tire - wikipedia, the free encyclopedia

Stacked and standing car tires

TireFrom Wikipedia, the free encyclopedia

A tire (or tyre) is a ring-shaped covering that fits around a wheel's rim to protect it and enable bettervehicle performance. Most tires, such as those for automobiles and bicycles, provide tractionbetween the vehicle and the road while providing a flexible cushion that absorbs shock.

The materials of modern pneumatic tires are synthetic rubber, natural rubber, fabric and wire, alongwith carbon black and other chemical compounds. They consist of a tread and a body. The treadprovides traction while the body provides containment for a quantity of compressed air. Beforerubber was developed, the first versions of tires were simply bands of metal that fitted aroundwooden wheels to prevent wear and tear. Early rubber tires were solid (not pneumatic). Today, themajority of tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cordsand wires encased in rubber and generally filled with compressed air to form an inflatable cushion.Pneumatic tires are used on many types of vehicles, including cars, bicycles, motorcycles, trucks,earthmovers, and aircraft. Metal tires are still used on locomotives and railcars, and solid rubber (orother polymer) tires are still used in various non-automotive applications, such as some casters,carts, lawnmowers, and wheelbarrows.

Contents1 Etymology and spelling2 History3 Manufacturing4 Components5 Associated components6 Construction types7 Specifications8 Performance characteristics9 Markings10 Vehicle applications11 Sound and vibration characteristics12 Regulatory bodies13 Safety14 Asymmetric tire15 Other uses16 See also17 References18 External links

Etymology and spellingHistorically, the proper spelling is "tire" and is of French origin, coming from the word tirer, to pull. The reason for this naming is thatoriginally "tire" referred to iron hoops or thick wires bound to carriage wheels. In French blacksmithing the word for a drawn iron rod is atirer, or pull. The same word was often used for any metal drawing or rolling process. In an article in the London Magazine/Intelligencer of1853 "The Utility of Broad Wheels," it explains that the common practice was to bend two rods, called "tires," into hoops and bind them tothe wheel, but it is preferable to use an iron band, called a "broad wheel" rather than the rods, because as the rods wear they bite into thewheel. Another early mention of a tire in English is in The Scots Magazine, Volume 15 By James Boswell (1753).

The spelling tyre does not appear until the 1840s when the English began shrink fitting railway car wheels with malleable iron.Nevertheless, traditional publishers continued using tire. The Times newspaper in Britain was still using tire as late as 1905.[1] The spellingtyre, however, began to be commonly used in the 19th century for pneumatic tires in the UK. The 1911 edition of the EncyclopdiaBritannica states that "[t]he spelling 'tyre' is not now accepted by the best English authorities, and is unrecognized in the US",[2] whileFowler's Modern English Usage of 1926 says that "there is nothing to be said for 'tyre', which is etymologically wrong, as well as needlesslydivergent from our own [sc. British] older & the present American usage".[3] However, over the course of the 20th century tyre becameestablished as the standard British spelling.

Tire - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Tire

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Styrene-butadiene copolymer (chemical structurepictured) is the most popular material used in theproduction of rubber tires.[5]

2 bicycle tires with different tread patterns

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

The first practical pneumatic tire was made by John Boyd Dunlop while working as a veterinarian in May Street, Belfast, Ireland in 1887for his son's bicycle, in an effort to prevent the headaches his son had while riding on rough roads (Dunlop's patent was later declaredinvalid because of prior art by fellow Scot Robert William Thomson). Dunlop is credited with "realizing rubber could withstand the wearand tear of being a tire while retaining its resilience".[4] The development of this technology hinges on myriad engineering advances. Interms of materials, the vulcanization of natural rubber is credited to Charles Goodyear and Robert William Thomson. Synthetic rubberswere invented in the laboratories of Bayer in the 1920s.[5] Today, over 1 billion tires are produced annually in over 400 tire factories, seeList of Tire Companies.

ManufacturingMain article: Tire manufacturing

Pneumatic tires are manufactured in about 450 tire factories around the world. Over one billion tires are manufactured annually, making thetire industry a major consumer of natural rubber. It is estimated that by 2015, 1.72 billion tires are expected to be sold globally.[6] Tireproduction starts with bulk raw materials such as rubber, carbon black, and chemicals and produces numerous specialized components thatare assembled and cured. Many kinds of rubber are used, the most common being styrene-butadiene copolymer. This article describes thecomponents assembled to make a tire, the various materials used, the manufacturing processes and machinery, and the overall businessmodel.

In 2004, $80 billion of tires were sold worldwide,[7] in 2010 it was $140 billion.[8]

The top five tire manufacturing companies by revenue are Bridgestone, Michelin,Goodyear, Continental, and Pirelli.[9]

ComponentsA tire carcass is composed of several parts.

Tread

Main article: Tread

The tread is the part of the tire that comes in contact with the road surface. The portion that is incontact 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 doesnot wear away too quickly. The tread pattern is characterized by the geometrical shape of thegrooves, lugs, voids and sipes. Grooves run circumferentially around the tire, and are needed tochannel 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 patternsfeature non-symmetrical (or non-uniform) lug sizes circumferentially to minimize noise levelsat discrete frequencies. Sipes are valleys cut across the tire, usually perpendicular to thegrooves, which allow the water from the grooves to escape to the sides in an effort to preventhydroplaning.

