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Tires

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A tyre or tire is a device covering the circumference of a wheel. It is an essential part of most ground vehicles and is used to dampen the oscillations caused by irregularities in the road surface, to protect the wheel from wear and tear as well as to provide a high-friction bond between the car and the road to improve acceleration and handling. Today most tires, especially those fitted to motor vehicles, are manufactured from synthetic rubber, however other materials such as steel may be used.

Firestone tire
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Firestone tire

Contents

History

A tire repair shop in Vologda, Russia. The text painted says "Tire mounting" (Shinomontazh)
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A tire repair shop in Vologda, Russia. The text painted says "Tire mounting" (Shinomontazh)

For most of history wheels had very little in the way of shock absorption and journeys were very bumpy and uncomfortable. The modern tire came about in stages in the 19th century.

In 1844, Charles Goodyear invented vulcanization, the process that would later be used to produce cured rubber tires.

John Boyd Dunlop, a Scottish veterinary surgeon working in Belfast, Ireland, is mainly recognized as the father of the modern tire, although he was not the first to come up with the idea. In 1845 the first pneumatic (inflatable) tire was patented by fellow Scotsman, the engineer Robert William Thomson, born in Stonehaven, Scotland, as the Aerial Wheel. This invention consisted of a canvas inner tube surrounded by a leather outer tire. The tire gave a good ride, but there were so many manufacturing and fitting problems that the idea had to be abandoned. John Dunlop re-invented the tire for his ten year old son's tricycle in 1887 and was awarded a patent for his tire in 1888 (rescinded 1890). Dunlop's tire had a modified leather hosepipe as an inner tube and rubber treads. It wasn't long before rubber inner tubes were invented.

Because neither bicycles nor automobiles had been invented when Thomson produced his tire, that tire was only applied to horse drawn carriages. By Dunlop's time, the bicycle had been fully developed (see Land Rover) and it proved a far more suitable application for pneumatic tires. Pneumatic tires were first installed on aircraft in 1906.

Dunlop partnered with William Harvey du Cros to form a company which later became the Dunlop Rubber Company to produce his invention. The invention quickly caught on for bicycles and was later adapted for use on cars. Dunlop is now a subsidiary of the Goodyear Tire and Rubber Company.


The radial tire was invented by Michelin, a French company, in 1946, but did not see wide use in the United States, the largest market at that time, until the 1970s. This type of tire uses parallel carcass plies for the sidewalls and crossed belts for the crown of the tire. All modern car tires are now radial. In 2005, Michelin was reported to be attempting to develop a tire and wheel combination, the Tweel, which does not use air.

Etymology

According to the Oxford English Dictionary, quoted in Fowler's Modern English Usage, the word is a shortening of attire, and the British spelling tyre is a recent divergence from historical tradition. Fowler also notes that the altered spelling tyre originally met with resistance from conservative British institutions such as The Times newspaper.

Nomenclature

The outer perimeter of the tire, often called the crown, has various designs of jagged shaped grooves in it, known as the tread. These grooves are especially useful during weather with rain (or snow). The water from the rain is compressed into the grooves by the vehicle's weight, providing better traction in the tire-to-road contact. Without such grooves, a layer or film of water would form between the wet road and the tire's surface, which would cause hydroplaning, substantially reducing traction. However, if the road is dry, treads actually reduce grip since they reduce the contact area, hence why 'slicks' are used in motor racing. Traction is especially important to achieve good braking or high-speed cornering. The depth of these grooves essentially constitutes the tread depth. Varying due to wear during the lifetime of the car. When the tread on the outer perimeter of the tire wears away, reducing the tread depth, the tire should be replaced. The sidewalls are the sections of the tire which are between the crown and the inner circular edges of the tire contacting the rim. To avoid tearing at these inner edges, particularly when the tire is being mounted, there are a number of concentric steel wires buried inside the rubber at both inner edges of the tire. This inner rim is called the bead.

Some air-filled tires, especially those used with spoked wheels such as on bicycles, or on vehicles travelling on rough roads, have an inner tube; this was also formerly the case of automobile tires. This is a fully sealed rubber tube with a valve to control flow of air in and out. Others, including modern radial tires, use a seal between the metal wheel and the tire to maintain the internal air pressure (tubeless tire). This method, however, tends to fail desperately if the vehicle is used on rough roads as a small bend on the rim (metal wheel) will result in deflation. The inner tubes are usually made of halobutyl rubber, because of its suitable mechanical properties and excellent impermeability for air.

