Firestone tire

Tires or tyres (in American and British English, respectively) are pneumatic enclosures used to protect and enhance the effect of wheels.

Tires are used on many types of vehicles, from bicycles to cars to earthmovers to aircraft. Tires enable vehicle performance by providing for traction, braking, steering, and load support. Tires are inflated with air, which provides a flexible cushion between the vehicle and the road that smoothes out shock and provides for a comfortable ride.

History

The earliest tires were bands of iron (later steel), placed on wooden wheels, used on carts and wagons. The tire would be heated in a forge fire, placed over the wheel and quenched, causing the metal to contract and fit tightly on the wheel. A skilled craftsman, known as a wheelwright, did this work. The tension of the metal band served the purpose of holding or "tying" the wooden spokes of the wheel together, hence the term "tire." In addition to tying the spokes together, the tire also provided a wear-resistant surface to the perimeter of the wheel. As wheels changed over time, the term "tire" continued to be used for the outer band even when it no longer served the purpose of tying the spokes together.

The first practical pneumatic tire was made by the Scot John Boyd Dunlop for his son's bicycle, in an effort to prevent the headaches his son had while riding on rough roads (Dunlop's patent was later declared invalid because of prior art by fellow Scot Robert William Thomson). The pneumatic tire also has the more important effect of vastly reducing rolling resistance compared to a solid tire. Because the internal air pressure acts in all directions, a pneumatic tire is able to "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction of travel, as is the case with a solid (or foam-filled) tire. The difference between the rolling resistance of a pneumatic and solid tire is easily felt when propelling wheelchairs or baby buggies fitted with either type so long as the terrain has a significant roughness in relation to the wheel diameter.

Pneumatic tires are made of a flexible elastomer material such as rubber with reinforcing materials such as fabric and wire. Tire companies were first started in the early 20th century, and grew in tandem with the auto industry. Today over 1 billion tires are produced annually, in over 400 tire factories, with the three top tire makers commanding a 60% global market share.

Chronology

• 1843 – Charles Goodyear announces vulcanization
• 1846 – Robert William Thomson invented and patented the pneumatic tire
• 1870 – BFGoodrich founded
• 1871 – Continental AG founded
• 1888 – First commercial pneumatic bicycle tire produced by Dunlop
• 1888 – Michelin Tire Company founded
• 1889 – Dunlop Tire Company founded
• 1889 – John Boyd Dunlop patented the pneumatic tire in the UK
• 1890 – Dunlop and William Harvey Du Cros began production of pneumatic tires in Ireland
• 1890 – Bartlett Clincher rim introduced
• 1891 – Dunlop's patent invalidated in favor of Thomson’s patent
• 1892 – Beaded edge tires introduced in the U.S.
• 1894 - E.J. Pennington invents the first balloon tire
• 1895 – Michelin introduced pneumatic automobile tires
• 1898 – Schrader valve stem patented
• 1898 – Goodyear Tire and Rubber Company founded
• 1900 – Firestone Tire & Rubber founded
• 1900 – Cord Tires introduced by Palmer (England) and BFGoodrich (U.S.)
• 1903 – Goodyear Tire Company patented the first tubeless tire, however it was not introduced until 1954
• 1904 – Goodyear and Firestone started producing cord reinforced tires
• 1904 – Mountable rims were introduced that allowed drivers to fix their own flats
• 1906 – First pneumatic aircraft tire
• 1908 – Frank Seiberling invented grooved tires with improved road traction