Treads are often designed to meet specific product marketing positions. High performance tireshave small void ratios to provide more rubber in contact with the road for higher traction, but may be compounded with softer rubber thatprovides 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 beingused 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


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Uneven sidewall wear, down to fabricplies, due to significant under-inflation

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.[citation needed] These forces are described as ForceVariation.[citation needed]

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 areashave 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 arecircumferential in most truck tires. Many high performance passenger tires feature rain grooves that are angled from the center toward thesides of the tire.[citation needed] Some tire manufacturers claim that their tread pattern is designed to actively pump water out from under thetire by the action of the tread flexing.[citation needed] This results in a smoother ride in different types of weather.[citation needed]

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. Thisreduces shear stress in the lug and reduces heat build up. Testing of identical siped and unsiped tires showed measurable improvements insnow traction and ice braking performance, however diminishing and extending braking distances on wet and dry pavement by a few feeton siped tires. Off-road tire enthusiasts have been siping tires for years for greater traction, as many manufacturers now offer already sipedoff-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 ofservice. Most wear bars indicate a remaining tread depth of 1.6 millimetres (0.063 in) and are deemed "worn out" at that point.[10]

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 highstrength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air withoutleakage. The bead fit is tight to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship tothe 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 largelyrubber but reinforced with fabric or steel cords that provide for tensile strength and flexibility. Thesidewall contains air pressure and transmits the torque applied by the drive axle to the tread to createtraction but supports little of the weight of the vehicle, as is clear from the total collapse of the tirewhen punctured. Sidewalls are molded with manufacturer-specific detail, government mandatedwarning labels, and other consumer information, and sometimes decorative ornamentation, likewhitewalls.

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[11] to hold its shape by preventing the rubber from stretching inresponse to the internal pressure. The orientations of the plies play a large role in the performance of the tire and is one of the main waysthat tires are categorized.

Associated components


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Schrader valve stem with its capremoved

A cross-section of a tire showing plyorientations

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

Wheel

Main article: Wheel

Tires are mounted onto wheels that most often have integral rims on their outer edges to hold the tire. Automotive wheels are typically madefrom pressed and welded steel, or a composite of lightweight metal alloys, such as aluminum or magnesium. These alloy wheels may beeither cast or forged. The mounted tire and wheel assembly is then bolted to the vehicle's hub. A decorative hubcap and trim ring may beplaced over the wheel.

Rim

Main article: Rim (wheel)

The beads of the tire are held on the rim, or the "outer edge" of a wheel.[12] These outer edges are shaped to obtain a proper shape on eachside, having a radially cylindrical inclined inner wall on which the tire can be mounted. The wheel's rim must be of the proper design andtype to hold the bead of the appropriately sized tire.[13] Tires are mounted on the wheel by forcing its beads into the channel formed by thewheel's inner and outer rims.[14]

Inner tube

Most bicycle tires, many motorcycle tires, and many tires for large vehicles such as buses, heavy trucks, and tractors are designed for usewith inner tubes. Inner tubes are torus-shaped balloons made from an impermeable material, such as soft, elastic synthetic rubber, to preventair 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

Main article: Valve stem

The valve stem is a tube made of metal or rubber, through which the tire is inflated, with a checkvalve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve onhigh-performance bicycles. Valve stems usually protrude through the wheel for easy access. Theymount directly to the rim, in the case of tubeless tires, or are an integral part of the inner tube. Therubber in valve stems eventually degrades, and, in the case of tubeless tires, replacement of the valvestem 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 anglesforming a crisscross pattern to which the tread is applied. The design allows the entire tire body toflex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. Thiscushioning characteristic also causes the major disadvantages of a bias tire: increased rollingresistance 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 directlybeneath the tread. This construction provides smoother ride that is similar to the bias tire, whilelessening rolling resistance because the belts increase tread stiffness. The plies and belts are at different angles, which improvesperformance compared to non-belted bias tires. The belts may be cord or steel.

Radial


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Airless tire

Main article: Radial tire

Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximatelyright angles to the centerline of the tread, and parallel to each other, as well as stabilizer belts directly beneath the tread. The belts may becord 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.[15]

Solid

Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plasticcompounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types oflight 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 providecushioning.[16] These tires often come as a complete assembly with the wheel and even integral ball bearings. They are used on lawnmowers, wheelchairs, and wheelbarrows. They can also be rugged, typically used in industrial applications,[17] and are designed to not pulloff 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 andwheel), which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but theinterior has special compressible polyurethane springs to contribute to a comfortable ride. Besides the impossibility of going flat, the tiresare intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered bylow profile tires. They have not yet been delivered for broad market use.

