Tire

Firestone tire

A tire (US spelling) or tyre (UK spelling) is a roughly toroidal piece of (usually) rubber placed on a wheel to cushion it. 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.

Air-filled tires are known as pneumatic tires, and these are the type in almost universal use today. 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.

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 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, tend 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.

Some tire manufacturing companies include:

• Bridgestone
• Continental
• Cooper
• Dunlop
• Firestone
• Goodyear
• Michelin
• Pirelli
• Toyo tires

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 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 the resistance to damage. 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] (http://www.cartalk.com/content/columns/Archive/1994/November/11.html)

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 (http://www.mearns.org.uk/stonehaven/thomson.htm)

Automobile tires

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 165mm wide tires, while the rear tires of the 2000 Dodge Viper fit 335mm 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 100mm 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 traction, treadwear, and speed 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 at least 1/8". 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.
• 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 perform 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 then a all-season tire 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.

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.

Train tires

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

(Some trains, mostly Metros, have rubber tires, including some lines of the Paris Métro, and the Montreal Metro).

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. Instead, 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 until it is 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, 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.

See also

• Used tires and Waste
• Philip Strauss, treasurer of the Hardman Tyre & Rubber Company, applied an invention of his father's (Alexander Strauss) to produce a combination fabric reinforced hardened rubber tire and rubber inner tube. Patented in 1911.
• rolling friction
• Slick tyre
• All-terrain tyre
• Mud-terrain tyre
• Whitewall tire
• Tweel, a similar technology to the one listed above but created by the Michelin corporation and a different design.
• DUKW "The DUKW was the first vehicle which allowed the driver to inflate and deflate the tires from inside the cab, fully inflated for hard surfaces like roads and less inflated for softer surfaces - especially beach sand."

External links

• The Tire Society (http://www.tiresociety.org/)
• DMOZ open directory (http://dmoz.org/Shopping/Vehicles/Parts_and_Accessories/Wheels_and_Tires/)
• Rubber Manufacturers Association tire composition (http://www.rma.org/scrap_tires/scrap_tire_markets/scrap_tire_characteristics/)

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