Assorted new automotive road tires, showing a variety of tread patterns.Tractor tires have substantial ribs and voids for traction in soft terrain.
Atire (North American English) ortyre (Commonwealth English) is a ring-shaped component that surrounds awheel's rim to transfer a vehicle's load from theaxle through the wheel to the ground and to providetraction on the surface over which the wheel travels. Most tires, such as those for automobiles and bicycles, arepneumatically inflated structures, providing a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint, called acontact patch, designed to match the vehicle's weight and the bearing on the surface that it rolls over by exerting a pressure that will avoid deforming the surface.
The materials of modernpneumatic tires aresynthetic rubber,[1]natural rubber, fabric, and wire, along withcarbon black and other chemical compounds. They consist of atread and a body. The tread providestraction while the body provides containment for a quantity ofcompressed air. Beforerubber was developed, tires were metal bands fitted around wooden wheels to hold the wheel together under load and to prevent wear and tear. Early rubber tires were solid (not pneumatic). Pneumatic tires are used on many vehicles, includingcars,bicycles,motorcycles,buses,trucks,heavy equipment, andaircraft. Metal tires are used onlocomotives andrailcars, and solid rubber (or other polymers) tires are also used in various non-automotive applications, such ascasters,carts,lawnmowers, andwheelbarrows.
Unmaintained tires can lead to severe hazards for vehicles and people, ranging fromflat tires making the vehicle inoperable toblowouts, where tires explode during operation and possibly damage vehicles and injure people. The manufacture of tires is often highly regulated for this reason. Because of the widespread use of tires for motor vehicles, tire waste is a substantial portion of global waste. There is a need fortire recycling through mechanical recycling and reuse, such as forcrumb rubber and othertire-derived aggregate, andpyrolysis for chemical reuse, such as fortire-derived fuel. If not recycled properly orburned, waste tires release toxic chemicals into the environment. Moreover, the regular use of tires producesmicro-plastic particles that contain these chemicals that both enter the environment and affect human health.[2]
The wordtire is a short form ofattire, from the idea that a wheel with a tire is a dressed wheel.[3][4]
Tyre is the oldest spelling,[5] and bothtyre andtire were used during the 15th and 16th centuries. During the 17th and 18th centuries,tire became more common in print. The spellingtyre did not reappear until the 1840s when the English began shrink-fitting railway car wheels with malleable iron. Nevertheless, many publishers continued usingtire.The Times newspaper in London was still usingtire as late as 1905.[6] The spellingtyre began to be commonly used in the 19th century for pneumatic tires in the UK. The1911 edition of theEncyclopædia Britannica states that"The spelling 'tyre' is not now accepted by the best English authorities, and is unrecognized in the US",[7] whileFowler'sModern English Usage of 1926 describes 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".[8] However, over the 20th century,tyre became established as the standard British spelling.[4]
The earliest tires were bands ofleather,[9] theniron (latersteel) placed on wooden wheels used on carts andwagons. A skilled worker, known as awheelwright, would cause the tire to expand by heating it in aforge fire, placing it over the wheel, and quenching it, causing the metal to contract back to its original size to fit tightly on the wheel.
The first patent for what appears to be a standard pneumatic tire appeared in 1847 and was lodged by Scottish inventorRobert William Thomson.[10] However, this idea never went into production. The first practical pneumatic tire was made in 1888 on May Street,Belfast, by Scots-bornJohn Boyd Dunlop, owner of one of Ireland's most prosperous veterinary practices. It was an effort to prevent the headaches of his 10-year-old son Johnnie while riding histricycle on rough pavements. His doctor, John, later Sir John Fagan, had prescribed cycling as an exercise for the boy and was a regular visitor. Fagan participated in designing the first pneumatic tires. CyclistWillie Hume demonstrated the supremacy of Dunlop's tires in 1889, winning the tire's first-ever races in Ireland and then England.[11][12] In Dunlop's tire patent specification dated 31 October 1888, his interest is only in its use in cycles and light vehicles. In September 1890, he was made aware of an earlier development, but the company kept the information to itself.[13] In 1892, Dunlop's patent was declared invalid because of the prior art by forgotten fellow Scot Robert William Thomson of London (patents London 1845, France 1846, USA 1847). However, Dunlop is credited with "realizing rubber could withstand the wear and tear of being a tire while retaining its resilience".[14] John Boyd Dunlop andHarvey du Cros worked through the ensuing considerable difficulties. They employed inventor Charles Kingston Welch and acquired other rights and patents, which allowed them some limited protection of theirPneumatic Tyre business's position. Pneumatic Tyre would become Dunlop Rubber andDunlop Tyres. The development of this technology hinged on myriad engineering advances, including thevulcanization of natural rubber using sulfur, as well as the development of the "clincher" rim for holding the tire in place laterally on the wheel rim.