Airless

Main article: Airless tire

Specifications

Tire pressure monitoring system

Main article: Tire pressure monitoring system

Tire pressure monitoring systems (TPMS) are electronic systems that monitor the tire pressures onindividual wheels on a vehicle, and alert the driver when the pressure goes below a warning limit. Thereare several types of designs to monitor tire pressure. Some actually measure the air pressure, and some make indirect measurements, such asgauging 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 specifiedload rating and vehicle loading. Most tires are stamped with a maximum pressure rating. For passenger vehicles and light trucks, the tiresshould be inflated to what the vehicle manufacturer recommends, which is usually located on a decal just inside the driver's door or in thevehicle owners handbook. Tires should not generally be inflated to the pressure on the sidewall; this is the maximum pressure, rather thanthe recommended pressure.[18]

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

Tires are not completely impermeable to air, and so lose pressure over time naturally. Some drivers inflate tires with nitrogen, instead ofsimple air, which is already 78% nitrogen, in an attempt to keep the tires at the proper inflation pressure longer,[19] though the effectivenessof this is debatable.[20][21][22]

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 tirepressures, but will degrade prematurely due to low (or even standard) pressures. An increased tire pressure has many benefits, including


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decreased rolling resistance. It has been found, that an increased tire pressure almost exclusively results in shorter stopping distances, exceptin some circumstances that may be attributed to the low sample size.[23] If tire pressure is too low, the tire contact patch is changed morethan if it were over-inflated. This increases rolling resistance, tire flexing, and friction between the road and tire. Under-inflation can lead totire overheating, premature tread wear, and tread separation in severe cases.[24]

High Pressure

High performance and dynamic drivers often increase the tire pressure to near the maximum pressure as printed on the sidewall. This isdone to sacrifice comfort for performance and safety. A tire at higher pressure is more inclined to keep its shape during any encounter, andwill 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 aresult the traditional wear on the center of the tire due to reasonably high pressures is only known to very old or poorly designed tires.

It may be, that very high tire pressures have only two downsides: The sacrifice in comfort; and the increased chance of obtaining a puncturewhen driving over sharp objects, such as on a newly scraped gravel road. Many individuals have maintained their tire pressures at themaximum side wall printed value (inflated when cold) for the entire lifetime of the tire, with perfect wear until the end. This may be ofnegative economic value to the rubber and tire companies, as high tire pressures decrease wear, and minimize side wall blowouts.[citation needed]

Low Pressure

It is dangerous to allow tire pressure to drop below the specification recommended on the vehicle placard. Low pressure increases theamount of tire wall movement resulting from cornering forces. Should a low-pressure tire be forced to perform an evasive maneuver, thetire wall will be more pliable than it would have been at normal pressure and thus it will "roll" under the wheel. This increases the entire rollmovement 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 offailing in the emergency maneuver is thus increased.

When driving on sand or in deep snow, tire pressure is sometimes lowered to reduce the chance of bogging down.

Furthermore, the tire will absorb more of the irregular forces of normal driving. With this constant bending of the side wall as it absorbs thecontours of the road, it heats up the tire wall to possibly dangerous temperatures. Additionally, this flexing degrades the steel wirereinforcement; this often leads to side wall blow-outs.

Low pressure tires can be subject to pinching. If the vehicle drives into a pot-hole, the side wall can temporarily collapse, thereby pinchingthe tire between the steel wheel and road. The can result in a tire laceration and blow-out, as well as a damaged wheel.

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 inabilityof the tire to perform appropriately during cornering forces, leading to aberrant and shearing forces on the feathering area. This is due to thetire moving sideways underneath the wheel as the tire pressures are insufficient to transmit the forces to the wheel and suspension.

Load rating

Tires are specified by the manufacturer with a maximum load rating. Loads exceeding the rating can result in unsafe conditions that canlead 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 99to 186 miles per hour (159 to 299 km/h). For a table of speed ratings, see tire code.

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 somefor stop-start multi-drop type work. Tires designed to run 500 miles (800 km) or more per day carrying heavy loads require specialspecifications.

Treadwear rating

Main article: Treadwear rating


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The treadwear rating or treadwear grade is how long the tire manufacturers expect the tire to last. A Course Monitoring Tire (the standardtire 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 areindicating 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 allmanufacturer-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 samerating. The testing is non-regulated and can vary greatly. Treadwear ratings are only useful for comparing Brand A's entire lineup againstitself. Tread wear, also known as tire wear, is caused by friction between the tire and the road surface. Government legal standards prescribethe 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 towear the front tires at a greater rate compared to the rear tires. Tire rotation is the procedure of moving tires to different car positions, suchas front-to-rear, in order to even out the wear, thereby extending the life of the tire. However care must be taken with unidirectional tires(tires that are designed to rotate in one direction only, for a vehicle that is going forward) so that the correct rotational direction - indicatedon the side wall with an arrow-like symbol - is maintained after the swap.

Wheel alignment

Main article: 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 irregularwear. 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 of camber, caster and toe angles. Thesesettings also affect the handling characteristics of the vehicle.

Retread

Main article: 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 buffingaway the worn tread and applying a new tread.[25] Retreading is economical for truck tires because the cost of replacing the tread is lessthan the price of a new tire. Retreading passenger tires is less economical because the cost of retreading is high compared to the price ofnew 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 theapplication 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-curemethod involves the application of a ready-made tread band on the buffed and prepared casing, which later is cured in an autoclave so thatvulcanization can occur.

