Tire

From Wikipedia, the free encyclopedia

A tire or tyre (see spelling differences) 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 vehicle and the ground to improve acceleration and handling.

Today most tires, especially those fitted to motor vehicles, are manufactured from synthetic rubber or rubber composites, but other materials such as steel may be used for strength in the tire.

Contents 1 History 2 Nomenclature 3 Tire physics 4 Treads and tire wear 5 Tire types 5.1 Wagon tires 5.2 Pneumatic tires 5.2.1 Automobile and truck tires 5.2.1.1 Types of automobile tires 5.2.2 Ratings 5.3 Aviation tires 5.4 Railway tires 5.5 Maintenance and safety of automobile tires 6 Tire manufacturing 6.1 Notable tire manufacturing companies 7 Other use and recycling 8 See also 9 References 10 External links

[edit] History

The ancient Mayans are now believed to have used processes similar to vulcanization [[1]], but only in 1844 did Charles Goodyear invent vulcanization, which would later be used to produce cured rubber tires.

John Boyd Dunlop, a Scottish veterinary surgeon, is mainly recognized as the father of the modern tire.

In 1845 the first pneumatic (inflatable) tire was patented by Robert William Thomson.

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Dunlop re-invented the tire for his ten year old son's tricycle in 1887 and was awarded a patent for his tire in 1888 (rescinded 1890). 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 in 1946, but did not see wide use in the United States, the largest market at that time, until the 1970s.

In 2005, Michelin was reported to be attempting to develop a tire and wheel combination, the Tweel, which does not use air. [2]

[edit] 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 rain or snow. The water from the rain is compressed into the grooves by the vehicle's weight, providing better traction at the tire-to-road contact. 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. The tire is a very complicated material.

Some air-filled tires, especially those used with Wire wheels such as on bicycles and motorcycles, 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 tires). This method, however, tends to fail 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, whereas bias-ply tires are the norm for trailers.

[edit] Tire physics

The amount of traction a tire can deliver depends on a large number of factors:

• The construction of the tire affects its effective traction - stiff-walled tires (such as run flat tires) behave differently from those with more flexible side-walls.
• The type of surface that the tire is on (wet or dry road, concrete, asphalt, dirt, sand, etc). The coefficient of friction for normal road tires varies between about 0.7 and 0.4 on dry and wet pavement, respectively.
• The kind of rubber it is made from - the composition of the tread compounds. Soft rubber molds to the shape of small undulations in the road better than harder compounds and therefore grips better. However, soft rubber also wears out more rapidly than hard rubber so there is a difficult compromise to be made in designing the ideal rubber for a particular application.
• How hot the rubber is affects how 'sticky' it is. This is why the pit crews in a Formula 1 race team will keep spare tires in special heated blankets in readiness for a pit stop. Race drivers will sometimes deliberately slide their cars from side to side to try to heat up the tires prior to the start of a race.
• The tread pattern of the tire can also make a big difference. In terms of grip, a bald tire (or a deliberately smooth racing 'slick') has good grip on dry pavement, while the same tire on the same pavement but in wet conditions has poor grip. On the other hand, in wet conditions, a patterned tire allows water to be squeezed out from under the part of the tread that's in contact with the road into the grooves between the treads. This allows more of the rubber to be in contact with the road providing more grip. But in dry conditions its traction is not as good as a smooth tire because the grooves on its surface decrease the tire's contact area. Different tread patterns offer different compromises between wet and dry handling. Specialised treads for winter conditions - or off-road driving further complicate matters.
• The weight of the vehicle also contributes to the amount of friction created - this is why one sees Drift Cars stripped to the bare minimum, so that there is less friction and the initiation of the drift is relatively easy. When braking, accelerating or cornering, the weight of the vehicle shifts from one set of wheels to another so that some tires may lose traction while others are still gripping the road adequately.
• Suspension alignment angles also affect a tire's traction. The tire gains most traction when its tread surface is flat on the road. Preloading a tire through adjustment of camber and toe angles is used to great effect in establishing and adjusting handling characteristics of a vehicle.
• Inflation pressures have a further effect. An under-inflated tire presents a larger surface to the road compared to one that is over-inflated. However, side-wall flex is greater in an under-inflated tire - which can be dangerous and also makes fuel consumption far worse.