Synthetic rubbers were invented in the laboratories ofBayer in the 1920s.[15] Rubber shortages in the United Kingdom during WWII prompted research on alternatives to rubber tires with suggestions including leather, compressed asbestos, rayon, felt, bristles, and paper.[16]
In 1946,Michelin developed theradial tire method of construction. Michelin had bought the bankruptCitroën automobile company in 1934 to utilize this new technology. Because of its superiority in handling and fuel economy,[17] use of this technology quickly spread throughout Europe and Asia.[18] In the US, the outdated bias-ply tire construction persisted until the Ford Motor Company adopted radial tires in the early 1970s,[19] following a 1968 article in an influential American magazine,Consumer Reports, highlighting the superiority of radial construction.[20][21] The US tire industry lost its market share to Japanese and European manufacturers,[22] which bought out US companies.[23]
Tires may be classified according to the type of vehicle they serve. They may be distinguished by the load they carry and by their application, e.g. to a motor vehicle, aircraft, or bicycle.
Studded winter tireA winter tire without studs, showing tread pattern designed to compact snow in the gaps.[24]High-performancerally tires
Light-duty tires for passenger vehicles carry loads in the range of 250 to 500 kilograms (550 to 1,100 lb) on the drive wheel. Light-to-medium duty trucks and vans carry loads in the range of 500 to 1,500 kilograms (1,100 to 3,300 lb) on the drive wheel.[25] They are differentiated byspeed rating for different vehicles, including (starting from the lowest speed to the highest): winter tires, light truck tires, entry-level car tires, sedans and vans, sport sedans, and high-performance cars.[26] Apart from road tires, there are special categories:
Snow tires are designed for use onsnow andice. They have atread design with larger gaps than those on summer tires, increasingtraction on snow and ice. Such tires that have passed a specific winter traction performance test are entitled to display a "Three-Peak Mountain Snow Flake" symbol on their sidewalls. Tires designed for winter conditions are optimized to drive at temperatures below 7 °C (45 °F). Some snow tires have metal or ceramic studs that protrude from the tire to increase traction on hard-packed snow or ice. Studs abrade dry pavement, causing dust and creating wear in the wheel path.[27] Regulations that require the use of snow tires or permit the use of studs vary by country in Asia and Europe, and by state or province in North America.
All-season tires are typically rated for mud and snow (M+S). These tires have tread gaps that are smaller than snow tires and larger than conventional tires. They are quieter than snow tires on clear roads, but less capable on snow or ice.[28]
All-terrain tires are designed to have adequate traction off-road, yet have benign handling and noise characteristics for highway driving.[29] Such tires are rated better on snow and rain than street tires and "good" on ice, rock, and sand.[30]
Mud-terrain tires have a deeper, more open tread for good grip in mud, than all-terrain tires, but perform less well on pavement.[31]
High-performance tires are rated for speeds up to 270 kilometres per hour (168 mph) and ultra-high-performance tires are rated for speeds up to 299 kilometres per hour (186 mph), but have harsher ride characteristics and durability.[32]
Electric vehicles have unique demands on tires due to the combination of weight (resulting in new load index), higher torque, and requirements for lower rolling resistance.[33]
Other types of light-duty automotive tires include run-flat tires and race car tires:
Run-flat tires eliminates the need for a spare tire because they can be traveled on at a reduced speed in the event of a puncture, using a stiff sidewall to prevent damage to the tire rim.[34] Vehicles without run-flat tires rely on a spare tire, which may be a compact tire, to replace a damaged tire.[34]
Race car tires come in three main categories,DOT (street-legal),slick, andrain. Race car tires are designed to maximize cornering and acceleration friction at the expense of longevity. Racing slicks have no tread to maximize contact with the pavement and rain tires have channels to eject water to avoidhydroplaning.[35]
Heavy-duty tires for large trucks and buses come in a variety of profiles and carry loads in the range of 1,800 to 2,500 kilograms (4,000 to 5,500 lb) on the drive wheel.[25] These are typically mounted in tandem on the drive axle.[34]
Truck tires come in a variety of profiles that include "low profile" with a section height that is 70 to 45% of the tread width, "wide-base" for heavy vehicles, and a "super-single" tire that has the same total contact pressure as a dual-mounted tire combination.[34]
Off-road tires are used on construction vehicles, agricultural and forestry equipment, and other applications that take place on soft terrain. The category also includes machinery that travels over hardened surfaces at industrial sites, ports, and airports.[36] Tires designed for soft terrain have a deep, wide tread to provide traction in loose dirt, mud, sand, or gravel.[37]
Aircraft tires are designed for landing on paved surfaces and rely on theirlanding gear to absorb the shock of landing. To conserve the weight and space required, they are typically small in proportion to the vehicle that they support. Most are radial-ply construction. They are designed for a peak load when the aircraft is stationary, although side loads upon landing are an important factor.[38] Although hydroplaning is a concern for aircraft tires, they typically have radial grooves and no lateral grooves or sipes.[39] Some light aircraft employ large-diameter, low-pressuretundra tires for landing on unprepared surfaces in wilderness areas.[40]
Bicycle tires may be designed for riding on roads or over unimproved terrain and may be mounted on vehicles with more than two wheels. There are three main types:clincher,wired andtubular.[41] Most bicycle tires areclincher and have a bead that presses against the wheel rim. An inner tube provides the air pressure and the contact pressure between the bead and wheel rim.[42]
Industrial tires support such vehicles as forklifts, tractors, excavators, road rollers, and bucket loaders. Those used on smooth surfaces have a smooth tread, whereas those used on soft surfaces typically have large tread features.[43] Some industrial tires are solid or filled with foam.[44]
Motorcycle tires provide traction, resisting wear, absorbing surface irregularities, and allow themotorcycle to turn viacountersteering. The two tires' contact with the ground affects safety, braking, fuel economy, noise, and rider comfort.[45][self-published source?]