During the retreading process, retread technicians must ensure the casing is in the best condition possible to minimize the possibility of acasing failure. Casings with problems such as capped tread, tread separation, unrepairable cuts, corroded belts or sidewall damage, or anyrun-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 orcomfort.[26] The percentage of retread failures should be about the same as for new tire failures, but many drivers, including truckers, areguilty of not maintaining proper air pressure on a regular basis, and, if a tire is abused (overloaded, underinflated, or mismatched to theother tire on a set of duals), then that tire (new or recapped) will fail.[27]

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

Performance characteristicsThe 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

Main article: Tire balance


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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 theorientation of their moment of inertia. This is referred to as balance, imbalance, or unbalance. Tires are checked at the point of manufacturefor excessive static imbalance and dynamic imbalance using automatic tire balance machines. Tires are checked again in the auto assemblyplant or tire retail shop after mounting the tire to the wheel. Assemblies that exhibit excessive imbalance are corrected by applying balanceweights 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 bestpossible match-mounting of the tire/wheel assembly. There are two methods of match-mounting high performance tire to wheel assembliesusing these red (uniformity) or yellow (weight) marks.[28]

Camber thrust

Main article: Camber thrust

Camber thrust and camber force are the force generated perpendicular to the direction of travel of a rolling tire due to its Camber angle andfinite 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 ofrotation. This may cause speedometer error. As the tire diameter grows, the tire width decreases. This centrifugal growth can cause rubbingof the tire against the vehicle at high speeds. Motorcycle tires are often designed with reinforcements aimed at minimizing centrifugalgrowth.[citation needed]

Circle of forces

Main article: 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 avehicle's tire and the road surface.

Contact patch

Main article: 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 betweenthe tire and the road via friction. The length-to-width ratio of the contact patch affects steering and cornering behavior.

Cornering force

Main article: 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 therubber 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 deformed during this cycle. As the rubber deforms and recovers, it imparts cyclical forces into the vehicle. These variations arecollectively referred to as tire uniformity. Tire uniformity is characterized by radial force variation (RFV), lateral force variation (LFV) andtangential force variation. Radial and lateral force variation is measured on a force variation machine at the end of the manufacturingprocess. Tires outside the specified limits for RFV and LFV are rejected. Geometric parameters, including radial runout, lateral runout, andsidewall 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 theforce variation machine used at the factory to grade tire uniformity. This machine can find the best position for the tire on a given wheel sothat the over-all assembly is as round as possible.


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Load sensitivity

Main article: Tire 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 verticalload, Fz, increases.

Pneumatic trail

Main article: 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

Main article: 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

Main article: 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 entersthe contact area and is deformed flat to conform to the roadway. The energy required to make the deformation depends on the inflationpressure, rotating speed, and numerous physical properties of the tire structure, such as spring force and stiffness. Tire makers seek lowerrolling resistance tire constructions to improve fuel economy in cars and especially trucks, where rolling resistance accounts for a highproportion of fuel consumption.

Pneumatic tires also have a much lower rolling resistance than solid tires. Because the internal air pressure acts in all directions, apneumatic tire is able to "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction oftravel, 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 feltwhen propelling wheelchairs or baby buggies fitted with either type so long as the terrain has a significant roughness in relation to the wheeldiameter.[citation needed]

Self aligning torque

Main article: 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

Main article: 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 slightlyshorter 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.[29] Work load ismeasured in ton kilometre per hour (TKPH). The measurement's appellation and units are the same. The recent shortage and increasing costof tires for heavy equipment has made TKPH an important parameter in tire selection and equipment maintenance for the mining industry.


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Tire performance envelope byGoodyear

Tire manufactured in 10th week of 2001

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.[30][31] The rating is based on the weight and speed that the tire can handle withoutoverheating 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 ofthe innermost or outermost ribs. Gravel roads, rocky terrain, and other rough terrain causesaccelerated wear. Over-inflation above the sidewall maximum can cause excessive wear to the centerof the tread. Modern tires have steel belts built in to prevent this. Under-inflation causes excessivewear to the outer ribs. Often, the placard pressure is too low and most tires are under-inflated as aresult.[citation needed] Unbalanced wheels can cause uneven tire wear, as the rotation may not beperfectly circular. Tire manufacturers and car companies have mutually established standards fortread wear testing that include measurement parameters for tread loss profile, lug count, and heel-toewear. 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 ofthe tire footprint and reduce hydroplaning. However, tires with a circular cross-section, such as those found on racing bicycles, whenproperly inflated have a sufficiently small footprint to not be susceptible to hydroplaning. For such tires, it is observed that fully slick tireswill give superior traction on both wet and dry pavement.[32]

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 tireidentification. The DOT Code is mandated by the U.S. Department of Transportation. The DOT Code is useful in identifying tires in aproduct recall.

