not recommended for the street by manufacturers, and are known to have a shorter life on the street. Due to the triangulation of the tire, there will be less contact patch in the center, causing the tire to develop a flat spot quicker when used to ride on straightaways for long periods of time and have no tread so they lose almost all grip in wet conditions. Racing slicks are also made of a harder rubber compound and do not provide as much traction as street tires until warmed to a higher internal temperature than street tires normally operate at. Most street riding will not put a sufficient amount of friction on the tire to maintain the optimal tire temperature, especially in colder climates and in spring and fall.

Sound and vibration characteristics

The design of treads and the interaction of specific tire types with the roadway surface type produces considerable effect upon sound levels or noise pollution emanating from moving vehicles. These sound intensities increase with higher vehicle speeds.^[41] The acoustic intensity produced varies considerably depending on the tire tread design and the road surface type. There is a study "under development" that aims predict the interior noise due to the vibrations of a rolling tire structurally transmitted to the hub of a vehicle".^[42]

Regulatory bodies

DOT

The United States Department of Transportation (DOT) is the U.S. governmental body authorized by the U.S. Congress to establish and regulate transportation safety in the United States of America.

NHTSA

The National Highway and Traffic Safety Administration (NHTSA) is a U.S. government body within the Department of Transportation tasked with regulating automotive safety in the United States.

UTQG

The Uniform Tire Quality Grading System (UTQG), is a system for comparing the performance of tires, established by the United States National Highway Traffic Safety Administration according to the Code of Federal Regulations 49 CFR 575.104. The UTQG regulation requires labeling of tires for tread wear, traction, and temperature.

T&RA

The Tire and Rim Association (T&RA) is a voluntary U.S. standards organization to promote the interchangeability of tires and rim and allied parts. Of particular interest, they published key tire dimension standards, key rim contour dimension standards, key tire valve dimension standards, and load / inflation standards.

ETRTO

The European Tyre and Rim Technical Organization (ETRTO) is the European standards organization "to establish engineering dimensions, load/pressure characteristics and operating guidelines" .^[43] for tires, rims and valves. It is analogous to T&RA.

JATMA

The Japanese Automobile Tire Manufacturers Association (JATMA) is the Japanese standards organization for tires, rims anbd valves. It is analogous to T&RA and ETRTO.

TREAD Act

The Transportation Recall Enhancement, Accountability and Documentation Act (TREAD Act) is a United States federal law that sets standards for testing and the reporting of information related to products involved with transportation such as cars and tires.

RFID tags

Radio Frequency IDentification tags (RFID) are passive transponders affixed to the inside of the tire for purposes of automatic identification. Tags are encoded with various types of manufacturing data, including the manufacturer’s name, location of manufacture, tire type, manufacturing date, and in some cases test data. RFID transponders can remotely read this data automatically. RFID tags are used by auto assemblers to identify tires at the point of assembly to the vehicle. Fleet operators utilize RFID as part of tire maintenance operations.

CCC (China Compulsory Certification) is a mandatory certification system concerning product safety in China that went into effect in August 2002. Before CCC, there were two certification systems in China: CCIB and CCEE. With China's entrance into the WTO, these two systems were unified into the CCC certification system. After the termination of a one-year grace period in August 2003, the system became compulsory.The CCC certification system is operated by the State General Administration for Quality Supervision and Inspection and Quarantine of the People's Republic of China (AQSIQ) and the Certification and Accreditation Administration of the People's Republic of China (CNCA).

Safety

Proper vehicle safety requires specific attention to inflation pressure, tread depth, and general condition of the tires. Over-inflated tires run the risk of explosive decompression (they may pop). On the other hand, under-inflated tires have a higher rolling resistance and suffer from overheating and rapid tread wear particularly on the edges of the tread. Excessive tire wear will reduce steering and braking response, and tires worn down past their safety margins and into the casing run the very real risk of rupturing. Also, certain combinations of cross ply and radial tires on different wheels of the same vehicle can lead to vehicle instability, and may also be illegal. Vehicle and tire manufacturers provide owners' manuals with instructions on how to check and maintain tires.

Flat

A flat tire occurs when a tire deflates. This can occur as a result of normal wear-and-tear, a leak, or more serious damage. A tire that has lost sufficient pressure will impair the stability of the vehicle and may damage the tire further if it is driven in this condition. The tire should be changed and/or repaired before it becomes completely flat. Continuing to drive a vehicle with a flat tire will damage the tire beyond repair, possibly damage the rim and vehicle, and put the occupants and other vehicles in danger. A flat tire or low-pressure tire should be considered an emergency situation, requiring immediate attention. Some tires, known as "run-flat tires", have either extremely stiff sidewalls or a resilient filler to allow driving a limited distance while flat, usually at reduced speed, without permanent damage or hazard.

A modern radial tire may not be visibly distorted even with dangerously low inflation pressure. (This is especially true of tires with a low aspect ratio, sometimes known as "low profile" tires.) Thus maintenance of adequate tire pressure can have important safety implications despite the fact that most car owners neglect it. Tire designers have tried to make new tires fail-safe so that the failure of the operator to maintain the tire pressure won't cause a major safety concern, but there are limitations on this.