• 1910 – BFGoodrich Company invented longer life tires by adding carbon to the rubber
• 1917 – Yokohama Rubber Company founded
• 1919 – Goodyear and Dunlop announced pneumatic truck tires^[1]
• 1931 - Bridgestone Tire Co. Ltd. founded by Shojiro Ishibashi (Ishibashi means "stone bridge")
• 1938 – Goodyear introduced the rayon cord tire
• 1940 – BFGoodrich introduced the first commercial synthetic rubber tire
• 1946 – Michelin introduced the radial tire
• 1947 – Goodyear introduced first nylon tires
• 1947 – BFGoodrich introduced the tubeless tire
• 1963 – Use of polyester cord introduced by Goodyear
• 1965 – Armstrong Rubber introduced the bias belted fiberglass tire
• 1965 – BFGoodrich offered the first radial available in North America
• 1967 – Poly/glass tires introduced by Firestone and Goodyear
• 1968 – United States Department of Transportation (DOT) numbers required on new tires in USA
• 1974 - Pirelli introduced the wide radial tire, wich is the international standard in tires today
• 1986 – BF Goodrich merged with Uniroyal to form Uniroyal-Goodrich
• 1987 – General Tire acquired by Continental
• 1988 – Firestone acquired by Bridgestone
• 1988 – Uniroyal-Goodrich acquired by Michelin
• 1999 – Goodyear acquired certain Dunlop tire factories from Sumitomo Rubber Industries
• 2005 – Pneuhage and Continental introduced first factory for tire services (aftermarket (automotive))
• 2006 – Bridgestone acquired Bandag (retread maker)

For a list of tire companies and the dates they were established, see List of Tire Companies.

Terms

Tread

The tread is that portion of the tire that comes in contact with the road. The tread is a thick rubber compound formulated to provide a high level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, lugs, and voids. Grooves run circumferentially around the tire, and are needed to channel away water. Lugs are that portion of the tread design that contacts the road surface. Voids are spaces between lugs that allow the lugs to flex. Tread patterns feature non-symmetrical lug sizes circumferentially in order to minimize noise.

Treads are often designed to meet specific product marketing positions. High performance tires have small void ratios to provide more rubber in contact with the road for higher traction, but may be compounded with softer rubber that provides better traction, but wears quickly. Mud and snow tires are designed with higher void ratios to channel away rain and mud, while providing better gripping performance. When installing new tires, you should try and replace all four at once. Installing just two new tires on the front or rear will encourage under steer or over steer, depending on the vehicle and position of the new tires.

Snow tires are a very special kind of tire. They actually gain traction when it is cold, whereas, other tires lose traction on the ice and snowy roads.

Tread lug

Tread lugs provide the contact surface necessary to provide traction. As the tread lug enters the road contact area, or footprint, it is compressed. As it rotates through the footprint it is deformed circumferentially. As it exits the footprint, it recovers to its original shape. During the deformation and recovery cycle the tire exerts variable forces into the vehicle. These forces are described as Force Variation.

Tread void

Tread voids provide space for the lug to flex and deform as it enters and exits the footprint. Voids also provide channels for rainwater to flow out of the footprint. Voids also provide space for mud and snow to be channeled away from the footprint. The void ratio is the void area of the tire divided by the entire tread area. Low void areas have high contact area and therefore higher traction.

Rain groove

The rain groove is a design element of the tread pattern specifically arranged to channel water away from the footprint. Rain grooves are circumferential in most truck tires. Many high performance passenger tires feature rain grooves that are angled from the center toward the sides of the tire. 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. This results in a smoother ride in different types of weather.

Sipe

Tread lugs often feature small narrow voids, or sipes, that improve the flexibility of the lug to deform as it traverses the footprint area. This reduces shear stress in the lug and reduces heat build up. Sipes also provide greater traction in icy conditions.

Wear bar

Wear bars are raised features located at the bottom of the tread grooves that indicate excessive tire wear. When the tread lugs are worn to the point that the wear bars connect across the lugs, the tires are fully worn and should be taken out of service.

Contact patch

Main article: contact patch

The contact patch, or footprint, of the tire is the area of the tread in contact with the road. This is the area that transmits forces between the tire and the road via friction. The length-to-width ratio of the contact patch will affect steering and cornering behavior.

Bead

The bead is that part of the tire that contacts the wheel. The bead is reinforced with steel wire, and compounded from high strength, low flexibility rubber. The bead seats against the wheel tightly to ensure that the tire holds air without leakage. The bead fit is tight also to ensure the tire does not shift circumferentially as the tire rotates.

Sidewall

The sidewall is that part of the tire that bridges between the tread and bead. The sidewall is reinforced with rubber and fabric plies that provide for strength and flexibility. The sidewall transmits the torque applied by the drive axle to the tread in order to create traction. Sidewalls are molded with decorative ornamentation, government mandated warning labels, and other consumer information.

