Tyre

Tyre A tyre 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 tyres, especially those fitted to motor vehicles, are manufactured from synthetic rubber; however other materials such as steel may be used.

Firestone tyre

History For most of history wheels had very little in the way of shock absorption and journeys were very bumpy and uncomfortable. The modern tyre 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 tyres. John Boyd Dunlop, a Scottish veterinary surgeon working in Belfast, Ireland, is mainly recognized as the father of the modern tyre, although he was not the first to come up with the idea. In 1845 the first pneumatic (inflatable) tyre 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 tyre. The tyre 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Dunlop re-invented the tyre for his ten year old son's tricycle in 1887 and was awarded a patent for his tyre in 1888 (rescinded 1890). Dunlop's tyre 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 tyre, that tyre was only applied to horse drawn carriages. By Dunlop's time, the bicycle had been fully developed (see Rover) and it proved a far more suitable application for pneumatic tyres. Pneumatic tyres 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 Tyre and Rubber Company. The radial tyre 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 tyre uses parallel carcass plies for the sidewalls and crossed belts for the crown of the

tyre. All modern car tyres are now radial. In 2005, Michelin was reported to be attempting to develop a tyre and wheel combination, the Tweel, which does not use air.

Nomenclature The outer perimeter of the tyre, 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 would be compressed into the grooves by the vehicle's weight, providing better traction in the tyre to road contact. Without such grooves, a layer or film of water would form between the wet roads and the tyre surface, which would cause hydroplaning, substantially reducing traction. However, if the road is dry, they actually reduce grip since they reduce the contact area, hence why 'slicks' are used in motor racing. Traction is especially important for good braking. The depth of these grooves essentially constitutes the tread depth at any time during the lifetime of the car. When the tread on the outer perimeter of the tyre inevitably wears away from use, reducing the tread depth, the tyre should be replaced. The sidewalls are the sections of the tyre which are between the crown and the inner circular edges of the tyre contacting the rim. To avoid tearing at these inner edges, particularly when the tyre is being mounted, there are a number of concentric steel wires buried inside the rubber at both inner edges of the tyre. This inner rim is called the bead. Pneumatic tyres generally have reinforcing threads in them; based on the orientation of the threads, they are classified as bias-ply/cross ply or radial. Tyres with radial yarns (known as radial tyres) are standard for almost all modern automobiles.

Tyre types Pneumatic tyres Air-filled tyres are known as pneumatic tyres, and these are the type in almost universal use today. Pneumatic tyres are made of a flexible elastic material such as rubber with reinforcing threads/wires inside the elastic material. The air compresses as the wheel goes over a bump and acts as a shock absorber. Tyres are inflated through a valve, typically a Schrader valve on automobiles and most bicycle tyres, or a Presta valve on high performance bicycles. Attempts have been made to make various types of solid tyre but none has so far met with much success. The air in conventional pneumatic tyres acts as a near constant rate spring because the decrease in the tyre's volume as the tyre compresses over a bump is minimal. "Airless" tyres 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 tyre and the effective spring rate rises sharply as the tyre compresses. The result is a tyre which is less forgiving, particularly with regards to sharp transient bumps and provides poor ride and handling characteristics. The "steering feel" of such tyres is also different from that of pneumatic tyres, as their solidity does not allow the amount of torsion that exists in the carcass of a pneumatic tyre 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 tyres which are much more robust and immune to puncture. The common motor vehicle tyre is mounted around a steel or aluminium alloy wheel at service stations or repair shops for vehicles using a special tyre mounting apparatus while the wheel is off the vehicle. After mounting, the tyre is inflated (pressurized) with air through the valve stem to manufacturer's specified pressure, which is more than atmospheric pressure. The wheel and tyre assembly are then attached to the vehicle through a number of holes in the wheel using lug nuts. Because tyres are often not made with perfectly even mass all around the tyre, a special tyre-balancing apparatus at a repair shop spins the wheel with the tyre to determine where small weights should be attached to the outer edge of the rim to balance out the wheel. Such tyre balancing with these kinds of weights avoids vibration when the vehicle is driven at higher speeds. With the introduction of radial tyres, 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 tyre lends itself to the problems of variation in stiffness around the tyre. 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. Tyres outside the specified limits for RFV and LFV are rejected. This is known in general throughout the industry as Tyre Uniformity.