Hydroplaning (or aquaplaning)

Hydroplaning, also known as aquaplaning, is the condition where a layer of water builds up between the tire and road surface. Hydroplaning occurs when the tread pattern cannot channel away enough water at an adequate rate to ensure a semi-dry footprint area. When hydroplaning occurs, the tire effectively "floats" above the road surface on a cushion of water – and loses traction, braking and steering, creating a very unsafe driving condition. When hydroplaning occurs, there is considerably less responsiveness of the steering wheel. The correction of this unsafe condition is to gradually reduce speed, by merely lifting off the accelerator/gas pedal.

Hydroplaning becomes more prevalent with wider tires (because of the lower weight per contact area) and especially at higher speeds; it is of virtually no concern to bicycle tires under normal riding conditions largely because of the lower speeds. The chance of car hydroplaning is also minimal at bicycle speeds as the weight per contact area of car tires is not much lower if any than bicycle tires.

Dangers of aged tires

Research and tests show that as tires age, they begin to dry out and become potentially dangerous, even if unused. Aged tires may appear to have similar properties to newly manufactured tires, but rubber degrades over time, and once the vehicle is traveling at high speeds (i.e. on a freeway) the tread could peel off, leading to severe loss of control. In tropical climates, such as Singapore, tires degrade sooner than in temperate climates, and more care should be taken in these climates to ensure that tires do not fail. Also, tires on seldom-used trailers are at the greatest risk of age-failure, but some tires are built to withstand idleness, usually with nylon reinforcement.

Many automakers recommend replacing tires after six years, and several tire manufacturers (Bridgestone, Michelin) have called for tires to be removed from service 10 years after the date of manufacture. However, an investigative report by Brian Ross on ABC's 20/20 news magazine found that many major retailers such as Goodyear, Wal-Mart, and Sears were selling tires that had been produced six or more years ago. Currently, no law for aged tires exists in the United States.^[44][45]

Scrap tires and environmental issues

Once tires are discarded, they are considered scrap tires. Scrap tires are often re-used for things from bumper car barriers to weights to hold down tarps. Some facilities are permitted to recycle scrap tires through chipping, and processing into new products, or selling the material to licensed power plants for fuel. Some tires may also be retreaded for re-use. One group did "a study to evaluate the possibility of using scrap tires as a crash cushion system. The objective of this study was to evaluate the material properties of used tires and recycled tire-derived materials for use in low-cost, reusable crash cushions".^[46]

An interesting use, developed over 30 years back but not yet universally used, is to process scrap tires as raw material for roads. The process is removing the metal, granulating the rubber and then a chemical process where it is mixed with other usual materials for macadamised roads. The resulting roads have proved to have better waterproofing, more resilent resulting in a smoother ride and also longer tire life. Several countries (for example, South Korea) have regulations requiring its use, but most do not.

Americans generate about 285 million scrap tires per year.^[47] Many states have regulations as to the number of scrap tires that you may have on site, due to concerns with dumping, fire hazards, and mosquitoes. In the past, millions of tires have been discarded into open fields. This creates a breeding ground for mosquitoes, since the tires often hold water inside and remain warm enough for mosquito breeding. Mosquitoes create a nuisance and may increase the likelihood of spreading disease. It also creates a fire danger, since such a large tire pile is a lot of fuel. Some tire fires have burned for months, since water does not adequately penetrate or cool the burning tires. Tires have been known to liquefy, releasing hydrocarbons and other contaminants to the ground and even ground water, under extreme heat and temperatures from a fire. The black smoke from a tire fire causes air pollution and is a hazard to down wind properties.

The use of scrap tire chips for landscaping has become controversial, due to the leaching of metals and other contaminants from the tire pieces. Zinc is concentrated (up to 2% by weight) to levels high enough to be highly toxic to aquatic life and plants.^[48] Of particular concern is evidence that some of the compounds that leach from tires into water, contain hormone disruptors and cause liver lesions.^[49]

Asymmetric tire

An asymmetric tire is a term used to describe some specific stabilization methods used in cars.

Tire tread

An asymmetric tire may refer to a tire whose tread pattern does not form in line symmetry or point symmetry vis-à-vis its central line, thus having a distinct inside and outside edge. They may be mounted on either side of the vehicle. Since the tread pattern of many ordinary tires do not form symmetry in relation to design or pattern noise, the method of mounting tires is specially prescribed. This type of tires is used in many cases to promote tire performance, braking performance, and turning performance, since tread contact changes according to the change in alignment during travel.

Tires may also be directional, where the tread pattern favors operation in one direction. This usually takes the form of v-shaped grooves that help to disperse water from the center to the edge of the tread. Symmetric directional tires can be used on both sides, but once mounted on a rim cannot be moved to the other side, since the tread pattern will be in the wrong direction. This restricts tire rotation. Some directional tires are also asymmetric, in which case there will be specific left and right-handed versions.

Stabilizing belts

An asymmetric tire may refer to a passenger car radial tire in which asymmetric structure stabilizing belts are built. Generally the stabilizing belts give a self-aligning torque when a motor vehicle is running straight ahead as well as when it is cornering. However, the sidewalls of the radial tire are so flexible that there will be a delay in the lateral reaction between the tread of the tire and the rim of its wheel as the vehicle is being steered positively. The lateral force will be transmitted from the front wheel to the rear of the vehicle, which will tend to be steered off course. Whereas the asymmetric belts bring a gradual change in the lateral displacement of the tire tread corresponding to the rim while the cornering load grows. The progressive change will harden the sidewalls to produce an immediate response to steering, which results in safer driving.

See also

References

External links

• National Highway Traffic Safety Adm "Tire Safety" Brochure
• U.S. Government tire rating and maintenance site.

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