The DOT Code begins with the letters "DOT" followed by a plant code (two numbers orletters) that identifies where it was manufactured. The last four numbers represent the weekand year the tire was built. A three-digit code was used for tires manufactured before 2000.For example, 178 means it was manufactured in the 17th week of 8th year of the decade. Inthis case it means 1988. For tires manufactured in the 1990s, the same code holds true, butthere is a little triangle () after the DOT code. Thus, a tire manufactured in the 17th weekof 1998 would have the code 178. In 2000, the code was switched to a 4-digit code. Samerules apply, so for example, 3003 means the tire was manufactured in the 30th week of2003.

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 complywith the dimensional, performance and marking requirements of ECE regulation 30. A (lower case) "e" indicates that the tire is certified tocomply with the dimensional, performance and marking requirements of Directive 92/23/EEC. The number in the circle or rectangledenotes the country code of the government that granted the type approval. The last number outside the circle or rectangle is the number ofthe 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 backto the mold of original manufacturer.

Codes

Main article: Tire code


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Studded, highly siped,winter tire

Vehicle applicationsTires are classified into several standard types, based on the type of vehicle they serve. Since the manufacturing process, raw materials, andequipment vary according to the tire type, it is common for tire factories to specialize in one or more tire types. In most markets, factoriesthat manufacture passenger and light truck radial tires are separate and distinct from those that make aircraft or off-the-road (OTR) tires.[citation needed]

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 rubbercompound 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 rubbertread surface area for dry weather performance.[citation needed] The ability to provide a high level of performance on both wet and drypavement varies widely among manufacturers, and even among tire models of the same manufacturer. This is an area of active research anddevelopment, as well as marketing.

Mud and snow

Main article: Snow tires

Mud and Snow, (or M+S, or M&S), is a designation applied rather arbitrarily by manufacturers for all-season and winter tires designed toprovide improved performance under low temperature conditions, compared to summer tires. The tread compound is usually softer than thatused in tires for summer conditions, thus providing better grip on ice and snow, but wears more quickly at higher temperatures. Tires mayhave well above average numbers of sipes in the tread pattern to grip the ice. There are no traction performance requirements which such atire 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 forTesting & Materials. Winter tires will typically also carry the designation MS, M&S, or the words MUD AND SNOW (but see All-seasontires, below).

Some winter tires are fabricated with metal studs (consisting of a tungsten carbide or other hard material pinembedded in a base of a softer metal) for additional traction on icy roads.[33] Between 70 to 80 studs aredriven into a tire to provide better friction between the ice and the soft rubber in winter tires.[34]

The use of studs is restricted in most countries due to the increased road wear that they cause, with thenotable exception of the Nordic countries where they are commonly used during the winter season. Norwayhas implemented fees for using studded tires in some urban areas, and there are a few streets in some of themajor cities in Sweden where studs are not allowed. Typically, studs are never used on heavier vehicles,except for some emergency vehicles like ambulances and fire trucks. Ice resurfacers also use studded tires.The upper tier classes of ice racing[35] and rallying mandates the vehicles be equipped with studded tires.

Other winter tires rely on factors other than studding for traction on ice, e.g. highly porous or hydrophilicrubber that adheres to the wet film on the ice surface. The best stud-less winter tires offer grip close to thatof studded tires during most winter conditions, with the notable exception of blank or polished ice, wherethey cannot match the performance of studded tires. The reason for this is that stud-less winter tires rely onunevenness in the ice surface for their sipes to grab, while studs cut into even the most polished ice surface(and in the process also make it uneven).

Studded tires are also used on bicycles, and the grip advantage on ice is similar to that from using traction sand, with the difference thatthere is no risk of blank spots when using studded tires. Quality tire manufacturers use studs with hard center pins also for bicycle tires, andjust like their automobile counterparts, those studs will continue to protrude from the tire even after many years of usage on bare pavement.There are also low-quality studded bicycle tires being sold that have studs that lack the hard-metal center pin (there is still a center pin, butit is not made of hard metal). Such studs can wear out within a few weeks of cycling on dry pavement.

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 mudto 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


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greater area to prevent the vehicle from sinking too deeply into the mud. However in reasonable amounts of mud and snow, tires should bethinner. Being thinner, the tire will have more pressure on the road surface, thus allowing the tires to penetrate the snow layer and gripharder snow or road surface beneath. This does not compensate when the snow is too deep for such penetration, where the vehicle will sinkinto the snow and plough the snow in front and eventually pack it beneath it until the wheels no longer have traction. In this case, wider tiresare 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 developedfor use under winter conditions. The type of rubber and the tread pattern best suited for use under summer conditions cannot, for technicalreasons, give good performance on snow and ice. The all-season tire is a compromise, and is neither an excellent summer tire nor anexcellent winter tire. They have, however, become ubiquitous as original and replacement equipment on automobiles marketed in theUnited States, due to their convenience and their adequate performance in most situations. Even so, in other parts of the world, likeGermany, 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 aswinter tires but rarely with a snowflake. Owing to the compromise with performance during summer, winter performance is usually poorerthan 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 puncturewhen traveling off-road, the tread pattern offers wider spacing than all-season tires to remove mud from the tread. Many tires in theall-terrain category are designed primarily for on-road use, particularly all-terrain tires that are originally sold with the vehicle.

