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Tires, or tyres (in American and British English, respectively), are ring-shaped parts, either pneumatic or solid (including rubber, metals and plastic composites), that fit around wheels to protect them and enhance their function.
Pneumatic tires are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft.
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Encyclopedia
Tires, or tyres (in American and British English, respectively), are ring-shaped parts, either pneumatic or solid (including rubber, metals and plastic composites), that fit around wheels to protect them and enhance their function.
Pneumatic tires are used on many types of vehicles, such as bicycles, motorcycles, cars, trucks, earthmovers, and aircraft. Tires enable better vehicle performance by providing traction, braking, steering, and load support. Tires form a flexible cushion between the vehicle and the road, which smooths out shock and makes 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, carried out this work. The outer ring served to "attire" the wheel for use, providing a wear-resistant surface to the perimeter of the wheel. The word "tire" thus emerged as a variant spelling to refer to the metal bands used to dress wheels.
Tire is an older spelling than tyre, but both were used in the 15th and 16th centuries for a metal tire; tire became the settled spelling in the 17th century. In the UK, tyre was revived in the 19th century for pneumatic tyres, possibly because it was used in some patent documents, though many continued to use tire for the iron variety. The Times newspaper was still using tire as late as 1905.
The first practical pneumatic tire was made by the Scot, John Boyd Dunlop, in 1887 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).
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
- 1888 – First commercial pneumatic bicycle tire produced by Dunlop
- 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
- 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 black to the rubber
- 1919 – Goodyear and Dunlop announced pneumatic truck tires
- 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
For a list of tire companies and the dates they were established, see List of Tire Companies.
Terms
Tread
The tread is the part of the tire which comes in contact with the road surface. The tread is a thick rubber, or rubber/composite compound formulated to provide an appropriate level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, lugs, voids and sipes. 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 (or non-uniform) lug sizes circumferentially in order to minimize noise. Sipes are valleys cut across the tire, usually perpendicular to the grooves, which allow the water from the grooves to escape to the sides in an effort to prevent hydroplaning.
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 (M&S) tires are designed with higher void ratios to channel away rain and mud, while providing better gripping performance.
Treadwear
The treadwear grade describes how long the tire manufacturers expects the tire to last. A Course Monitoring Tire (the standard tire that a test tire will be compared to) has a rating of "100". If a manufacturer assigns a treadwear rating of 200 to a new tire, they are indicating that they expect the new tire to have a useful lifespan that is 200% of the life of a Course Monitoring Tire. In general, manufacturers tend to overstate the treadwear of their tires in an effort to create the impression that their tires last a long time. The ability of manufacturers to report their own numbers makes comparison of treadwear ratings between companies useless. Ratings may still be useful within a manufacturer's own line of tires.
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, 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 on clean, dry pavement.
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 wet or icy conditions.
Wear bar
Wear bars (or wear indicators) are raised features located at the bottom of the tread grooves that indicate the tire has reached its wear limit. 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
The contact patch, or footprint, of the tire, is merely the area of the tread which is in contact with the road surface. This is the area which 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 which contacts the rim on the wheel. The bead is reinforced with steel wire, and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. The bead fit is tight, to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship to the tire is a factor in the handling characteristics of an automobile, because the rim supports the tire's profile.
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. The sidewall, in conjunction with the air inflation, also supports the load of the vehicle. Sidewalls are molded with manufacturer-specific detail, government mandated warning labels, and other consumer information, and sometimes decorative ornamentation.
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 Singapore, tires degrade sooner than in temperate climates. Tires on seldom-used trailers are at the greatest risk of age-failure, but some tires are built to withstand idleness, usually with nylon reinforcement. In the past rayon was used in tires, but it ages quite quickly.
Shoulder
The shoulder is that part of the tire at the edge of the tread as it makes transition to the sidewall.
Inner tube
Almost all bicycle tires, many motorcycle tires, and many tires for large vehicles such as buses, heavy trucks and tractors are designed for use with inner tubes. Inner tubes are torus-shaped balloons made from an impermeable material, such as soft, elastic synthetic rubber, to prevent air leakage. The inner tubes are inserted into the tire and inflated to retain air pressure.
Wheel
Tires are mounted to wheels that bolt to the hub. The beads of the tire are held on the wheel's rim largely by the internal tire force from the air pressure. Automotive wheels are typically made from pressed and welded steel, or a composite of lightweight metal alloys, such as aluminum or magnesium. These alloy wheels may be either cast or forged.
Valve stem
The valve stem is a tube made of steel or rubber 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 of the valve stem at regular intervals reduces the chance of failure.
Tire pressure monitoring system
Tire pressure monitoring systems (TPMS) are electronic systems that monitor the tire pressures on individual wheels on a vehicle, and alert the driver 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.
Inflation pressure
Tires are specified by the vehicle manufacturer with a recommended inflation pressure, which permits safe operation within the specified load rating and vehicle loading. Most tires are stamped with a maximum pressure rating (for USA only). For passenger vehicles and light trucks, the tires should be inflated to what the vehicle manufacturer recommends, which is usually located on a decal just inside the driver's door, or in the vehicle owners handbook. Tires should not be inflated to the pressure on the sidewall; this is the maximum pressure, rather than the recommended pressure.