Understanding the precise behavior of tires is a complex matter, the difference between dynamic and static friction of rubber is significant and the degree of flex in the side-walls of the tire plays a significant part in how it will perform in practice. The force required to make a tire lose grip is much greater than that required to keep the tire slipping once it's moving. Hence, if a vehicle is made to turn too tightly or at too great a speed, an initial small slippage can easily turn into a dangerous skid that is not easily controlled. Tire design has an influence on sound levels produced by a moving vehicle,^[1] which effects along with aerodynamic produced sound are much greater than engine noise at high speeds (e.g. greater than 45 miles per hour).

[edit] Treads and tire wear

The grooves or treads found in most tires are there to improve contact between the tire and the road in wet conditions. Without such grooves, the water on the surface of the road would be unable to escape out to the sides of the wheel as the tire presses down onto the road. This causes a thin layer of water to remain between the road and the tire, which causes a complete loss of friction with the road surface. This causes hydroplaning, obliterating traction required for braking, cornering and hard acceleration.^[2] The grooves in the tread provide an escape path for the water. Some tire manufacturers claim that their tread pattern is designed to actively pump water out from under the tire by the action of the tread flexing.

If the road is dry, tire treads actually reduce grip since they reduce the contact area between the rubber and the road. For this reason treadless or 'slick tires' are often used in motor racing when the track is known to be smooth and dry. If it should rain unexpectedly during the race these slick tires can cause a dangerous loss of grip - which is why they are seldom used on conventional road cars.

The contact patch of a tire can be increased, in some circumstances, by lowering the tire pressure. Lowering the tire pressure is a technique used for off-road vehicles in sandy, muddy, or snowy areas, and for drag racing. Decreasing the tire pressure causes the tire to sag so more of the tire is in contact with the surface, giving better traction. It also helps the tire grip small obstacles as the tire conforms more to the shape of the obstacle, and is in contact with the object in more places. However, this increases fuel consumption, tire wear, tire temperature, and raises the likelihood of damage to the wheel if a hard object is struck. Tires that are not designed for variable or lower pressure (such as tires for conventional cars) buckle on hard roads due to their stiffer sidewalls, raising the center of the tire off the surface and reducing, rather than increasing, road contact. The buckling also causes the treads to be squeezed together, reducing their effectiveness. Furthermore, the abnormal stress on an underinflated tire, combined with the resulting temperature increase, can cause the tire to explode while driving.

Another technique to improve traction is to use a softer rubber in the treads so that they mould themselves to the shape of the road surface, though this wears the tire more quickly than harder tires. Since the rubber is softer when warm, race pit crews may even keep tires in warmers to keep new tires at the optimum temperature until they are to be driven on. Soft compound rubber would also improve traction in street vehicles, but it is seldom used because these tires wear out too quickly for normal use.

The depth of the tread grooves is an important part of car safety but that depth gradually reduces due to wear throughout the lifetime of a tire. When the tread on the outer perimeter of the tire wears away, reducing the tread depth, the tire should be replaced. Many countries have laws regulating the minimum tread depth on road vehicles and most modern road tires have built-in tread wear indicators. These take the form of small blocks of rubber moulded into the bottoms of the grooves of the tread at intervals around the tire. When the tread has worn down until the tops of those blocks are level with the top of the tread - then the tire needs to be replaced. If these blocks are not present, a tire tread depth gauge should be used to measure the depth.