Pneumatic tires generally have reinforcing threads in them; based on the orientation of the threads, they are classified as bias-ply/cross ply or radial. Tires with radial yarns (known as radial tires) are standard for almost all modern automobiles.

Tire types

Wagon tires

The earliest tires were hoops of metal placed around wagon wheels. The tire was heated in a forge, placed on the wheel and quenched, causing the metal to shrink, which drew the rim against the spokes and provided stiffness to the wheel. This work was done by a wheelwright, a craftsman who specialized in making wagon wheels.

Pneumatic tires

Air-filled tires are known as pneumatic tires, and these are the type in almost universal use today. Pneumatic tires are made of a flexible elastomer material such as rubber with reinforcing threads/wires inside the elastomer material. The air compresses as the wheel goes over a bump and acts as a shock absorber. Tires are inflated through a valve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve on high performance bicycles. Attempts have been made to make various types of solid tire but none has so far met with much success. The air in conventional pneumatic tires acts as a near constant rate spring because the decrease in the tire's volume as the tire compresses over a bump is minimal. "Airless" tires usually employ a type of foam or sponge like construction which consists of a large number of small air filled cells. As a result compression is localised within the tire and the effective spring rate rises sharply as the tire compresses. The result is a tire which is less forgiving, particularly with regards to sharp transient bumps and provides poor ride and handling characteristics. The "steering feel" of such tires is also different from that of pneumatic tires, as their solidity does not allow the amount of torsion that exists in the carcass of a pneumatic tire under steering forces, and the resultant sensory feedback through the steering apparatus; as a result they feel as if they are pivoting on bearings at the contact point. They are more popular for bicycles than for automobiles, which have tires which are much more robust and immune to puncture.

The common motor vehicle tire is mounted around a steel or aluminum alloy wheel at service stations or repair shops for vehicles using a special tire mounting apparatus while the wheel is off the vehicle. After mounting, the tire is inflated (pressurized) with air through the valve stem to manufacturer's specified pressure, which is more than atmospheric pressure. The wheel and tire assembly are then attached to the vehicle through a number of holes in the wheel using lug nuts. Because tires are often not made with perfectly even mass all around the tire, a special tire-balancing apparatus at a repair shop spins the wheel with the tire to determine where small weights should be attached to the outer edge of the rim to balance out the wheel. Such tire balancing with these kind of weights avoids vibration when the vehicle is driven at higher speeds.

With the introduction of radial tires, however, it was found that some vibrations could not be cured by adding balance weights. This was because the structure and manufacture of a radial tire lends itself to the problems of variation in stiffnes around the tire. These variations are measured as Radial Force Variation and Lateral Force Variation, which are measured on a Force Variation Machine at the end of the manufacturing process. Tires outside the specified limits for RFV and LFV are rejected. This is known in general throughout the industry as "Tire Uniformity."

Automobile and truck tires

Automobile tires have numerous rating systems.

New automotive tires now also have ratings for traction, treadwear, and temperature resistance (collectively known as UTQG ratings); as well as speed and load ratings.

Some tread designs are unidirectional and the tire has a rotation direction indicated by an arrow showing which way the tire should rotate when the vehicle is moving forwards. It is important not to put a 'clockwise' tire on the left hand side of the car or a 'counter-clockwise' tire on the right side. Tire rotation moves tires between the different wheels of the vehicle as front and back axles carry different loads and thus the tires wear differently.

Tire tread gauges are small rulers designed to be inserted into tire treads to measure the remaining tread depth. Local legislation may specify minimum tread depths, typically between 1/8" (3.2 mm) and 1/32" (0.8 mm). Wearbars may be designed into the tire tread to indicate when it is time to replace the tire. Essentially, part of the tire tread is shallower than the rest and will show when the tire is worn down to that level.

There is currently an attempt to reinforce the tire with nanomaterial. This is likely to increase the tire life, but may turn out to be a bad idea if the worn out part of nanocarbon deposited on the roads is washed off and ends up in the food chain.