Automobile and truck tyres New automotive tyres now also have ratings for traction, tread wear, and temperature resistance (collectively known as UTQG ratings); as well as speed and load ratings. Some tread designs are unidirectional and the tyre has a rotation direction indicated by an arrow showing which way the tyre should rotate when the vehicle is moving forwards. It is important not to put a 'clockwise' tyre on the left hand side of the car or a 'counterclockwise' tyre on the right side. Tyre rotation moves tyres between the different wheels of the vehicle as front and back axles carry different loads and thus the tyres wear differently. Tyre tread gauges are small rulers designed to be inserted into tyre 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). Wear bars may be designed into the tyre tread to indicate when it is time to replace the tyre. Essentially, part of the tyre tread is shallower than the rest and will show when the tyre is worn down to that level. There is currently an attempt to reinforce the tyre with nanomaterial. This is likely to increase the tyre 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 tyres

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Performance (and racing) tyres o Performance tyres 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 tread wear rating. o Performance street tyres 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 tyre models of the same manufacturer, and is a highly active area for research and development, as well as marketing. o The ultimate variant of performance tyre has no tread pattern at all and is called a slick tyre. Slick tyres 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. o R compound tyres, similar to cheater slicks, are technically approved by the DOT as street legal, but are in fact designed for racing, with minimal tread and ultra soft rubber. They can typically be distinguished by very low tread wear rating. o The highest performance tyres actually designed to be driven on the street are often called summer or three-season tyres, 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 tyres, if the vehicle is to be driven much in the winter.

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Winter (snow and ice) tyres o Winter tyres are designed to provide improved performance under winter conditions compared to tyres made for use in summer. The rubber compound used in the tread of the tyre is usually softer than that used in tyres for summer conditions, so providing better grip on ice and snow, but wearing more quickly at higher temperatures. Winter tyres often have fine grooves and sipping in the tread patterns that are designed to grip any unevenness on ice. Winter tyres are usually removed for storage in the spring, because the rubber compound becomes too soft in warm weather resulting in a reduced tyre life. o According to California Vehicle Code Section 558, "A 'Snow-tread tyre' is a tyre which has a relatively deep and aggressive tread pattern compared with conventional passenger tread pattern".

Dedicated winter tyres will bear the "Mountain/Snowflake Pictograph" if designated as a winter/snow tyre by the American Society for Testing & Materials. Winter tyres will typically also carry the designation MS, M/S, M+S, M&S, or the words MUD AND SNOW (but see All-season tyres, below) o Many winter tyres 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 tyres. Use of studs is regulated in most countries, and even prohibited in some countries due to the increased road wear caused by studs. o Other winter tyres 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. o Some jurisdictions may from time to time require snow tyres or traction aids (e.g. tyre chains) on vehicles driven in certain areas during extreme conditions. All-season tyres o These are an attempt to make a tyre that will be a compromise between a tyre developed for use on dry and wet roads during summer, and a tyre 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 tyre is therefore a compromise, and is neither an excellent summer tyre, nor an excellent winter tyre. 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. o All-Season tyres are also marked for mud and snow (e.g. M+S, M&S, etc.) the same as winter tyres. However, due to the compromise with performance during summer, winter performance is usually not comparable with a winter tyre. Run flat tyres All-terrain tyres o All-terrain tyres are typically used on SUVs and light trucks. These tyres often have stiffer sidewalls for greater resistance against puncture when travelling off-road; the tread pattern offers wider spacing than all-season tyres to evacuate mud from the tread. o Within the all-terrain category, many of the tyres available are designed primarily for on-road use, particularly all-terrain tyres that are originally sold with the vehicle. Mud tyres o Mud terrain tyres 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. o

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Mud terrain tyres also tend to be wider than other tyres, 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 tyres 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 tyres tend to tear and chip on roads, because they are made from hard rubber compounds that do not bend easily. Mud tyres are also marked for mud and snow (e.g. M+S, M&S, etc.) the same as winter tyres.

