TIRE, TYRE, TIRES, TYRES

A tire or tyre (see spelling differences and etymological origins) 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, but other materials such as steel may be used.

History

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 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Dunlop re-invented the tire for his ten year old son's tricycle in 1887 and was awarded a patent for his tire in 1888 (rescinded 1890).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 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 Compact Oxford English Dictionary, the word might originate from a shortening of attire, due to it being the wheel clothing. 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 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.
Some air-filled tires, especially those used with spoked 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 tire). 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.

Tire Physics

How a tire is composed changes the coefficient of friction of a tire, although other factors are also taken into effect, such as the type of surface that the rubber tire is on, and the conditions of the road. In terms of grip, a bald tire has excellent grip on dry pavement, while the same tire on the same pavement but in wet conditions has poor grip. This can go both ways- a patterned tire has grooves in which water can be squeezed into, therefore giving more surface area, and more traction, however in dry conditions its traction is not as good compared to a bald tire, as the grooves on its surface decrease the surface area, and therefore the coefficient of friction. According to Physics 101; "A patterned tire gives typical dry and wet frictional coefficients of about 0.7 and 0.4, respectively." Also, the weight of the car also contributes to the amount of friction created-this is why one sees Drift Cars stripped to the bare minimum, so that the initiation of the drift is relatively easy. This is due to the formula:
Force of Friction=Coefficient of Friction * Normal Force
where Normal Force is the opposite and equal reaction to the force of gravity (mass*9.81 ms-2) on the car. The heavier the car, the higher the normal force, and the higher the force of friction created.
Additionally, the angle in which a tire hits the ground also contributes to the traction. Wheels are given an outward tilt, most commonly less than a degree, so that when the vehicle becomes loaded, the wheels are nearly vertical (Mc Graw Hill, 1984). This allows the tires to become as close to parallel as possible to the road, allowing for maximum traction.

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's surface, which causes a severe loss of grip. At higher speeds, this can cause hydroplaning, substantially reducing traction during braking, cornering and hard acceleration. The grooves in the tread provide an escape path for the water - and it is even claimed by some tire manufacturers 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. 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; decreasing tire pressure also increases road contact,[citation needed] but decreases energy efficiency and increases the risk of hydroplaning. Since the rubber is softer when warm, race pit crews may even keep tires in a freezer 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.

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 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.
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 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. See tire code. 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

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 pressure sensing system cannot detect. Road holding and fuel economy may be compromised by a smaller loss of pressure than the sensor is able to detect. An alternate system directly measures the inflation pressure of the tire.

Run flat tires

A run flat tire is a pneumatic vehicle tire that is designed to resist the effects of deflation and to enable the vehicle to continue to be driven — albeit at reduced speeds (i.e. 80 km/h or 50 mph) and for limited distances (80 km or 50 mi).
All of the major tire manufacturers offer a run flat tire of some kind.
The tire is built with stiffer side-walls that can bear the weight of the vehicle even when the pressure within the tire is greatly reduced. The side-walls are typically constructed of layers of rubber and a heat-resistant cord that prevent the side-walls from folding or creasing. The bead around the edge of the tire is also specialised to grip the wheel rim such as to avoid becoming detached from the rim.
Self-supporting run flat tires are fairly common on light trucks and passenger cars and typically provide for the vehicle to drive for 50 miles at around 50 miles per hour. However, if the tires are treated to this kind of punishment, they may still be irreparably damaged in the process.
There are also issues with repairing punctures in run-flat tires if the puncture is in the side wall or near the edge of the tread.
The first vehicle ever to be sold with run-flat tires was the Mini 1275GT in July 1974. It used the Dunlop Denovo system which required special wheels and featured ultra-low profile side-walls.