In most vehicles, either the front or rear tires will wear faster than the others. Having mismatched tread depths can alter the handling of the car in unacceptable ways - so it is generally advisable to swap the front and rear tires as they wear down to even out the wear patterns. This is called rotating the tires. If the vehicle's suspension is somewhat out of adjustment, it is also possible for the tires to wear more on one side than the other - so it may also be beneficial to rotate the tires from one side of the car to the other - however, careful attention should be paid to the owner's manual since some vehicles require particular tire rotation patterns. Notably, some tires are designed to provide best traction only when spinning in a clockwise or counter-clockwise direction. In such cases one must not rotate the tires from one side of the car to the other because that would put a 'clockwise tire' onto a wheel that turns in a counter-clockwise direction (and vice versa). Such tires typically have an arrow moulded into the sidewall to indicate the preferred direction.

[edit] Tire types

[edit] 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.

[edit] 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. Various types of solid tire have met with little success since the safety bicycle became widespread a hundred years ago. 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 aluminium 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 higher 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 edges 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.

Tires are checked at the point of manufacture for excessive static imbalance and dynamic imbalance using automatic Tire Balance Machines

With the introduction of radial tires 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 stiffness around the tire. These variations are collectively referred to as Tire Uniformity. Tire Unifomity is characterized by Radial Force Variation (RFV), Lateral Force Variation(LFV), and Tangential Force Variation. Radial and Lateral Force Variation is measured on a Force Variation Machine at the end of the manufacturing process. Tires outside the specified limits for RFV and LFV are rejected. In addition, Tire Unifrmity Machines are used to measure geometric parameters including Radial Runout, Lateral Runout, and Sidewall Bulge.

[edit] Automobile and truck tires

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.^{[citation needed]}

[edit] 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 tread surface area for dry weather performance. The ability to provide a high level of performance on both wet and dry pavement varies widely between manufacturers and even tire models of the same manufacturer. This is an area of active 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 meet the literal wording of the law, if not the intent, are available.
  • R compound tires, similar to cheater slicks, are considered 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. NOTE DOT does not "Approve" tires.
  • The highest performance tires 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 must be replaced with winter or all-season tires if the vehicle is to be driven much in the winter.

• Winter (snow and ice) tires
  • Winter tires are designed to provide improved performance under winter conditions compared with 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, thus providing better grip on ice and snow, but wearing more quickly at higher temperatures. Winter tires may have well above average numbers of the fine grooves 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, or the words MUD AND SNOW (but see All-season tires, below)
  • Some winter tires may be designed to accept the installation of metal studs for additional traction on icy roads. The studs also roughen the ice, 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 locales due to the increased road wear caused by studs. Typically, studs are never used on heavier vehicles. Studded tires are used in the upper tier classes of ice racing.
  • 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 is a compromise between one developed for use on dry and wet roads during summer and one developed for use under winter conditions. The type of rubber and the tread pattern best suited for use under summer conditions cannot, for technical reasons, give good performance on snow and ice. The all-season tire is a compromise, and is neither an excellent summer tire nor an excellent winter tire. They have, however, become almost ubiquitous as original and replacement equipment on automobiles marketed in the United States, due to their convenience and their adequate performance in most situations.
  • All-Season tires are also marked for mud and snow (e.g. M+####&S, etc.) the same as winter tires. Owing to the compromise with performance during summer, winter performance is usually poorer than a winter tire.
• Run flat tire
• All-terrain tire
  • All-terrain tires are typically used on SUVs and light trucks. These tires often have stiffer sidewalls for greater resistance against puncture when traveling off-road, the tread pattern offers wider spacing than all-season tires to remove mud from the tread.
  • 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. The large open design also allows mud to clear quickly from between the lugs.
  • Mud terrain tires also tend to be wider than other tires, to spread the weight of the vehicle over a greater contact patch to prevent the vehicle from sinking too deeply 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 contact area with the road which limits traction. The large lugs on mud tires tend to tear and chip on roads since 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, etc.) the same as winter tires.
• Sand tires
  • Tires for use in soft sand are very wide and run at low pressure. The shallow tread pattern is a series of polygonal blocks with angled shoulders. These are designed to press into the sand and gain support by increasing the friction between the grains. Conventional mud terrain tread patterns which rely on the shear strength of the ground merely cut into the sand and scoop it away, quickly digging the tire in.
  • Sand tires are ineffective in mud, where the low pressure and tread pattern does not bite into the ground.