Tyre manufacturing & maintenance Some tyre manufacturing companies • • • • • • • • •

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Bridgestone o Firestone Continental Cooper Dunlop Goodyear Kelly Springfield Tyre and Rubber Company Kumho Michelin MRF Tyres o B.F. Goodrich o Uniroyal o Pirelli Nokian Tyres Toyo Yokohama

Maintenance of automobile tyres Friction from moving contact with the road causes the tread on the outer perimeter of the tyre to eventually wear away. When the tyre tread becomes too shallow, the tyre is worn out and should be replaced. The same tyre rims can usually be used throughout the lifetime of the car. Uneven or accelerated tyre wear can be caused by bad wheel alignment. More wear on a tyre 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 tyre is said to be bald. A bald tyre should be replaced as soon as possible. Sometimes tyres with worn tread are recapped; i.e. a new layer of rubber with grooves is bonded onto the outer perimeter

of a worn tyre. Because this bonding may occasionally come loose on the tyre, new tyres are superior to recapped tyres. Sometimes a pneumatic tyre gets a hole or a leak through which the air inside leaks out resulting in a flat tyre, 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 tyre edge is not perfect. Many leaks in flat tyres, though, are caused by nails, screws, caltrops, broken glass or other sharp objects puncturing the rubber tyre wall. If the hole is small and not elongated, the tyre can often be repaired by using plugs from a tyre repair kit. A leak in a tyre can often be found by submerging the tyre, pressurized with air, under water to see where air bubbles come out. If submerging a tyre underwater is not possible, the leak can be searched for by covering the pressurized tyre 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 tyre 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 tyre also, particularly if a hole is too elongated for a simple plug. Tyre repair with such patches requires the tyre to be taken off the rim and then remounted after the patch is applied. Sometimes a more serious rupture of the tyre material occurs resulting in a blow-out. The damaged tyre 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 tyre will have to be taken off the rim and remounted after the valve replacement. Occasionally, other types of damage require replacement of a tyre. Vehicles typically carry a spare tyre, already mounted on a rim, to be used in case a flat tyre or blow-out occurs. These days, most spare tyres (sometimes called "doughnuts") for cars are smaller than normal tyres (to save on trunk space, gas mileage, and cost) and should not be driven very far before replacement with a full-size tyre. Years ago, full-size or conventional spare tyres were used. A few modern vehicle models may use conventional spare tyres also. Jacks and tyre irons for emergency replacement of a flat tyre with a spare tyre are included when buying a new car. Not included, but sometimes available separately, are hand or foot pumps for filling a tyre with air by the vehicle owner. Cans of pressurized "gas" can sometimes be bought separately for convenient emergency refill of a tyre. Alternatively, many modern cars and trucks are equipped with run flat tyres that may be driven with a puncture - or perhaps are even self-repairing for moderate sized holes. Front tyres, especially on front wheel drive vehicles, have a tendency to wear out more quickly than rear tyres. Routine maintenance including tyre rotation, exchanging the front and rear tyres with each other, is often done periodically to even out tyre wear. There are simple hand-held tyre-pressure gauges which can be temporarily attached to the valve stem to check a tyre's interior air pressure. Because of slow leaks or changes in weather

or other conditions, tyre 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 tyres, with too much wear to be safe on vehicles or cannot be repaired 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 tyres are kept, often in a constant state of legal antagonism with the municipal authorities. Although tyres 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 tyres such a problem also make them one of the most re-used waste materials, as the rubber is very resilient and can be reused in other products; it also yields much energy when burned under controlled conditions. Recapped tyres used to be very common, particularly in the trucking industry; the rubber tread of a tyre 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 tyre 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 tyres. With the advances in tyre technology leading to longer tread life and the changes in the relative economics of raw materials and labour, this is no longer economically advantageous for automobile tyres. While salvaged tyres make cheap toys which can be used variously for pets, animals in captivity or human children, e.g. the ubiquitous "tyre 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 tyres. Since 1989, when only 10 percent of scrap tyres were recycled or reused, the United States significantly increased its tyre reclamation efforts to slightly more than 80 percent. In 2003, tyre reclamation looked like this: • • •

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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

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9 million were sent to other countries, where they are used to make retreads

In addition to the 290 million scrap tyres, 16.5 million used tyres in the US are given new temporary life as retreads. Because of safety issues, new tyres must be manufactured primarily from virgin rubber, however, with recycled rubber making up only 5 to 15 percent of the finished product. Furthermore tyre strips are used as a severe instrument for punitive flagellation, which leaves dark bruises.