A cross-section of a tire showing ply orientations
Tire construction spanspneumatic tires used on cars, trucks, and aircraft, but also includes non-automotive applications with slow-moving, light-duty, or railroad applications, which may have non-pneumatic tires.
Following the 1968Consumer Reports announcement of the superiority of the radial design,radial tires began an inexorable climb in market share, reaching 100% of the North American market in the 1980s.[20] Radial tire technology is now the standard design for essentially all automotive tires, but other methods have been used.[26]
Radial (or radial-ply) tire construction utilizes body ply cords extending straight across the tread from bead to bead—so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to one another—as well as stabilizer belts directly beneath the tread. The plies are generally made of nylon, polyester, or steel, and the belts of steel, fiberglass, orKevlar.[46][47] The tire’s footprint, wider than a bias tire’s, and flexible sidewalls provide a better grip in turns, and its circumferential belts stabilize it. The advantages of this construction over that of a bias tire are many, including longer tread life, better steering control, lowerrolling resistance, improved fuel economy, more uniform wear, higher heat resistance, fewer blowouts, and a steadier, more comfortable ride at speed. Disadvantages, besides a higher cost than that of bias tires, are a harder ride at low speeds and generally worse performance on rough terrain.[48][49][26] Radial tires are also seldom seen in diameters of greater than 42 inches, as such tires are difficult to make.[50]
Bias tire (bias-ply, 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 from the direction of travel.[51] Successive plies are laid at opposing angles, forming a crisscross pattern to which the tread is applied. Such a design is resistant to sidewall deformation and punctures (and to punctures’ expansion, or “torque splitting”) and therefore durable in severe use.[52] Since the tread and sidewalls share their casing plies, the tire body flexes as a whole, providing the main advantage of this construction, better traction and smoother motion on uneven surfaces, with a greater tendency to conform to rocky ground and throw off mud and clay, especially because the rubber is usually of a softer compound than that used on radial tires. However, this conformity increases a bias tire's rolling resistance, and its stiffness allows less control,traction, and comfort at higher speeds, whileshear between its overlapping plies causes friction that generates heat.[53][54][55][26] Still, bias tires benefit from simpler structure and so cost less than like-size radials, and they remain in use on heavy equipment and off-road vehicles, although the earthmoving market has shifted to radials.[26][56]
A belted bias tire starts with two or more bias plies to which stabilizer belts are bonded directly beneath the tread. This construction provides a smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. The design was introduced by Armstrong, while Goodyear made it popular with the "Polyglas" trademark tire featuring a polyester carcass with belts of fiberglass.[57] The "belted" tire starts two main plies of polyester, rayon, or nylon annealed as in conventional tires, and then placed on top are circumferential belts at different angles that improve performance compared to non-belted bias tires. The belts may be fiberglass or steel.[57]
Semi-pneumatic tires have a hollow center, but they are not pressurized. They are lightweight, low-cost, puncture-proof, and provide cushioning.[58] These tires often come as a complete assembly with the wheel and even integralball bearings. They are used onlawn mowers,wheelchairs, andwheelbarrows. They can also be rugged, typically used in industrial applications,[59] and are designed to not pull off theirrim under use.
Anairless tire is a non-pneumatic tire that is not supported by air pressure. They are most commonly used on small vehicles, such as golf carts, and on utility vehicles in situations where the risk of puncture is high, such as on construction equipment. 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 lawnmowers, 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 utilizing a hydraulic tire press.
The wheels of some railway engines and older types of rolling stock are fitted withrailway tires to prevent the need to replace the entirety of a wheel. The tire, usually made of steel, surrounds the wheel and is primarily held in place byinterference fit.
Aircraft tires may operate at pressures that exceed 1,400kilopascals (14 bar; 200 psi).[60] Some aircraft tires are inflated withnitrogen to "eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile gases from the tire inner liner producing a tire explosion".[61]
Pneumatic tires are manufactured in about 450 tire factories around the world. Tire production starts with bulk raw materials such as rubber, carbon black, and chemicals and produces numerous specialized components that are assembled and cured. Many kinds of rubber are used, the most common beingstyrene-butadienecopolymer.[62]
Forecasts for the global automotive tire market indicate continued growth through 2027. Estimates put the value of worldwide sales volume around $126 billion in 2022, it is expected to reach the value of over $176 billion by 2027.[63] Production of tires is also experiencing growth. In 2015, the US manufactured almost 170 million tires.[64] Over 2.5 billion tires are manufactured annually, making the tire industry a major consumer of natural rubber. It was estimated that for 2019 onwards, at least 3 billion tires would be sold globally every year.[65] However, other estimates put worldwide tire production of 2,268 million in 2021 and is predicted to reach 2,665 million tires by 2027.[66]
As of 2011, the top three tire manufacturing companies by revenue wereBridgestone (manufacturing 190 million tires),Michelin (184 million),Goodyear (181 million); they were followed byContinental, andPirelli.[67][68] TheLego group produced over 318 milliontoy tires in 2011 and was recognized byGuinness World Records as having the highest annual production of tires by any manufacturer.[69][70]
Components of a radial tireMountain bicycle tires with an open-lug pattern for grip in soft soilAbsence of grooves maximizes dry-pavement friction on a set of slickFormula One tires
A tire comprises several components: the tread, bead, sidewall, shoulder, and ply.