Over time, rubber degrades. Ford has recommended that tires be replaced when they are 6 years old to prevent sudden failure, even if the tire looks undamaged. In tropical climates, such as in Singapore, tires degrade sooner than in temperate climates.

Shoulder

The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.

Inner tube

Bicycle tires and some passenger and truck tires are designed for use with inner tubes. Inner tubes are torus shaped balloons made from a material impervious to air leakage. The inner tubes are inserted into the tire and inflated to give the tire its final shape.

Wheel

Tires are mounted to wheels, or rims, that bolt to the drive axle. Automotive wheels are either made from cast metal alloys, or stamped/welded metal. According to The Merriam's Webster Dictionary the rim is the outer part of the wheel, the tire does mount to the rim but a rim is not a wheel

Valve stem

The valve stem is a tubular rubber shape with a metal valve used to inflate the tire with air. Valve stems usually protrude through the wheel for easy access for inflation. Tires are inflated through a valve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve on high performance bicycles. The rubber in valve stems eventually degrades. Replacement on the valve stem at regular intervals reduces the chance of failure.

Tire pressure monitoring system

Main article: Tire pressure monitoring system

Tire pressure monitoring systems are electronic systems that continuously monitor tire pressure on a vehicle, and alarm when the pressure goes below a warning limit. There are several types of designs to monitor tire pressure. Some actually measure the air pressure and some make indirect measurements, such as gauging when the relative size of the tire changes due to lower air pressure. These systems are becoming mandatory in countries such as the United States.

Load rating

Tires are specified by the manufacturer with a maximum load rating. Loads exceeding the rating can result in unsafe conditions that can lead to steering instability and even rupture. For a table of load ratings, see tire codes.

Inflation pressure

Tires are specified by the manufacturer with a recommended inflation pressure that permits safe operation within the specified load rating. Most tires are stamped with a maximum pressure rating. For passenger vehicles and light trucks, the tires should be inflated to what the vehicle manufacturer specifies, which is usually located on a decal just inside the driver's door.

Speed rating

The speed rating denotes the maximum speed at which a tire is designed to be driven for extended periods of time. The ratings range from 99 mph (160 km/h) to 186 mph (300 km/h). For a table of speed ratings, see tire code.

Rotation

Tires do often exhibit irregular wear patterns once installed on a vehicle and partially worn. Tire rotation is the procedure of moving tires to different car positions, such as front-to-rear, in order to even out the wear, thereby extending the life of the tire.

Wheel alignment

Main article: Wheel alignment

Once mounted on the vehicle, the tire may not be perfectly aligned to the direction of travel, and therefore exhibit irregular wear, often quite substantial. A wheel alignment is the procedure for checking and correcting this condition through adjustment of camber, caster and toe angles. These settings also affect the handling characteristics of the vehicle.

Retread

Main article: retread

Tires that are fully worn can be re-manufactured to replace the worn tread. Retreading is the process of buffing away the worn tread and applying a new tread. Retreading is economical for truck tires because the cost of the replacement is small compared to the cost of the tire carcass. Retreading is less economical for passenger tires because the cost is high compared to the cost of a new tire.

Flat

Main article: Flat tire

A flat tire occurs when the tire deflates to the point that the metal of the wheel comes to ground level. This can occur as a result of a wear-and-tear, a leak, or more serious damage. A flat tire seriously impairs the ability of the vehicle to be driven, requiring the vehicle to be safely removed from the road, and the tire to be changed. Continuing to drive a vehicle with a flat tire may result in damage to the tire or the vehicle, and may put the occupants and other vehicles in danger.

Hydroplaning (or aquaplaning)

Main article: Hydroplaning (road vehicle)

Hydroplaning, also known as aquaplaning, is the condition where a layer of water is present between the tire and road. Hydroplaning occurs when the tread pattern cannot channel away water at an adequate speed to ensure a complete dry footprint area. When hydroplaning occurs the tire loses traction and steering, and creates a very unsafe driving condition. When hydroplaning occurs, there is less responsiveness of the steering wheel. The correction of this unsafe condition is to gradually reduce speed.