Spare

Main article: spare tire

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-saverspare" tires are smaller than normal tires to save on trunk/boot space, gas mileage, weight, and cost. Minispares have a short life expectancyand a low speed rating, often below 60 miles per hour (97 km/h).

Light Trailer

Domestic Trailers (including camping trailers) for use on public highways often have different tires than those seen on cars. Often they arebias ply rather than radial tires, and they often don't have as aggressive a tread pattern as standard road tires. They are not built for hightraction in most cases, because in most cases it is not vital that trailer tires have as good a traction as that of the vehicle towing the trailer.

Run-flat

Main article: Run-flat tire

Several innovative designs have been introduced that permit tires to run safely with no air for a limited range at a limited speed. These tirestypically feature strong, load-supporting sidewalls. An infamous example of an alternate run-flat technology has plastic load-bearing insertsattached 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 industrythat 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, dumptrucks, and passenger buses. Truck tires are sub-categorized into specialties according to vehicle position such as steering, drive axle, andtrailer. Each type is designed with the reinforcements, material compounds, and tread patterns that best optimize the tire performance. Arelatively new concept is the use of "Super Singles" or Wide Singles. Generally in a dual configuration, there are 2 tires per position, eachbetween 275 mm-295 mm wide. The Super Single replaces these with a single tire, usually 455 mm wide. This allows for less tread to becontacting 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

Off-the-road (OTR) tires include tires for construction vehicles such as wheel loaders, backhoes, graders, trenchers, and the like; as well as


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Heavy load may require multiple tires

Off-the-road (OTR) tires beingtransported

NASCAR tires

A bicycle tire in the styleof a cruiser

large mining trucks. OTR tires can be of either bias or radialconstruction although the industry is trending towardincreasing use of radial. Bias OTR tires are built with a largenumber of reinforcing plies to withstand severe serviceconditions and high loads.

Dramatically increasing commodity prices has led toshortages of new tires. As a consequence, multi-milliondollar trucks can be idled for lack of tires, costing minesmillions of dollars in lost productivity. This has led to astronger effort to recycle old OTR tires. As of 2008, a newOTR tire can cost up to $50,000; retread tires are sold at half

the price of new tires, and last 80% as long.[36] Retreading an OTR tire is labor intensive. First, theretreading technician must place the old tire in a buffing machine to remove what remains of the oldtread; "skiving" follows this, which is the removal, by hand, of material the buffing misses. Next, thetechnician must inspect the tire, repairing defects. Lastly, the technician fills holes in the tire withrubber, applies a cement gum adhesive, and places the tire on a machine that will apply a new tread.[37]

Agricultural and off-road flotation tires

The agricultural tire classification includes tires used on farm vehicles, typically tractors and specialty vehicles like harvesters. Drivenwheels have very deep, widely spaced lugs to allow the tire to grip soil easily.

For off-road driving in a passenger vehicle, such as in mud, sand, or deep snow, high flotation tires are typically used. Flotation tires are notthe same as M+S tires, as they are designed for low speeds and full-time off road use rather than muddy and snow-covered roads. Flotationtires also help traction in swampy environments and where soil compaction is a concern, featuring large footprints at low inflation pressuresto spread out the area where the rubber meets the ground. Knobby tires are particularly useful where the ground consists of loose particlesthat can be displaced by the knobs. Although the low pressure improves traction in many types of terrain, adjustments may need to be madefor hard surfaces like paved and unpaved roads. Vehicles that use flotation tires for rock climbing are susceptible to flat tires in which thetire pops off the rim, breaking the "bead."

Racing

Racing tires are highly specialized according to vehicle and race track conditions. This classificationincludes tires for drag racing, Auto-x, drifting, Time Attack, Road Racing as well as the large-market race tires for Formula One, IndyCar, NASCAR, V8 Supercars, WRC, MotoGP and the like.Tires are specially engineered for specific race tracks according to surface conditions, corneringloads, and track temperature. Racing tires often are engineered to minimum weight targets, so tiresfor a 500 miles (800 km) race may run only 100 miles (160 km) before a tire change. Some tiremakers invest heavily in race tire development as part of the company's marketing strategy and ameans 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 andconstruction equipment such as skid loaders and fork lift trucks.

Bicycle

Main article: Bicycle tire

This classification includes all forms of bicycle tires, including road racing tires, mountain bike tires, snowtires, 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 requiredfor aircraft increases with the weight of the plane (because the weight of the airplane has to be distributedbetter). Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel


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Changing a tire on a P-3C Orionaircraft

water away to prevent hydroplaning, and for braking effect.

Aircraft tires are usually inflated with nitrogen or helium to minimize expansion and contractionfrom extreme changes in ambient temperature and pressure experienced during flight.[38] Drynitrogen expands at the same rate as other dry atmospheric gases, but common compressed airsources may contain moisture, which increases the expansion rate with temperature.[39] Aircraft tiresgenerally operate at high pressures, up to 200 pounds per square inch (14 bar; 1,400 kPa) forairliners, and even higher for business jets. Tests of airline aircraft tires have shown that they are ableto 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 thecommon content of aircraft tires, to prevent the test room being blown apart by the energy when thetire bursts.