Thetread 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 thecontact 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.[71]
The tread pattern is characterized by a system of circumferential grooves, lateral sipes, and slots for road tires[26] or a system of lugs andvoids for tires designed for soft terrain or snow. 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. Grooves, sipes, and slots allow tires to evacuate water.
The design of treads and the interaction of specific tire types with the roadway surface affectsroadway noise, a source ofnoise pollution emanating from moving vehicles. These sound intensities increase with higher vehicle speeds.[72] Tires treads may incorporate a variety of distances between slots (pitch lengths) to minimize noise levels at discrete frequencies. Sipes are slits cut across the tire, usually perpendicular to the grooves, which allow the water from the grooves to escape sideways and mitigatehydroplaning.[26]
Different tread designs address a variety of driving conditions. As the ratio of tire tread area to groove area increases, so does tire friction on dry pavement, as seen onFormula One tires, some of which have no grooves. High-performance tires often have smaller void areas 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.[73] Mud and snow (M&S) tires employ larger and deeper slots to engage mud and snow.[26]Snow tires have still larger and deeper slots that compact snow and create shear strength within the compacted snow to improve braking and cornering performance.[74]
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, typically at a remaining tread depth of 1.6 millimetres (0.063 in).[75]
Thetire bead is the part of the tire that contacts therim on the wheel. This essential component is constructed with robust steel cables encased in durable, specially formulated rubber designed to resist stretching. The precision of the bead's fit is crucial, as it seals the tire against the wheel, maintaining air pressure integrity and preventing any loss of air. The bead's design ensures a secure, non-slip connection, preventing the tire from rotating independently from the wheel during vehicle motion. Additionally, the interplay between the bead's dimensions and the wheel's width significantly influences the vehicle's steering responsiveness and stability, as it helps to maintain the tire’s intended shape and contact with the road.
The sidewall is that part of the tire, orbicycle tire, that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for tensile strength and flexibility. The sidewall contains air pressure and transmits the torque applied by the drive axle to the tread to create traction but supports little of the weight of the vehicle, as is clear from the total collapse of the tire when punctured.
Sidewalls are molded with manufacturer-specific detail, government-mandated warning labels, and other consumer information.[76][77]
Sidewall may also have sometimes decorative ornamentation that includeswhitewall or red-line inserts as well astire lettering.[78]
The shoulder is that part of the tire at the edge of the tread as it makes the transition to the sidewall.[79]
Plies are layers of relatively inextensible cords embedded in the rubber[80] to hold its shape by preventing the rubber from stretching in response to the internal pressure. The orientations of the plies play a large role in the performance of the tire and are one of the main ways that tires are categorized.[81]
Blem (short for "blemished") is a term used for a tire that failed inspection during manufacturing - but only for superficial/cosmetic/aesthetic reasons. For example, a tire with white painted lettering which is smudged or incomplete might be classified as a "blem". Blem tires are fully functional and generally carry the same warranty as flawless tires - but are sold at a discount.[82]
The cords, which form the ply and bead and provide the tensile strength necessary to contain the inflation pressure, can be composed ofsteel, natural fibers such ascotton orsilk, or synthetic fibers such asnylon orkevlar. Good adhesion between the cords and the rubber is important. To achieve this the steel cords are coated in a thin layer of brass,[83] various additives will also be added to the rubber to improve binding, such asresorcinol/HMMM mixtures.
The elastomer, which forms thetread and encases the cords to protect them from abrasion and hold them in place, is a key component of pneumatic tire design. It can be composed of various composites of rubber material – the most common beingstyrene-butadiene copolymer – with other chemical compounds such assilica andcarbon black.
Optimizingrolling resistance in the elastomer material is a key challenge for reducing fuel consumption in the transportation sector. It is estimated that passenger vehicles consume approximately 5~15% of their fuel to overcome rolling resistance, while the estimate is understood to be higher for heavy trucks.[84] However, there is a trade-off between rolling resistance and wet traction and grip: while low rolling resistance can be achieved by reducing the viscoelastic properties of the rubber compound (lowtangent (δ)), it comes at the cost of wet traction and grip, which requireshysteresis and energy dissipation (high tangent (δ)). A low tangent (δ) value at 60 °C is used as an indicator of low rolling resistance, while a high tangent (δ) value at 0 °C is used as an indicator of high wet traction.[31] Designing an elastomer material that can achieve both high wet traction and low rolling resistance is key in achieving safety and fuel efficiency in the transportation sector.
