Tire

Firestone tire

A tire (U.S. spelling) or tyre (UK spelling) is a roughly toroidal piece of material placed on the circumference of a wheel, either for the purpose of cushioning or to protect the wheel from wear and tear.

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 Schrader valve. Attempts have been made to make various types of solid tire but none has so far met with much success. The "steering feel" of such tires is 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.

A common motor vehicle tire is mounted around a steel rim 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 rim with the tire mounted onto it comprises the removable wheel, which is then attached to the vehicle through a number of holes in the rim 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. The same device used to mount a tire onto a rim is also used to remove a tire from the rim, again when the wheel is off the vehicle. On the wheels of many vehicles, hubcaps are often snapped in place over the part of the rim facing outside and the tightened lug nuts for decoration and, to some extent, for protection from the elements to reduce rusting of the rim and lug nuts. Some rims are already decoratively made and plated with chrome, so hubcaps are not used over them. The hubcap must be removed to take off the tire, and after the tire is replaced, the hubcap is put back on.

The outer perimeter of the tire, often called the crown, has various designs of jagged shaped grooves in it. 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 tire to road contact. Without such grooves, a layer or film of water would form between the wet roads and the tire surface, which would substantially reduce the traction making the tire contact with the road very slippery. 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 tire inevitably wears away from use, 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.

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 (for example Kenyan 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.

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 vulcanized rubber, the material that would later be used to produce tires.

John Boyd Dunlop, a veterinary surgeon living in Belfast Ireland, is widely 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 Scottish engineer Robert William Thomson 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.

Carbon black was added to tires to improve durability and provide damage resistance, particularly from ultraviolet light from the sun. In recent years less of it is being used in order to improve gas mileage, and the resulting reduction in electrical conductivity makes static electricity more likely to build up and arc between a person and the metal part of the door when getting out of a car. [1]

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.

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's company has since merged with the Goodyear 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 belts 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.

External link: Robert William Thomson

Etymology

The word is a corruption of attire.

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 contract and imparting stiffness to the wheel. This work was done by a wheelwright, a craftsman who specialized in making wagon wheels.

Maintenance

Friction from moving contact with the road causing 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 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 often caused by driving over nails, screws, 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. This often rather simple kind of tire repair can typically be done without having to take the tire off the rim, so many car owners can do it themselves with a tire repair kit made for this purpose. 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 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.

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.

Automobile tires

Formula One tires being pushed on to the grid in carts at the 2005 United States Grand Prix

Automobile tires have numerous rating systems. The size of a tire is measured with a single code, in the form AAA/BBRCC for radial tires. This code is often a source of confusion, as its format is an obscure mix of inches, millimeters, and percentages.

In this form, AAA is the width of the tire, measured in millimeters. 200 is a common figure, but the range can be quite wide. The 2000 Honda Insight uses 165 mm wide tires, while the rear tires of the 2000 Dodge Viper fit 335 mm tires.

BB is the "profile", i.e. the height of the sidewall (the distance from the edge of the wheel to the edge of the tire), measured as a percentage of AAA, the tire width. A 200/50 tire would have a 100 mm high sidewall. If the number BB is missing (e.g. 145/R12) then the height is 80% of the width.

CC is the diameter of the wheel the tire is designed to fit on in inches. With of all three of these numbers you can calculate the total diameter of the tire.

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. 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 end up in the food chain.

Types of automobile tires

Performance 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.
- Performance tires are often called summer tires, because they sacrifice wet weather handling, by having shallower water channels, and tire life from softer rubber compounds, for dry weather performance. The ultimate variant of perfomance tires has no tread pattern at all and is called slick tire.
Winter tires
- Winter tires are designed to remain pliable in subzero temperatures. They often have fine grooves and siping in the tread patterns that are designed to bite into the ice and snow on the road. 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.
- Many winter tires are designed to be studded for additional traction on icy roads.
All-season tires
- Most automobile tires are all season tires. These tires are an attempt to satisfy the needs of most road conditions, they have the deeper water channels that are found in winter tires, but often have harder rubber compound for greater tire life in warm weather.
- All-season tires attempt to strike a balance between performance, wet weather and comfort.
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.

Train 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.

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

Efficient though the rolling of steel wheel on 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.