Aircraft tires also include fusible plugs (which are assembled on the inside of the wheels), designed to melt at a certain temperature. Tiresoften overheat if maximum braking is applied during an aborted takeoff or an emergency landing. The fuses provide a safer failure modethat prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surroundingenvironment.

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

Motorcycle

Main article: Motorcycle tyre

There are many different types of motorcycle tires: Sport Touring these tires are generally not used for high cornering loads, but for longstraights, 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 donot 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 patchwhile leaned over. These tires are not recommended for the street by manufacturers, and are known to have a shorter life on the street. Dueto 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 rideon 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 aharder rubber compound and do not provide as much traction as street tires until warmed to a higher internal temperature than street tiresnormally 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 characteristicsMain article: Roadway noise

The design of treads and the interaction of specific tire types with the roadway surface type produces considerable effect upon sound levelsor noise pollution emanating from moving vehicles. These sound intensities increase with higher vehicle speeds.[41] The acoustic intensityproduced varies considerably depending on the tire tread design and the road surface type. There is a study "under development" that aimspredict 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 andregulate transportation safety in the United States of America.

NHTSA


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

UTQGThe Uniform Tire Quality Grading System (UTQG), is a system for comparing the performance of tires, established by the United StatesNational Highway Traffic Safety Administration according to the Code of Federal Regulations 49 CFR 575.104. The UTQG regulationrequires 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 andallied parts. Of particular interest, they published key tire dimension standards, key rim contour dimension standards, key tire valvedimension 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 and valves. It isanalogous to T&RA and ETRTO.

TREAD Act

The Transportation Recall Enhancement, Accountability and Documentation Act (TREAD Act) is a United States federal law that setsstandards 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 automaticidentification.[citation needed] Tags are encoded with various types of manufacturing data, including the manufacturer's name, location ofmanufacture, tire type, manufacturing date, and in some cases test data. RFID transponders can remotely read this data automatically. RFIDtags are used by auto assemblers to identify tires at the point of assembly to the vehicle.[citation needed] Fleet operators utilize RFID as part oftire maintenance operations.

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

SafetyProper vehicle safety requires specific attention to inflation pressure, tread depth, and general condition of the tires. Over-inflated tires runthe risk of explosive decompression (they may pop). On the other hand, under-inflated tires have a higher rolling resistance and suffer fromoverheating and rapid tread wear particularly on the edges of the tread. Excessive tire wear will reduce steering and braking response,[citation needed]

and tires worn down past their safety margins and into the casing run the very real risk of rupturing. Also, certaincombinations 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

Main article: Flat tire

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 lostsufficient 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


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A flat tire

Tire bubble

changed and/or repaired before it becomes completely flat. Continuing to drive a vehicle with a flattire will damage the tire beyond repair, possibly damage the rim and vehicle, and put the occupantsand other vehicles in danger. A flat tire or low-pressure tire should be considered an emergencysituation, requiring immediate attention. Some tires, known as "run-flat tires", have either extremelystiff sidewalls or a resilient filler to allow driving a limited distance while flat, usually at reducedspeed, without permanent damage or hazard.

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

Bubble

Tire bubbles, also referred to as bulges/bumps/protrusions, occur when the sidewall of the tire hasfailed, resulting in a protrusion. Causes of bubbles include having an impact at high speed, overinflation, or poor tire construction/manufacturing. It is generally recommended to replace the tiresince the probability of tire failure has increased. They can occur on the inner or outer sidewall.

Hydroplaning (or aquaplaning)Main article: Hydroplaning (road vehicle)

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

Hydroplaning becomes more prevalent with wider tires (because of the lower weight per contactarea) and especially at higher speeds; it is of virtually no concern to bicycle tires under normal ridingconditions largely because of the lower speeds. The chance of car hydroplaning is also minimal at bicycle speeds as the weight per contactarea 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 tohave similar properties to newly manufactured tires, but rubber degrades over time, and once the vehicle is traveling at high speeds (i.e. on afreeway) the tread could peel off, leading to severe loss of control. In tropical climates, such as Singapore, tires degrade sooner than intemperate climates, and more care should be taken in these climates to ensure that tires do not fail.[citation needed] Also, tires on seldom-usedtrailers 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 tobe removed from service 10 years after the date of manufacture. However, an investigative report by Brian Ross on ABC's 20/20 newsmagazine found that many major retailers such as Goodyear, Wal-Mart, and Sears were selling tires that had been produced six or moreyears 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 holddown tarps. Some facilities are permitted to recycle scrap tires through chipping, and processing into new products, or selling the material tolicensed power plants for fuel. Some tires may also be retreaded for re-use. One group did "a study to evaluate the possibility of using scraptires as a crash cushion system. The objective of this study was to evaluate the material properties of used tires and recycled tire-derivedmaterials 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 processis removing the metal, granulating the rubber and then a chemical process where it is mixed with other usual materials for macadamisedroads. 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.