Types of automobile tires

  • Performance (and racing) tires
    • Performance tires tend to be designed for use at higher speeds. They often have a softer rubber compound for improved traction, especially on high speed cornering. The trade off of this softer rubber is a lower treadwear rating.
    • Performance street tires sometimes sacrifice wet weather handling by having shallower water channels to provide more actual rubber treat surface area for dry weather performance; the ability to provide both high levels of performance on both wet and dry pavement varies widely between manufacturer and even tire models of the same manufacturer, and is a highly active area for research and development, as well as marketing.
    • The ultimate variant of performance tire has no tread pattern at all and is called a slick tire. Slick tires are not legal for use on public roads in most jurisdictions due to their extremely poor wet weather characteristics, but cheater slicks which circumvent the literal wording of the law, if not the intent, are available.
    • R compound tires, similar to cheater slicks, are technically approved by the DOT as street legal, but are in fact designed for racing, with minimal tread and ultrasoft rubber. They can typically be distinguished by very low treadwear rating.
    • The highest performance tires actually designed to be driven on the street are often called summer or three-season tires, since they are optimized for ultimate warm weather wet and dry performance at the expense of snow and ice traction; they therefore must be replaced with winter or all-season tires, if the vehicle is to be driven much in the winter.
Bicycle winter tire.
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Bicycle winter tire.
  • Winter (snow and ice) tires
    • Winter tires are designed to provide improved performance under winter conditions compared to tires made for use in summer. The rubber compound used in the tread of the tire is usually softer than that used in tires for summer conditions, so providing better grip on ice and snow, but wearing more quickly at higher temperatures. Winter tires often have fine grooves and siping in the tread patterns that are designed to grip any unevenness on ice. Winter tires are usually removed for storage in the spring, because the rubber compound becomes too soft in warm weather resulting in a reduced tire life.
    • According to California Vehicle Code Section 558, "A 'Snow-tread tire' is a tire which has a relatively deep and aggressive tread pattern compared with conventional passenger tread pattern".
    • Dedicated winter tires will bear the "Mountain/Snowflake Pictograph" if designated as a winter/snow tire by the American Society for Testing & Materials. Winter tires will typically also carry the designation MS, M/S, M+S, M&S, or the words MUD AND SNOW (but see All-season tires, below)
    • Many winter tires are designed to be studded for additional traction on icy roads. The studs also roughen the ice, so providing better friction between the ice and the soft rubber in winter tires. Use of studs is regulated in most countries, and even prohibited in some countries due to the increased road wear caused by studs.
    • Other winter tires rely on factors other than studding for traction on ice, e.g. highly porous or hydrophilic rubber which adheres to the wet film on the ice surface.
    • Some jurisdictions may from time to time require snow tires or traction aids (e.g. tire chains) on vehicles driven in certain areas during extreme conditions.
  • All-season tires
    • These are an attempt to make a tire that will be a compromise between a tire developed for use on dry and wet roads during summer, and a tire developed for use under winter conditions, when there is snow and ice on the road. However, the type of rubber and the tread pattern best suited for use under summer conditions cannot, for technical reasons, give good performance on snow and ice. The all-season tire is therefore a compromise, and is neither an excellent summer tire, nor an excellent winter tire. They have, however, become almost ubiquitous as original and replacement equipment on automobiles marketed in the United States, due to their convenience and their adequate performance in most situations.
    • All-Season tires are also marked for mud and snow (e.g. M+S, M&S, etc.) the same as winter tires. However, due to the compromise with performance during summer, winter performance is usually not comparable with a winter tire.
  • Run flat tires
  • All-terrain tires
    • All-terrain tires are typically used on SUVs and light trucks. These tires often have stiffer sidewalls for greater resistance against puncture when traveling off-road, the tread pattern offers wider spacing than all-season tires to evacuate mud from the tread.
    • Within the all-terrain category, many of the tires available are designed primarily for on-road use, particularly all-terrain tires that are originally sold with the vehicle.
  • Mud tires
    • Mud terrain tires are characterized by large, chunky tread patterns designed to bite into muddy surfaces and provide grip. The large open design also allows mud to clear more quickly from between the lugs.
    • Mud terrain tires also tend to be wider than other tires, to spread the weight of the vehicle over a greater contact patch to prevent the vehicle from sinking too deep into the mud.
    • Depending on the composition and tread pattern, many mud terrain tires are not well suited to on-road use. They can be noisy at highway speeds, and due to the open tread design, they have less of a contact area with the road, limiting traction. The large lugs on mud tires tend to tear and chip on roads, because they are made from hard rubber compounds that do not bend easily.
    • Mud tires are also marked for mud and snow (e.g. M+S, M&S, etc.) the same as winter tires.

Railway tires

Steel tire on a steam locomotive's driving wheel is heated with gas flames to expand and loosen it so it may be removed and replaced.
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Steel tire on a steam locomotive's driving wheel is heated with gas flames to expand and loosen it so it may be removed and replaced.