Markings

DOT Code

The DOT Code is an alphanumeric character sequence molded into the sidewall of the tire for purposes of tire identification. The DOT Code is mandated by the US Department of Transportation. The DOT Code is useful in identifying tires in a product recall.

The DOT Code begins with the letters "DOT" followed by a two numbers or letters plant code that identifies where it was manufactured. The last four numbers represent the week and year the tire was built. A three-digit code was used for tires manufactured before the year 2000. For example, 178 means it was manufactured in the 17th week of 8th year of the decade. In this case it means 1988. For tires manufactured in the 1990s, the same code holds true, but there is a little triangle (Δ) after the DOT code. Thus, a tire manufactured in the 17th week of 1998 would have the code 178Δ. After 2000, the code was switched to a 4-digit code. Same rules apply, so for example, 3003 means the tire was manufactured in the 30th week of 2003.

Other numbers are marketing codes used at the manufacturer's discretion.

E-mark

All tires sold in Europe after July 1997 must carry an E-mark. The mark itself is either an upper or lower case "E" followed by a number in a circle or rectangle, followed by a further number. An "E" (upper case) indicates that the tire is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. An "e" (lower case) indicates that the tire is certified to comply with the dimensional, performance and marking requirements of Directive 92/33/EEC. The number in the circle or rectangle denotes the country code of the government that granted the type approval. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tire size and type.

Mold serial number

Tire manufacturers usually embed a mold serial number into the sidewall area of the mold, so that the tire, once molded, can be traced back to the mold of original manufacture.

Codes

Main article: Tire code

Use classifications

Tires are classified into several standard types based on the type of vehicle they serve. Since the manufacturing process, raw materials, and equipment vary according to the tire type it is common for tire factories to specialize in one or more tire types. In most markets factories that manufacture passenger and light truck radial tires are separate and distinct from those that make aircraft or OTR tires.

Passenger and light truck types

High Performance

High performance tires are designed for use at higher speeds. They feature a softer rubber compound for improved traction, especially on high speed cornering. The trade off of this softer rubber is lower tread life.

High 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 among manufacturers, and even among tire models of the same manufacturer. This is an area of active research and development, as well as marketing.

Mud and Snow

Mud and Snow, or M+S, is a classification for winter tires designed to provide improved performance under winter conditions compared to tires made for use in summer. The tread compound is usually softer than that used in tires for summer conditions, thus providing better grip on ice and snow, but wears more quickly at higher temperatures. Tires may have well above average numbers of sipes in the tread pattern to grip the ice.

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).

Studded Tire

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, thus 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 that 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.

Mud tires are specialty tires with 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 area to prevent the vehicle from sinking too deeply into the mud. However in reasonable amounts of snow, snow tires should be thinner. Due to them having a thinner wheel base, the tire will have more pressure per square inch on the road, thus giving them greater traction. This does not compensate when the snow is too deep and the car can not move in the first place. In these circumstances a larger robust vehicle would be more adequate to get out of the snow drift.

All Season

The All Season tire classification 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 the same as winter tires. Owing to the compromise with performance during summer, winter performance is usually poorer than a winter tire.

All-terrain

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. Many tires in the all-terrain category are designed primarily for on-road use, particularly all-terrain tires that are originally sold with the vehicle.

Spare

Main article: spare tire

Some vehicles carry a spare tire, already mounted on a rim, to be used in the event of flat tire or blowout. Minispare tires are smaller than normal tires to save on trunk space, gas mileage, weight and cost. Minispares have a short life expectancy, and low speed rating.

Run-flat

Main article: run flat tire

Several innovative designs have been introduced that permit tires to run safely with no air for a limited range at a limited speed. These tires feature still load supporting sidewalls and often plastic load-bearing inserts.

Heavy duty truck

Heavy duty tires are also referred to as Truck/Bus tires. These are the tire sizes used on vehicles such as commercial freight trucks, dump trucks, and passenger busses. Truck tires are sub-categorized into specialties according to vehicle position such as steering, drive axle, and trailer. Each type is designed with the reinforcements, material compounds, and tread patterns that best optimize the tire performance.