The most common elastomer material used today is astyrene-butadiene copolymer. It combines the properties ofpolybutadiene, which is a highly rubbery polymer (Tg = -100 °C) having high hysteresis and thus offering good wet grip properties, with the properties ofpolystyrene, which is a glassy polymer (Tg = 100 °C) having low hysteresis and thus offering low rolling resistance in addition towear resistance. Therefore, the ratio of the two monomers in the styrene-butadiene copolymer is considered key in determining theglass transition temperature of the material, which is correlated to its grip and resistance properties.[85]
Non-exhaust emissions of particulate matter, generated by the wearing down of brakes, clutches, tires, and road surfaces, as well as by the suspension of road dust, constitute a little-known but rising share of emissions from road traffic and significantly harm public health.[86]
Associated components of tires include the wheel on which it is mounted, the valve stem through which air is introduced, and, for some tires, an inner tube that provides the airtight means for maintaining tire pressure.
Wheel: Pneumatic tires are mounted ontowheels that most often have integral rims on their outer edges to hold the tire. Automotive wheels are typically made from pressed and welded steel, or a composite of lightweight metalalloys, such as aluminum or magnesium. There are two aspects to how pneumatic tires support the rim of the wheel on which they are mounted.[87] First, the tension in thecords pull on thebead uniformly around the wheel, except where it is reduced above the contact patch.[88] Second, the bead transfers that net force to the rim.[89][88] Tires are mounted on the wheel by forcing its beads into the channel formed by the wheel's inner and outer rims.[90][91]
Valve stem: Pneumatic tires receive their air through avalve stem—a tube made of metal or rubber, with acheck valve, typically aSchrader valve on automobiles and most bicycle tires, or aPresta valve on high-performance bicycles. They mount directly to the rim, in the case of tubeless tires, or are an integral part of the inner tube. Most modern passenger vehicles are now required to have atire pressure monitoring system which usually consists of a valve stem attached to an electronic module.[34]
Inner tube: Mostbicycle tires, manymotorcycle tires, and many tires for large vehicles such as buses, heavy trucks, and tractors are designed for use withinner tubes. Inner tubes aretorus-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 can be reused for other purposes, such as swimming and rafting (seeswim ring),tubing (recreation),sledding, andskitching. Purpose-built inflatable tori are also manufactured for these uses, offering a choice of colors, fabric covering, handles, decks, and other accessories, and eliminating the protruding valve stem.
The interactions of a tire with the pavement are complex. A commonly used (empirical) model of tire properties isPacejka's "Magic Formula".[92] Some are explained below, alphabetically, by section.
Balance: Wheel-tire combinations require an even distribution of mass around their circumferences to maintaintire balance, while turning at speed. 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. An alternative method to tire balancing is the use of internal tire balancing agents. These agents take advantage of centrifugal force and inertia to counteract the tire imbalance.[93] 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.[94]
Centrifugal growth: A tire rotating at higher speeds tends to develop a larger diameter, due tocentrifugal forces that force the tread rubber away from the axis of rotation. This may causespeedometer error. As the tirediameter 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.[26]
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 resultantforce ofside-slip occurs behind the geometric center of thecontact patch.[95]
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).[26]
Relaxation length:Relaxation length is the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value.[26]
Spring rate: Vertical stiffness, orspring rate, is the ratio of vertical force to vertical deflection of the tire, and it contributes to the overall suspension performance of the vehicle. In general, the spring rate increases with inflation pressure.[96]
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.[26]
Camber thrust:Camber thrust and camber force are the force generated perpendicular to the direction of travel of a rolling tire due to itscamber angle and finite contact patch.[26]
Circle of forces: Thecircle 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.[97]
Contact patch: Thecontact 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.[26]
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.[26]
Dry traction: Dry traction is the 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.[26]
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 deformed during this cycle. As the rubber deforms and recovers, it imparts cyclical forces into the vehicle. These variations are collectively referred to astire uniformity. Tire uniformity is characterized byradial force variation (RFV),lateral force variation (LFV), andtangential force variation. Radial and lateral force variation is measured on aforce 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.[26]
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, the 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 to improvefuel economy in cars and especially trucks, where rolling resistance accounts for a high proportion of fuel consumption. Pneumatic tires also have 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.[26]
Self aligning torque:Self-aligning torque, also known as the aligning torque, SAT or Mz, is thetorque that a tire creates as it rolls along that tends to steer it, i.e. rotate it around its vertical axis.[26]
Wet traction: Wet traction is the tire'straction, or grip, under wet conditions. Wet traction is improved by the tread design's ability to channel water out of the tire footprint and reducehydroplaning. 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.[98]
Load sensitivity:Load sensitivity is the behavior of tires under load. Conventional pneumatic tires do not behave asclassical 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.[26]
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.[99] Work load is measured inTon Kilometer Per Hour (TKPH). The measurement's appellation and units are the same. The recent shortage and increasing cost of tires forheavy 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.[100][101] 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 isTon Mile Per Hour (TMPH).
Tire wear is a major source ofrubber pollution. A concern hereby is that vehicle tire wear pollution is unregulated, unlike exhaust emissions.[102]
Tire showing uneven tread wear to the point of exposing the casing
Tread wear
This occurs through normal contact with roads or terrain; there are several types of abnormal tread wear. Poorwheel alignment can cause excessive wear of the innermost or outermost ribs. Gravel roads, rocky terrain, and other rough terrain cause 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. 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.[26]
Wear bar and tread wear indicator on the snow tire tread
Tread wear indicators (T.W.I.)