The steel wheels of railway cars are fitted with tires which are themselves usually made of steel.

(Some trains, mostly certain types of metros and people movers, have rubber tires, including some lines of the Paris M├ętro, the Mexico City Metro, the Caracas Metro, the Montreal Metro, and the Santiago Metro).

As efficient as the rolling of a steel wheel on a steel rail is, wear still takes place - on acceleration, on braking, and on cornering. As well as the simple wearing away of the wheel surface, a wheel that wears begins to deviate from the correct profile. The shape of a train wheel is designed and specified precisely for the best possible riding and cornering characteristics, and too much wear can alter that. Wear can also take place unevenly if wheels lock up under heavy braking, causing flat spots.

Another different form of damage to a train's wheels takes place if violent wheelslip occurs. The friction so caused can heat the wheel (and rail) enough to cause permanent heat damage.

Replacing a whole wheel because of a worn contact surface proves expensive, so the concept of fitting steel tires to train wheels came about. The tire is a hoop of steel that is fitted around the steel or iron wheel. No obvious form of fastening is generally used to attach it. As with wagon wheels, the tire is held by an interference fit - it is made slightly smaller than the wheel on which it is supposed to fit. To fit a tire, it is heated up until it is glowing hot. Railroad workshops generally have special equipment to do so. As the tire heats, it expands, making it big enough to fit around the wheel. After placing it on the wheel, the tire is cooled, and it shrink fits onto the wheel. When cold, friction between the tire and the wheel is such that the tire will not budge even under quite extreme forces.

Removing a tire is done in reverse - the tire is heated while on the wheel until it loosens.

Tires are reasonably thick, up to about an inch thick or more, giving plenty of room to wear. If a tire wears out of shape, or gets flat-spotted, but has a reasonable amount of metal left, it can be turned on a wheel lathe to refinish it, reshaping it to the correct profile.

Tire manufacturing & maintenance

See: Tire manufacturing.

Some tire manufacturing companies

Maintenance of automobile tires

Friction from moving contact with the road causes the tread on the outer perimeter of the tire to eventually wear away. When the tire tread becomes too shallow, the tire is considered worn out and should be replaced. The same tire rims can usually be used throughout the lifetime of the car. Uneven or accelerated tire wear can be caused by bad wheel alignment. More wear on a tire facing the outside or the inside of a car is often a sign of bad wheel alignment. When the tread is worn away completely and especially when the wear on the outer rubber exposes the reinforcing threads inside them, the tire is said to be bald. A bald tire should be replaced as soon as possible. Sometimes tires with worn tread are recapped, i. e. a new layer of rubber with grooves is bonded onto the outer perimeter of a worn tire. Because this bonding may occasionally come loose on the tire, new tires are superior to recapped tires.

Sometimes a pneumatic tire gets a hole or a leak through which the air inside leaks out resulting in a flat tire, a condition which must be fixed before the car can be driven further safely. A leak may be slow in a few cases, such as is sometimes observed when the seal between the rim and tire edge is not perfect. Many leaks in flat tires, though, are caused by nails, screws, caltrops, broken glass or other sharp objects puncturing the rubber tire wall. If the hole is small and not elongated, the tire can often be repaired by using plugs from a tire repair kit. A leak in a tire can often be found by submerging the tire, pressurized with air, under water to see where air bubbles come out. If submerging a tire underwater is not possible, the leak can be searched for by covering the pressurized tire surface with a soapy solution to see where leaking air forms soap bubbles. A puncturing object, such as a nail or a screw, can be pulled out using pliers. Then a plug coated with a semi-liquid form of rubber can be inserted into the hole with a special tool. The rubber covering the plug solidifies rather quickly, after which the protruding ends of the plug can be cut off, the tire can be refilled with air to the appropriate pressure, and the repaired wheel replaced on the vehicle. Patches covering a hole have been glued or rubber-cemented to the interior surface of a tire also, particularly if a hole is too elongated for a simple plug. Tire repair with such patches requires the tire to be taken off the rim and then remounted after the patch is applied. Sometimes a more serious rupture of the tire material occurs resulting in a blowout. The damaged tire typically must be replaced after that. A leaking valve stem may occasionally be the cause of a leak, necessitating valve stem replacement. This replacement means the tire will have to be taken off the rim and remounted after the valve replacement. Occasionally, other types of damage require replacement of a tire.