[edit] Ratings

Tires are rated for a variety of purposes and standards. One rating given to tires which plays an important role is the Speed Rating. This is usually found in the form of a letter within the size code of the tire. For example, a tire with the code P205/55 R16 89H is "H" rated. This code refers to the maximum speed a tire can safely travel. Higher ratings generally correlate with better handling performance, all other things being equal.

The ratings are defined as follows:

Rating Code	Maximum speed (km/h)	Maximum speed (mph)
M	130	81
N	140	87
P	150	93
Q	160	99
R	170	106
S	180	112
T	190	118
U	200	124
H	210	130
V	240	149
Z	240+	149+
W	270	168
Y	300	186

Automobile tires have numerous rating systems. See tire code. These include ratings for traction, treadwear, and temperature resistance, sometimes known as UTQG ratings.

[edit] Aviation tires

Aviation tires on airplanes are designed to withstand heavy loads. On narrowbody aircraft, there are usually 6 tires, consisting of 2 wheels for each main landing gear and 2 front tires at the nose landing gear. Heavier aircraft, such as the Antonov An-124 and widebody aircraft such as the Boeing 747 the Airbus A340 and the Boeing 767 have a series of wheels, not a set. With more landing gears and bogies which carry more tires each, they also have tires spaced further apart than narrowbody aircraft. Widebody or heavy aircraft have a series of wheels because landing can impose a dynamic load as much as 100,000 pounds beyond rest weight. The plane needs to distribute the weight evenly and soften the load, making a smoother landing, saving costs on tires, putting less stress on the landing gear and on the runway. Planes with a series of landing gears often have a stop bar in front of the first row of wheels to act as brakes. On a plane with 4 tires per main landing gear they are usually mounted on a rack type boggie, which keeps the landing gear in a diagonal almost vertical, attitude. When the plane touches tarmac, the last(second) row of the main landing gear touches the ground first thus forcing the 1st row of tires down. Multi wheeled landing gears or planes have more wheels to reduce the amount of shock transferred to the fuselage thus making a more comfortable landing.

These are filled with nitrogen gas, to remain inert at the various pressures the aircraft will undergo in a flight.

Aviation tire treads only have lateral traction strips, since the plane doesn't have power sent through their wheels. The tires have deep siping because it helps the plane maintain an extremely high amount of grip during crosswind landings. The wide siping also prevent hydroplaning off the runway. Aviation tires are expensive, costing up to $4,000 a tire (Goodyear on-line price list). Aviation tires generally operate at high pressures, up to 200 psi for airliners and higher for business jets. If aviation tires are not deflated before disassembly serious injury or death can result. Proper inflation is of the utmost importance as under-inflation can result in tire damage, aircraft damage or loss of the aircraft. (see the video "Death of an Airline" Maintenance and Ramp Safety Society, c1998)

Aviation tires also include heat fuses, which melt when a certain temperature is reached. Tires often overheat if maximum braking is applied during a rejected takeoff or an emergency landing. The fuses provide a safer failure mode, since the tire will no longer explode when overheated, but deflate in a controlled way, thus minimizing damage to aircraft or injury to people on the ground. (especially firefighters or passengers and crew during an evacuation)

[edit] Railway tires

The steel wheels of steam locomotives are usually fitted with steel tires to provide a replaceable wearing element on a costly wheel.

(Some trains, mostly rubber-tyred metros and people movers, have rubber tires, including some lines of the Paris Métro, the Mexico City Metro, the Caracas Metro, the Montreal Metro, Sapporo Subway, and the Santiago Metro).

A different form of damage to railroad wheels takes place if violent wheel slip occurs. The friction caused can heat the wheel (and rail) enough to cause heat damage.