Raised bars in the tread channels, which indicate that the tread is becoming worn and therefore unsafe. Indicators have been required on all new tires since 1968 in the US.[103] In many countries the Highway Code forbids driving on public roads when the contact surface is flush with any of these bars - this is often defined when the groove depth is approximately 1.5 or 1.6 mm (2/32 inch). TWI can also be used to refer to small arrows or icons on the tire sidewall, indicating the location of the raised wear bars.
Damage by aging
Tire aging or "thermo-oxidative degradation" can be caused by time, ambient and operating temperatures, partial pressure of O2 in a tire, flex fatigue, or construction and compounding characteristics. For example, prolonged UV exposure leads to rubber's chemicals warping, potentially causing dry rot. Various storage methods may slow the aging process, but will not eliminate tire degradation.[104]
Automotive tires have a variety of identifying markings molded onto the sidewall as atire code. They denote size, rating, and other information pertinent to that individual tire.
TheNational Highway and Traffic Safety Administration (NHTSA) is a U.S. government body within theDepartment of Transportation (DOT) tasked with regulating automotive safety in the United States.[105] NHTSA established the Uniform Tire Quality Grading System (UTQG), is a system for comparing the performance of tires according to the Code of Federal Regulations 49 CFR 575.104; it requires labeling of tires for tread wear, traction, and temperature. The DOT Code is analphanumeric character sequence molded into the sidewall of the tire and allows the identification of the tire and its age. The code is mandated by theU.S. Department of Transportation[105] but is used worldwide.[106] The DOT Code is also useful in identifying tires subject toproduct recall[107] or at end of life due to age. TheTire and Rim Association (T&RA) is a voluntary U.S. standards organization that promotes the interchangeability of tires, rims, and allied parts. Of particular interest, they publish key tire dimensions, rim contour dimensions, tire valve dimension standards, and load/inflation standards.
TheEuropean Tyre and Rim Technical Organisation (ETRTO) is the European standards organization "to establish engineering dimensions, load/pressure characteristics and operating guidelines".[109] 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 (lowercase) "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.[110]
TheBritish Rubber Manufacturers Association (BRMA) recommended practice, issued June 2001, states, "BRMA members strongly recommend that unused tires should not be put into service if they are over six years old and that all tires should be replaced ten years from the date of their manufacture."[111]
The Japanese Automobile Tire Manufacturers Association (JATMA) is the Japanese standards organization for tires, rims, and valves.[112] It performs similar functions as the T&RA and ETRTO.
The China Compulsory Certification (CCC) is a mandatory certification system concerning product safety in China that went into effect in August 2002. 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).[113]
To maintain tire health, several actions are appropriate, tire rotation, wheel alignment, and, sometimes, retreading the tire.
Rotation: Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn.Front-wheel drive vehicles tend to wear the front tires at a greater rate compared to the rear tires. Tire rotation is moving the tires to different car positions, such as front-to-rear, in order to even out the wear, with the objective of extending the life of the tire.[114]
Alignment:Wheel alignment helps prevent wear due to rotation in a direction other than the path of the vehicle. 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 substantial if left uncorrected. Wheel alignment is the procedure for checking and correcting this condition through adjustment ofcamber,caster, andtoe angles. The adjustment of the angles should be done as per the OEM specifications.[115]
Rolling resistance as a function of tire inflation
Inflation is key to proper wear and rolling resistance of pneumatic tires. Many vehicles have monitoring systems to assure proper inflation. Most passenger cars are advised to maintain a tire pressure within the range of 220 to 240kilopascals (32 to 35 psi) when the tires are not warmed by driving.[116][117]
Specification— Vehicle manufacturers provide tire specifications, including a recommendedcold inflation pressure, to ensure safe operation within the designated load rating and vehicle loading capacity. While many tires feature a maximum pressure rating stamped on them, passenger vehicles and light trucks typically include inflation guidance on a decal located just inside the driver's door and in the vehicle owner's handbook.[118]
Ground contact: The tire contact patch is readily changed by both over- and underinflation. Overinflation may increase the wear on the center contact patch, and underinflation will cause a concave tread, resulting in less center contact, though the overall contact patch will still be larger.[119] Most modern tires will wear evenly at high tire pressures, but will degrade prematurely if underinflated. Increased tire pressure may decrease rolling resistance, and may also result in shorter stopping distances[120] If tire pressure is too low, the tire contact patch is greatly increased. This increases rolling resistance, tire flexing, and friction between the road and the tire. Under-inflation can lead to tire overheating, premature tread wear, and tread separation in severe cases.[121]
Monitoring: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.
Tire bubbleTire showing weather-cracking over long-term exposure to the weatherA flat tire on a passenger car
Tire hazards may occur from failure of the tire, itself, or from loss of traction on the surface over which it is rolling. Structural failures of a tire can result inflat tires or more dangerousblowouts. Some of these failures can be caused by manufacture error and may lead to recalls, such as the widespread Firestone tire failures on Ford vehicles that lead to theFirestone and Ford tire controversy in the 1990s.