Off-the-road (OTR)

The OTR tire classification includes tires for construction vehicles such as backhoes, graders, trenchers, and the like; as well as large mining trucks. These tires are built with a large number of reinforcing plies to withstand severe service conditions and high loads. OTR tires are used in rather low speed conditions.

Agricultural

The agricultural tire classification includes tires used on farm vehicles, typically tractors and specialty vehicles like harvesters. High flotation tires are used in swampy environments and feature large footprints at low inflation pressures.

Racing

NASCAR tires

Racing tires are highly specialized according to vehicle and race track conditions. This classification includes tires for top fuel dragsters, oval track racers, jet-powered trucks, and monster trucks, as well as the large-market race tires for Formula One and NASCAR. Tires are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Tires have also been specially engineered for drifting. Racing tires are often engineered to minimum weight targets, so tires for a 500 mile race may run only 300 miles before a tire change. Some tire makers invest heavily in race tire development as part of the company's marketing strategy and a means of advertising.

Industrial

The Industrial tire classification includes pneumatic and non-pneumatic tires for specialty industrial vehicles such as skid loaders and fork lift trucks.

Bicycle

This classification includes all forms of bicycle tires, including racing tires, mountain-bike tires, and snow tires.

Aircraft

Aircraft tires are designed to withstand heavy loads for short durations. The number of tires required for aircraft increases with the weight of the plane. Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking traction. Aircraft tires are usually inflated with nitrogen in order to minimize expansion and contraction from extreme changes in temperature experienced during flight. Dry nitrogen expands at the same rate as other dry atmospheric gases, but common compressed air sources may contain moisture, which increases the expansion rate with temperature. Aircraft tires generally operate at high pressures, up to 200 psi (13.8 bar) for airliners and even higher for business jets.

Aircraft tires also include heat fuses, designed to melt at a certain temperature. Tires often overheat if maximum braking is applied during a rejected takeoff or an emergency landing. The fuses provide a safer failure mode that prevents tire explosions by deflating in a controlled manner, thus minimizing damage to aircraft and objects in the surrounding environment.

The main purpose of requiring that an inert gas, such as nitrogen, be used instead of air, for inflation of tires on certain transport category airplanes is prompted by at least three cases in which the oxygen in air-filled tires combined with volatile gases given off by a severely overheated tire and exploded upon reaching autoignition temperature. The use of an inert gas for tire inflation will eliminate the possibility of a tire explosion.^[2]

Motorcycle

There are many different types of motorcycle tires:

Sport Touring - These tires are generally not used for high cornering loads, but for long straights, good for riding across the country.

Street - For sport bikes that are generally not going to be riding aggressively. Riders of this type usually want tires that are going to last a few more miles.

Sport Street - These tires are for aggressive street riders that spend most of their time carving corners on public roadways. These tires do not have a long life, but in turn have very good traction in high speed cornering.

Track or Slick - These tires are for track days or races. They have more of a triangular form, which in turn gives a larger contact patch while leaned over. These tires are not recommended for the street by manufactures, and are known to have a shorter life on the street. Due to the triangulation of the tire, there will be less contact patch in the center, causing the tire to develop a flat spot quicker when used to ride on straightaways for long periods of time.

Construction types

Bias

Mexican Bias Tire, branded as Uniroyal

Bias tire construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows for the entire tire body to flex easily providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic makes for major disadvantages of a bias tires: increased rolling resistance and less control and traction at higher speeds.

Belted bias

A belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. However the plies and belts are at different angles, which lessens performance compared to radial tires.

Radial

Main article: Radial tire

Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stiff stabilizer belts directly beneath the tread. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. A disadvantage of the radial tire is that it produces a harder ride at low speeds on rough roads.

Solid

Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types of light industrial vehicles, carts, and trailers. One of the most common applications for solid tires is for material handling equipment (forklifts). Such tires are installed by means of a hydraulic press.

Semi-pneumatic

Tires that are hollow, but are not pressurized have also been designed for automotive use, such as the Tweel (a portmanteau of tire and wheel) which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but the interior has special compressible polyurethane springs to contribute to a comfortable ride. Besides offering run-flat capability, the tires are intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered by low profile tires. They have not yet been delivered for broad market use.