Vehicles typically carry a spare tire, already mounted on a rim, to be used in case a flat tire or blowout occurs. These days, most spare tires (sometimes called "doughnuts") for cars are smaller than normal tires (to save on trunk space, gas mileage, and cost) and should not be driven very far before replacement with a full-size tire. Years ago, full-size or conventional spare tires were used. A few modern vehicle models may use conventional spare tires also. Jacks and tire irons for emergency replacement of a flat tire with a spare tire are included when buying a new car. Not included, but sometimes available separately, are hand or foot pumps for filling a tire with air by the vehicle owner. Cans of pressurized "gas" can sometimes be bought separately for convenient emergency refill of a tire.

Alternatively, many modern cars and trucks are equipped with run flat tires that may be driven with a puncture - or perhaps are even self-repairing for moderate sized holes.

Front tires, especially on front wheel drive vehicles, have a tendency to wear out more quickly than rear tires. Routine maintenance including tire rotation, exchanging the front and rear tires with each other, is often done periodically to even out tire wear. There are simple hand-held tire-pressure gauges which can be temporarily attached to the valve stem to check a tire's interior air pressure. Because of slow leaks or changes in weather or other conditions, tire pressure may occasionally have to be adjusted, usually by refilling through the valve stem with some pressurized air which is often available at service stations.

Other use and recycling

Used tires, with too much wear to be safe on vehicles or unrepairable punctures, are among the largest and most problematic sources of waste, due to the large volume produced and their durability. Municipal trash haulers will usually not accept them. Most heavily populated areas contain specific dumps where huge piles of literally millions of discarded tires are kept, often in a constant state of legal antagonism with the municipal authorities. Although tires themselves are not considered hazardous waste, these dumps sometimes catch fire and may burn for months before they can finally be extinguished, creating enormous volumes of toxic air pollution, oil, and heavy metals. Some such fires have become Superfund cleanup sites.

Ironically, those same characteristics which make waste tires such a problem also make them one of the most re-used waste materials, as the rubber is very resilient and can be resued in other products; it also yields much energy when burned under controlled conditions.

Retreadded or recapped tires used to be very common, particularly in the trucking industry; the rubber tread of a tire would wear off long before the carcass, consisting of the fabric plies, sidewalls, and beads, was no longer usable, and therefore good carcasses were simply overlaid with another tread and returned to service. Since the tread is attached in the same way as with a new carcass, such a tire is as reliable as a new one; in fact usually more so, since each individual used carcass is inspected, which is not the case when constructing new tires. With the advances in tire technology leading to longer tread life and the changes in the relative economics of raw materials and labor, this is no longer economically advantageous for automobile tires.

While salvaged tires make cheap toys which can be used variously for pets, animals in captivity or human children, e.g. the ubiquitous "tire swing", they can also be deliberately torn apart to re-use the rubber. According to the US Environmental Protection Agency, every year Americans discard approximately 290 million automobile and truck used tires. Since 1989, when only 10 percent of scrap tires were recycled or reused, the United States significantly increased its tire reclamation efforts to slightly more than 80 percent. In 2003, tire reclamation looked like this:

  • 130 million were used as fuel
  • 56 million were recycled or used in civil engineering projects
  • 27.5 million were recycled into other products or projects; for example, rubber lumber, stall mats for horses, roof pads, sports mats, shower tiles, truck bed mats, and commercial flooring
  • 12 million were ground up and used in rubber-modified asphalt for roads and athletic tracks
  • 9 million were sent to other countries, where they are used to make retreads

In addition to the 290 million scrap tires, 16.5 million used tires in the US are given new temporary life as retreads.

Because of safety issues, new tires must be manufactured primarily from virgin rubber, however, with recycled rubber making up only 5 to 15 percent of the finished product.

Furthermore tire strips are used as a severe instrument for punitive flagellation, which leaves dark bruises.

Mulches made from old tires have become available on the market for individual or industrial agricultural or horticultural use, either as loose pieces mimicking shredded wood, or in sheets of such pieces loosely adhered, for use as walkways, edging, tree rings, stepping stones. Both types of product are also marketed as excellent ground material for playgrounds, being longer lasting and more forgiving that the usual materials used, e.g. sand, gravel, or shredded wood or bark. Although the materials are extremely resistant to environmental breakdown and essentially last forever, the possibility of whether toxic agents, especially heavy metals, do leach out and possibly contaminate soil, particularly where food crops are grown, is currently under investigation.

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See also

Sources and References - External Links

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