Tires may fail for any of a variety of reasons, including:[122]
Belt separation which may be belt-to-belt, tread and belt, or separation of the edge of the belt. Belt-to-belt separation may occur having the tire deflect too much, from high pavement temperatures, road hazard impacts, or other causes that have to do with maintenance and storage.
Non-belt separations include those at the tire tread, in the bead area, in the lower sidewall, between reinforcing plies, and of the reinforcing steel or fabric materials.
Other types of failure include run-flat damage, chemical degradation, cracking, indentations and bulges.
Melting rubber: As tire rubber compounds heat, owing to the friction of stopping, cornering, or accelerating, they may begin to melt, lubricate the tire-road contact area, and become deposited on the pavement. This effect is stronger with increased ambient temperature.[26]
Hydroplaning: Motor vehicles or aircraft tires passing over a wet pavement may lose contact with sufficient speed or water depth for a given tread design. In this case, the tire contact area is riding on a film of water and loses the friction needed for braking or cornering and begins tohydroplane (oraquaplane). Hydroplaning may occur asdynamic hydroplaning where standing water is present with a depth of at least 3 millimetres (0.12 in) above the texture of the pavement and speed is sustained above a threshold level. It may also occur asviscous hydroplaning whereby tire rubber melts for a brief interval and causes slippage. This may leave deposits of rubber on arunway as airplanes land.[123] Dynamic hydroplaning causes decreased friction and contact with increased tire speed.[124]
Snow: The degree to which a tire can maintain traction in snow depends on its ability to compact snow, which material then develops strength against slippage along a shear plane parallel to the contact area of the tire on the ground.[125] At the same time, the bottom of the tire treads compress the snow on which they are bearing, also creating friction. The process of compacting snow within the treads requires it to be expelled in time for the tread to compact snow anew on the next rotation. The compaction/contact process works both in the direction of travel for propulsion and braking, but also laterally for cornering.[74]
Ice: Ice is typically close to its melting point when a tire travels over it. This, combined with a smooth texture, promotes a low coefficient of friction and reduced traction during braking, cornering or acceleration.[26]
Soft ground: Soil can become lubricated with water, which reduces its ability to maintain shear strength when a tire tries to apply force in acceleration, braking, or cornering. Dry sand also has low shear strength, owing to poor cohesiveness among sand particles.[126]
As tires are used for vehicle operations, the natural wear of the tire leaves microfine particles equivalent toPM0.1,PM2.5, andPM10 as tire residue.[2] This residue accumulates near roadways and vehicle use areas, but also will travel into the environment throughsurface runoff.[2] Both humans and animals are exposed to these chemicals at the site of accumulation (i.e. walking on the road surface) and through the accumulation in natural environments and foodchains.[2] A 2023 literature review from Imperial College London, warned of both the toxic chemicals and microplastics produced from tire wear as having potential widespread serious environmental and health consequences.[2]
Moreover, burning of tires releases these chemicals as air pollutants as well as leaving toxic residues, that can have significant effects on local communities and first responders.[127]
Tires recycled into water tanks on the roof inCherchen, Xinjiang
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. Tires are not desired atlandfills, due to their large volumes and 75% void space, which quickly consumes valuable space. Rubber tires are likely to contain some traces ofheavy metals or other seriouspollutants, but these are tightly bonded within the actual rubber compound so they are unlikely to be hazardous unless the tire structure is seriously damaged by fire or strong chemicals.[128] Some facilities are permitted to recycle scrap tires by chipping and processing them into new products or selling the material to licensed power plants for fuel. Some tires may also be retreaded for re-use.
Americans generate about 285 million scrap tires per year.[129] Many states have regulations as to the number of scrap tires that can be held 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. Sometire fires have burned for months, since water does not adequately penetrate or cool theburning tires. Tires have been known to liquefy, releasing hydrocarbons and other contaminants to the ground and even groundwater, under extreme heat and temperatures from a fire. The black smoke from a tire fire causes air pollution and is a hazard to downwind 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.[130] Of particular concern is evidence that some of the compounds that leach from tires into the water contain hormone disruptors and cause liver lesions.[131]
Tires are a major source ofmicroplastic pollution, found in a 2020 study to contribute 78% of the total mass of microplastics found in the ocean.[132][133] The commonly-used compound6PPD-quinone, found entering stormwater runoff via tire-wear particles, has been identified as toxic to coho salmon, brook trout, and rainbow trout.[134]
Tires that are fully worn can beretreaded, re-manufactured to replace the worn tread.[135] This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread.[136] There are two main processes used for retreading tires, called mold-cure and pre-cure methods. Both processes start with the inspection of the tire, followed by non-destructive inspection method such asshearography[137] to locate non-visible damage and embeddeddebris and nails. Some casings are repaired and some are discarded. Tires can be retreaded multiple times if the casing is in usable condition. Tires used for short delivery vehicles are retreaded more than long haul tires over the life of the tire body. Casings fit for retreading have the old tread buffed away to prepare for retreading.[138]
During the retreading process, retread technicians must ensure the casing is in the best condition possible to minimize the possibility of a casing failure. Casings with problems such as capped tread, tread separation, irreparable cuts, corroded belts or sidewall damage, or any run-flat or skidded tires, will be rejected. 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.[138]
Tires can be recycled into, among other things, the hot meltasphalt, typically ascrumb rubber modifier—recycled asphalt pavement (CRM—RAP),[139][140] and as an aggregate inportland cementconcrete.[141] Shredded tires can createrubber mulch on playgrounds to diminish fall injuries.[142] There are some "green" buildings that are being made both private and public buildings that are made from old tires.[143]
Thetire pyrolysis method for recycling used tires is a technique that heats whole or shredded tires in a reactor vessel containing anoxygen-free atmosphere and a heat source. In the reactor, therubber is softened after which the rubber polymers continuously break down into smaller molecules.