Performance metrics

Tread wear

Friction between the tire and the roadway causes the tread rubber to wear away over time. Government standards prescribe the minimum allowable tread depth for safe operation. There are several types of abnormal tread wear. Poor wheel alignment can cause excessive wear of the innermost or outermost ribs. Over inflation can cause excessive wear to the center of the tread. Under inflation can cause excessive wear to the outer ribs. Tire manufacturers and car companies have mutually established standards for tread wear testing that include measurement parameters for tread loss profile, lug count, and heel-toe wear. Also can be known as tire wear. See also TKPH below.

Dry traction

Dry traction is measure of the tire’s ability to deliver traction, or grip, under dry conditions. Dry traction increases in proportion to the tread contact area. Dry traction is also a function of the tackiness of the rubber compound.

Wet traction

Wet traction is measure of the tire’s ability to deliver traction, or grip, under wet conditions. Wet traction is improved by the tread design’s ability to channel water out of the tire footprint and reduce hydroplaning.

Force variation

The tire tread and sidewall elements undergo deformation and recovery as they enter and exit the footprint. Since the rubber is elastomeric, it is compressed during this cycle. As the rubber deforms and recovers it imparts cyclical forces into the vehicle. These variations are collectively referred to as Tire Uniformity. Tire Uniformity 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 Uniformity Machines are used to measure geometric parameters including Radial Runout, Lateral Runout, and Sidewall Bulge in the tire factory at the end of the manufacturing process as a quality check.

Balance

When a tire is rotated it will exert a centrifugal force characteristic of its center of gravity. This cyclical force is referred to as balance, or imbalance or unbalance. Tires are checked at the point of manufacture for excessive static imbalance and dynamic imbalance using automatic Tire Balance Machines. Tires are checked again in the auto assembly plant or tire retail shop after mounting the tire to the wheel. Assemblies that exhibit excessive imbalance are corrected by applying balance weights to the wheels to counteract the tire/wheel imbalance.

To facilitate proper balancing, most high performance tire manufacturers place red and yellow marks on the sidewalls of its tires to enable the best possible match-mounting of the tire/wheel assembly. There are two methods of match-mounting high performance tire to wheel assemblies using these red (Uniformity) or yellow (Weight) marks[1].

Centrifugal growth

A tire rotating at high speed will develop a larger diameter due to centrifugal forces that force the tread rubber away from the axis of rotation. As the tire diameter grows the tire width decreases. This centrifugal growth can cause rubbing of the tire against the vehicle at high speeds. Motorcycle tires are often designed with reinforcements aimed at minimizing centrifugal growth.

Rolling resistance

Main article: Rolling resistance

Rolling resistance is the resistance to rolling caused by deformation of the tire in contact with the roadway. As the tire rolls, tread enters the contact area and is deformed flat to conform to the roadway. The energy required to make the deformation depends on the inflation pressure, rotating speed, and numerous physical properties of the tire structure, such as spring force and stiffness. Tire makers seek lower rolling resistance tire constructions in order to improve fuel economy in cars and especially trucks, where rolling resistance accounts for a high amount of fuel consumption.

Stopping distance

The use of performance oriented tires, which have a tread pattern and rubber compounds designed to grip the road surface, usually has slightly shorter stopping distances. However, specific braking tests are necessary for data beyond generalizations.

TKPH

Ton kilometre per hour (TKPH) is the measurement of the work load of a tire and is used for monitoring its work so that it is not put under undue stress which may lead to its premature failure.^[3] The measurement's appellation and units are the same; it is not part of the metric system even though it uses its base units. The recent shortage and increasing cost of tires for heavy equipment has made TKPH an important parameter in tire selection and equipment maintenance for the mining industry. For this reason tire manufacturers of large earth-moving and mining vehicles assign TKPH ratings to their tires based on their size, construction, tread type, and rubber compound.^[4][5] The rating is based on the weight and speed that the tire can handle without overheating and causing it to deteriorate prematurely. The equivalent measure used in the United States is ton mile per hour (TMPH).