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A child plays in a playground madefrom recycled tires. Guelph, Canada

Americans generate about 285 million scrap tires per year.[47] Many states have regulations as to thenumber of scrap tires that you may have on site, due to concerns with dumping, fire hazards, andmosquitoes. In the past, millions of tires have been discarded into open fields. This creates abreeding ground for mosquitoes, since the tires often hold water inside and remain warm enough formosquito breeding. Mosquitoes create a nuisance and may increase the likelihood of spreadingdisease. It also creates a fire danger, since such a large tire pile is a lot of fuel. Some tire fires haveburned for months, since water does not adequately penetrate or cool the burning tires. Tires havebeen known to liquefy, releasing hydrocarbons and other contaminants to the ground and evenground water, under extreme heat and temperatures from a fire. The black smoke from a tire firecauses 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 metalsand other contaminants from the tire pieces. Zinc is concentrated (up to 2% by weight) to levels high enough to be highly toxic to aquaticlife and plants.[48] Of particular concern is evidence that some of the compounds that leach from tires into water, contain hormonedisruptors and cause liver lesions.[49]

Asymmetric tireAn asymmetric tire is a kind of specific stabilization method 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--vis its central line, thushaving a distinct inside and outside edge. They may be mounted on either side of the vehicle. Since the tread pattern of many ordinary tiresdo not form symmetry in relation to design or pattern noise, the method of mounting tires is specially prescribed. This type of tires is usedin many cases to promote tire performance, braking performance, and turning performance, since tread contact changes according to thechange 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 thathelp 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 arim cannot be moved to the other side, since the tread pattern will be in the wrong direction. This restricts tire rotation. Some directionaltires 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 stabilizingbelts give a self-aligning torque when a motor vehicle is running straight ahead as well as when it is cornering. However, the sidewalls ofthe 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 thevehicle is being steered positively. The lateral force will be transmitted from the front wheel to the rear of the vehicle, which will tend to besteered off course. Whereas the asymmetric belts bring a gradual change in the lateral displacement of the tire tread corresponding to therim while the cornering load grows. The progressive change will harden the sidewalls to produce an immediate response to steering, whichresults in safer driving.

Other uses

Tires are not desired at landfills, due to their large volumes and 75% void space, which quickly consumes valuable space.[50] Because ofthis, people have found other uses for old tires.

Tire swing

Old tires are sometimes converted into a swing for play. The innovative use allows for an easy way to find a purpose for an existing old tirenot suitable for road use.[51]

Exercise equipment

Used tires are employed as exercise equipment for athletic programs such as American football.[52] One classic conditioning drill that honesplayers' 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 onthe 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 lifttheir feet above the ground higher than normal to avoid tripping.[53]


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Three boys are on a tire swing

Recycling

Main article: Tire recycling

Tires can be recycled into, among other things, the hot melt asphalt, typically as crumb rubbermodifierrecycled asphalt pavement (CRMRAP),[54][55] and as an aggregate in portland cementconcrete[56] Tires can also be recycled into other tires. Tires have also been cut up and used ingarden beds as bark mulch to hold in the water and to prevent weeds from growing. There are some"green" buildings that are being made both private and public buildings that are made from old tires.

Tire Pyrolysis

The pyrolysis method for recycling used tires is a technique which heats whole or shredded tires in a reactor vessel containing an oxygenfree atmosphere and a heat source. In the reactor the rubber is softened after which the rubber polymers continuously break down intosmaller molecules. These smaller molecules eventually vaporize and exit from the reactor. These vapors can be burned directly to producepower or condensed into an oily type liquid, generally used as a fuel. Some molecules are too small to condense. They remain as a gaswhich can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as a solid. When performed well atire pyrolysis process is a very clean operation and has nearly no emissions or waste.[57]

See alsoOutline of tiresDry steeringList of inflatable manufactured goods

References

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^ Global Tire Shipments to Reach 1.7 Billion Units by 2015,According to a New Report by Global Industry Analysts, Inc(http://www.prweb.com/releases/tires_OEM/replacement_tire/prweb4545704.htm)

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^ Goodyear. "New temperature prediction model improves on currentTKPH formula" (http://web.archive.org/web/20061106074110/http://www.goodyear.com/media/pr/pr_2000/22169oh.html). Archivedfrom the original (http://www.goodyear.com/media/pr/pr_2000/22169oh.html) on November 6, 2006. Retrieved October 7, 2007.

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^ M Nehdi, A Khan, (2001). Cementitious Composites ContainingRecycled Tire Rubber: An Overview of Engineering Properties andPotential Applications (http://www.bvsde.paho.org/bvsacd/cd24/cementi.pdf). Cement, Concrete, and Aggregates.

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External linksNational Highway Traffic Safety Adm "Tire Safety" Brochure (http://www.nhtsa.gov/DOT/NHTSA/Vehicle%20Safety/Articles/Associated%20Files/brochure.pdf)U.S. Government tire rating and maintenance site. (http://www.safercar.gov/portal/site/safercar/menuitem.13dd5c887c7e1358fefe0a2f35a67789/?vgnextoid=9f4baa8c16e35110VgnVCM1000002fd17898RCRD)


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