Other downstream uses have been developed for worn-out tires, including:
Building elements: Tires filled with earth have been used as garden containers[144] house foundations,[145] bullet-proof walls[146] and to prevent soil erosion in flood plains.[147]Tire walls are a common feature ofmotor racing circuits for safety.
Recreational equipment: Used tires are employed as exercise equipment for athletic programs such asAmerican football.[148] One classic conditioning drill that hones players' speed and agility is the "Tire Run" where tires are laid out side by side, with each tire on the left a few inches ahead of the tire on the right in a zigzag pattern. Athletes then run through the tire pattern by stepping in the center of each tire. The drill forces athletes to lift their feet above the ground higher than normal to avoid tripping on the tires.[149] Old tires are sometimes converted into aswing for play.[150]
Burning tires as protest:Protestors, worldwide, have burned tires to create black smoke.[151][152]
Necklacing is the use of tires to kill people, typically bylynch mobs. A tire is soaked in gasoline, placed around the victim's neck, and set on fire.
^Chisholm, Hugh, ed. (1911)."Tire" .Encyclopædia Britannica. Vol. 26 (11th ed.). Cambridge University Press. pp. 1006–1009, see page 1007....The spelling " tyre " is not now accepted by the best English authorities, and is unrecognized in America...
^abcdefghijklmnopqrstuvwGent, Alan N.; Walter, Joseph D. (2006).The Pneumatic Tire(PDF). DOT HS 810 561. Washington, DC: National Highway Transportation Safety Administration. Archived fromthe original(PDF) on 9 March 2021. Retrieved3 May 2019.
^ab"Dynamic Mechanical Properties Of Passenger And Light Truck Tire Treads". Report No.DOTHS811 270. National Highway Traffic Safety Administration, U.S. Department of Transportation.2010.
^McKenny, Earl F. (May 1964).Aerospace safety. Washington, DC: United States Dept of the Air Force. pp. 5–7.
^Richfield, Paul J. (September 2005).Tundra Tire Nation. New York: Flying Magazine. pp. 88–92.
^Sharp, Archibald, Bicycles & Tricycles: An Elementary Treatise on Their Design and Construction, Longmans Green, London and New York, 1896, pages 494-502; reprinted by MIT Press, 1977,ISBN0-262-69066-7
^Rinard, Damon (2000)."Tire Bead Test".sheldonbrown.com. Retrieved10 March 2013.Conclusion: Clincher tires stay on the rim primarily by the clinch of the hooked sidewall that retains the tire bead, not the circumferential tension in the bead.
^Vanooij, William J.; Harakuni, Prasan B.; Buytaert, Guy (1 July 2009). "Adhesion of Steel Tire Cord to Rubber".Rubber Chemistry and Technology.82 (3):315–339.doi:10.5254/1.3548251.
^Hao, P. T., Ismail, H., & Hashim, A. S. (2001). Study of two types of styrene butadiene rubber in tire tread compounds.Polymer Testing,20(5), 539-544.
^Clark, Samuel K.; Gough, V.E. (1981).Mechanics of Pneumatic Tires. U.S. Department of Transportation. p. 245.Consider two mechanisms of force transmission acting in parallel.
^abClark, Samuel K.; Gough, V.E. (1981).Mechanics of Pneumatic Tires. U.S. Department of Transportation. p. 246.The only possible way in which the reaction can develop at the rim is by the changes in magnitude and direction of the membrane stresses at their points of attachment to the rim, in the region of the membrane near the point where the plate is pressed against it.
^Clark, Samuel K.; Gough, V.E. (1981).Mechanics of Pneumatic Tires. U.S. Department of Transportation. p. 246.This force pulls the bead coil against the base of the wheel rim above the contact area, thus transmitting the upward force to the wheel.
^Clark, Samuel Kelly (1981).Mechanics of pneumatic tires(PDF). U.S. Dept. of Transportation, National Highway Traffic Safety Administration, Washington, D.C.
^"Tire".The Rubber Age.100 (1). Palmerton Publishing: 102. 1968. Retrieved7 August 2019.One requirement provides that ... all new tires shall be equipped with a tread-wear indicator that will show at a glance when the tread depth has been worn to 1/16 of an inch.
^Liu, H., Mead, J., Stacer, R. Chelsea Center For Recycling And Economic Development. (1998). Environmental Impacts Of Recycling Rubber In Light Fill Applications: Summary & Evaluation Of Existing Literature University of Massachusetts
^"Tire-Derived Fuel". U.S. Environmental Protection Agency. Retrieved29 December 2011.
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