Replacing a whole wheel because of a worn contact surface is expensive, so steam locomotive driving wheels are fitted with replaceable steel tires. The tire is a hoop of steel that is fitted around the steel wheel. No obvious fastening is generally used to attach it. As with wagon wheels, the tire is held in place by an interference fit - it is made slightly smaller than the wheel on which it is mounted. To install a tire it is heated 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 onto the wheel. After placing it on the wheel, the tire is cooled, and it shrinks onto the wheel. When cold, friction between the tire and the wheel is such that the tire will not budge, even under 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 material remaining, it can be turned on a wheel lathe to refinish it, reshaping it to the correct profile.

[edit] Maintenance and safety 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 worn out and should be replaced. The same wheels can usually be used throughout the lifetime of the car. Uneven or accelerated tire wear can be caused by under-inflation, overload or bad wheel alignment. Greater 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, especially when the wear on the outer rubber exposes the reinforcing threads within, the tire is said to be bald and 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. Since this bonding may occasionally come loose, new tires are considered superior to recapped ones.

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 safely. A leak may be a slow one, such as when the seal between the rim and tire edge is not perfect. Many leaks in flat tires are caused by nails, screws, caltrops, broken glass or other sharp objects puncturing the tire. 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 located by submerging the pressurized tire in water to see where air bubbles emerge. If submerging a tire underwater is not possible, the leak can be searched for by covering the pressurized tire surface with a soap and water 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, then the protruding ends of the plug can be cut off, and the tire can be refilled with air to the appropriate pressure, and the repaired wheel reinstalled on the vehicle. Patches covering a hole can be glued or rubber-cemented to the interior surface of a tire, 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.

It should be noted that a plug-only or patch-only type repair is not an acceptable repair. Ref.

Sometimes a more serious rupture of the tire material occurs resulting in a blowout. A "blowout" may also be caused by running at highway speeds while the tire is significantly under-inflated. The heat generated can melt the body cord and an explosive loss of air may occur if the driver continues to operate the vehicle. A tire thus damaged usually must be replaced. 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 the event of flat tire or blowout. Many spare tires (sometimes called "doughnuts") for modern cars are smaller than normal tires (to save on trunk space, gas mileage, weight and cost) and should not be driven very far before replacement with a full-size tire. A few modern vehicle models may use conventional spare tires. Jacks and for emergency replacement of a flat tire with a spare tire are included with 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.

Some modern cars and trucks are equipped with run flat tires that may be driven with a puncture over a distance of 80 km to 100 km. This eliminates the need for an immediate stop, and the associated expensive tow service or tire change.

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 facilitate uniform 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. This measurement of tire inflation pressure should be made at least once a month. The properinflation pressure is located in the owner's manual and on the Tire Placard. Because of slow leaks or changes in weather or other conditions tire pressure may occasionally have to be corrected, usually via the valve stem with compressed air which is often available at service stations.

Some modern cars now incorporate automatic tire pressure sensing with a warning light indicating when tires have become dangerously deflated. These systems use the measurements from the wheel speed sensors at each wheel. Since a partially deflated tire has a slightly smaller diameter than a correctly inflated tire, the car ABS computer can check that all four wheels make approximately the same number of rotations when averaged over many miles of driving. If one wheel consistently makes more rotations than the others then it must be deflated, and the warning light is lit. However, vehicle operators should not wait for the low pressure warning light to illuminate before they check their tire pressures. In most cars the tire pressure sensing must be reset (typically by holding down a button) whenever the tire pressure is corrected.

Tires may gradually lose pressure in all four wheels simultaneously, a situation that the ABS pressure sensing system cannot detect. Because of this the ABS TPMS was rejected in the final ruling of the United States TREAD Act. As from September 2007 all cars and light vehicles must have a direct tire pressure monitoring system. These are currently, 2006, battery powered sensors in the wheel transmitting to a dashboard mounted display.