Sound and vibration characteristics

Main article: Roadway noise

The design of treads and the interaction of specific tire types with the roadway surface type produces considerable effect upon sound levels or noise pollution emanating from moving vehicles. These sound intensities increase with higher vehicle speeds.^[6] There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and its interaction with the roadway surface type.

Regulatory bodies

Department of Transportation

The United States Department of Transportation (DOT) is the governmental body authorized by congress to establish and regulate transportation safety in the USA.

National Highway and Traffic Safety Administration

The National Highway and Traffic Safety Administration (NHSTA) is a government body within the Department of Transportation tasked with regulating automotive safety.

Uniform Tire Quality Grading System

The Uniform Tire Quality Grading System (UTQG), is a system for comparing the performance of tires, established by the United States National Highway Traffic Safety Administration according to the Code of Federal Regulations 49 CFR 575.104. The UTQG standard rates tires according tread wear, traction, and temperature.

Tire and Rim Association

The Tire and Rim Association (T&RA) is a standards organization authorized to establish tire and wheel manufacturing standards for all tires and wheels manufactured in the United States.

European Tyre and Rim Technical Organization

The European Tyre and Rim Technical Organization (ETRTO) is the standards organization authorized by the European Union to establish and regulate tire and wheel manufacturing standards for all tires manufactured or sold in the European Union.

Japanese Automotive Tire Manufacturer’s Association

The Japanese Automotive Tire Manufacturer’s Association (JATMA) is the standards organization authorized to establish and regulate tire and wheel manufacturing standards for all tires manufactured or sold in Japan. l

TREAD Act

The Transportation Recall Enhancement, Accountability and Documentation Act (or TREAD) Act is a United States federal law sets standards for reporting incidents related to unsafe product defects.

RFID tags

Radio frequency identification tags (RFID) are passive transponders affixed to the inside of the tire for purposes of automatic identification. Tags are encoded with various types of manufacturing data, including the manufacturer’s name, location of manufacture, tire type, manufacturing date, and in some cases test data. RFID transponders can remotely read this data automatically. RFID tags are used by auto assemblers to identify tires at the point of assembly to the vehicle. Fleet operators utilize RFID as part of tire maintenance operations.

Safety

Proper tire safety requires attention to inflation pressure, tread depth, and tire repair. Over inflated tires can burst when subjected to excessive load due to cornering or ride disturbances. Under inflated tires can suddenly go flat and make the vehicle difficult to control. Excessive tire wear will reduce steering and braking response. Treads worn down to the carcass can also burst due to loss of air pressure. Tire inflation pressure and tread depth should be checked regularly in accordance with the manufacturer’s recommendations. Tires should be repaired only by experienced tire repair shops and in accordance with the manufacturer’s recommendations. Ford now recommends that tires greater than six years old be replaced, regardless of tire wear, to reduce the risk of tire failure.^[7]

Penny Test - test for safe tread depth

A US penny can be used to check tire tread to see if it's down to 1/16 or 2/32 of an inch.

• Take a penny and put Lincoln's head into one of the grooves of the tire tread.
• If part of his head is covered by the tread, you're driving with the legal amount of tread.
• If you can see all of Lincoln's head, it's time to replace the tire.

Similar size coins to the US penny, (which has a diameter of .75 inches), of other currencies with heads on the obverse can also be used, depending on the legal minimum tire requirements of each individual country. However, a much more useful test, for those outside of the USA, is to insert the head of an unused match into the tyre's tred, if the tred is at any point below 3/4 of the head the tyre should be replaced, this test is most common in the EU, Australasia, and Asia.

The November 2007 issue of "Consumer Reports" magazine, (page 60), stated that based on tests they conducted; tires should be replaced when the tire tread is down to 1/8 inch. This is about the distance to George Washington's hairline on a US quarter. The tire that just passes the "penny test" could be dangerous when driving in snow or when hydroplaning.

References

External links

• Car Bibles : The Wheel and Tyre Bible
• Calculate replacement wheel/tire size combos and related speedometer reading changes
• All available wheel/tire sizes for your car from a database
• How to decode alphanumeric tire codes
• Interactive comparison of Tire and Wheel Sizes
• How to locate and read tire codes
• Hypervideo of how to remove a car tire
• Tire Recalls and Tire Safety:The RFID Solution. traction