There are hopes that a batteryless system will be marketed by Lear in 2007 for fitting to new cars. This will avoid having a large number of lithium batteries to dispose of. It is likely the European Union will introduce similar legislation by 2010 when the lessons of the US legislation will be apparent.

See also: Run flat tire  and Tire IQ

[edit] Tire manufacturing

Main article: Tire manufacturing

[edit] Notable tire manufacturing companies

• Apollo Tyres[3]
• Avon Tyres
• Bridgestone[4]
• Continental
• Barum
• Carlisle
• Cheng-shin/MAXXIS
• Cooper
• Dunlop
• Eurotire[5]
• Falken Tire
• Firestone
• GITI TIRE[6]
• B.F. Goodrich
• Goodyear
• Hankook Tire
• JKtyre[7]
• Kelly Springfield Tire and Rubber Company
• Kenda
• Kumho
• Michelin
• Uniroyal
• Metzeler
• MRF Tyres[8]
• Nokian Tyres
• Pirelli
• Sumitomo Rubber Industries
• Toyo
• Yokohama

[edit] Other use and recycling

Used tires with unsafe amounts of wear 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 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 be extinguished, creating large volumes of toxic air pollution,^[3] oil, and heavy metals. Some such fires have become Superfund cleanup sites. In addition, a tire carcass accumulates water from rain, making tire dumps breeding grounds for mosquitos.

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 reused in other products; it also yields much energy when burned under controlled conditions.

Retreadded or recapped tires were once common, the rubber tread of a tire would wear long before the remainder of the carcass. Therefore good carcasses were simply overlaid with another tread and returned to service. Because this bonding may occasionally come loose from the tire, new tires were superior to retreaded tires. With advances in tire technology leading to longer tread life and the changes in the economics of raw materials and labor, this is no longer economically advantageous for car tires. However many manufacturers are making heavy truck tires which they claim can be re-treaded up to four times. The cost to the haulier is approximately a third the cost of a new tire. From the point of view of the manufacturer the tire uses half the oil and the carcase is re-used so it is proftable to both parties.

While salvaged tires make cheap toys which can be used variously for pets, animals in captivity or children, e.g. the once 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 has significantly increased its tire reclamation efforts to slightly more than 80 percent. In 2003, tire reclamation statistics were:

• 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 life as retreads.

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

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 bonded, for use as walkways, edging, tree rings, or stepping stones. Both types of product are also marketed as excellent injury-preventing (shock absorbing) surfacing material for playgrounds, being longer lasting and more resilient that the usual materials used, e.g. sand, gravel, or shredded wood or bark. Although the materials are extremely resistant to breakdown and essentially last forever, the possibility of toxic agents, especially heavy metals, leaching out and contaminating the soil, particularly where food crops are grown, is currently under investigation.

Individuals have used old tires as planters. They are particularly popular with individuals growing tomatos or other plants which prefer warm temperatures, as the black color absorbs the infrared from the sun. [9], [10], [11], [12], [13], [14]

Inner tubes can be cut into loops and used as heavy duty rubber bands, sometimes known as snoopy loops.

[edit] See also

All-terrain tire Beadlock Cold inflation pressure DUKW - a vehicle that allows the driver to inflate and deflate the tires from inside the cab. Landfill liner Mud-terrain tire Retread Run flat tire Tire Pressure Monitoring System (TPMS). Tweel, a newly developed non-pneumatic tire. Slick tire Tire load sensitivity Non-pneumatic tire Tire code Tire Recycling Tire rotation Wheel alignment Whitewall tire

Automotive Handling: Car handling Center of mass Drifting Electronic Stability Control Fishtailing Inboard brake Oversteer Steering Suspension (vehicle) Tire Understeer Unsprung weight Vehicle dynamics Weight transfer

[edit] References

[edit] External links

1911 Britannica article Car Bibles : The Wheel and Tyre Bible A good independent technical resource Tire / Wheel Size Calculator