If tire pressure is too high, the tire contact patch is reduced, which decreases rolling resistance. However, ride comfort is reduced, but traction is not always reduced, stopping distance is not always increased. Also, going above max sidewall pressure rarely results in the center of the tire wearing more than the shoulder.
If tire pressure is too low, the tire contact patch is increased, increasing rolling resistance, tire flexing and friction between the road and tire. This "underinflation" can lead to tire overheating, premature tread wear, and tread separation in severe cases. Braking distance did not statistically change as tire pressure increased, suggesting that a larger contact patch from underinflation may not be a significant contributor for the conditions explored in these specific tests.
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.
Replacing a tire on a vehicle with one with a lower load rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
Speed rating
The speed rating denotes the maximum speed at which a tire is designed to be operated. For passenger vehicles these ratings range from 99 mph (160 km/h) to 186 mph (300 km/h). For a table of speed ratings, see tire code.
Replacing a tire on a vehicle with one with a lower speed rating than originally specified by the vehicle manufacturer will often render the insurance invalid.
Service rating
Tires (especially in the USA) are often given service ratings, mainly used on bus and truck tires. Some ratings are for long-haul, and some for stop-start multi-drop type work. Tires designed to run 500+ miles per day carrying heavy loads require special specifications.
Rotation
Tires may exhibit irregular wear patterns once installed on a vehicle and partially worn. Furthermore, front-wheel drive vehicles will wear the front tires at a greater rate compared to the rears. 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
When mounted on the vehicle, the wheel and tire may not be perfectly aligned to the direction of travel, and therefore may exhibit irregular wear. If the discrepancy in alignment is large, then the irregular wear will become quite substantial if left uncorrected.
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
Tires that are fully worn can be re-manufactured to replace the worn tread. This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread. Retreading is economical for truck tires because the cost of replacing the tread is less than the price of a new tire. Retreading passenger tires is less economical because the cost of retreading is high compared to the price of a new tire. However, commercial truck drivers run the risk of "blow-outs", separation, and tread peeling from the casing, due to re-use of the tire casing. To reduce these problems, tire technicians and the retread plant must ensure the casing is in the best condition possible. Tires or casings with problems such as capped tread, tread separation, corroded belts or sidewall damage, or any run-flat or skidded tires, will be rejected.
In most situations, retread tires can be driven under the same conditions and at the same speeds as new tires with no loss in safety or comfort. The percentage of retread failures should be about the same as for new tire failures, but many drivers, including truckers, are guilty of not maintaining proper air pressure on a regular basis and if a tire is abused (overloaded, underinflated, or mismatched to the other tire on a set of duals), then that tire (new or recapped) will fail.
Many commercial trucking companies put retreads only on trailers, using only new tires on their steering and drive wheels. This procedure increases the driver's chance of maintaining control in case of problems with a retreaded tire.
Flat
A flat tire occurs when a tire deflates to the point where the metal of the wheel rim comes to ground level. This can occur as a result of normal wear-and-tear, a leak, or more serious damage. A tire which has lost sufficient pressure to cause it to become distorted at the bottom will impair the stability of the vehicle and may damage the tire further if it is driven in this condition. The tire should be changed and/or repaired before it becomes completely flat. Continuing to drive a vehicle with a flat tire will damage the tire beyond repair, possibly damage the rim and vehicle, and put the occupants and other vehicles in danger. A flat tire or low-pressure tire should be considered an emergency situation, requiring immediate attention to rectify the problem. (Some tires, known as "run-flat" tires, have either extremely stiff sidewalls or a resilient filler to allow driving a limited distance while flat, usually at reduced speed, without permanent damage or hazard.)
Hydroplaning (or aquaplaning)
Hydroplaning, also known as aquaplaning, is the condition where a layer of water builds up between the tire and road surface. Hydroplaning occurs when the tread pattern cannot channel away enough water at an adequate rate to ensure a dry footprint area. When hydroplaning occurs, the tire effectively "floats" above the road surface on a cushion of water - and loses traction, braking and steering, creating a very unsafe driving condition. When hydroplaning occurs, there is considerably less responsiveness of the steering wheel. The correction of this unsafe condition is to gradually reduce speed, by merely lifting off the accelerator/gas pedal.
Hydroplaning becomes more prevalent with wider tires.
Markings
DOT Code
In the United States, 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 plant code (two numbers or letters) 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 after the DOT code. Thus, a tire manufactured in the 17th week of 1998 would have the code 178?. 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 for road use in Europe after July 1997 must carry an E-mark. The mark itself is either an upper case "E" or lower case "e" - followed by a number in a circle or rectangle, followed by a further number. An (upper case) "E" indicates that the tire is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30. A (lower case) "e" 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
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, and more often, a more "sporty" driving style. They feature a softer rubber compound for improved traction, especially on high speed cornering. The trade off of this softer rubber is shorter 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, or M&S), is a classification for specific winter tires designed to provide improved performance under low temperature conditions, compared to all-season tires. 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).
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 and rallying.
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 mud and 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 surface, thus allowing the tires to penetrate the snow layer and grip harder snow or road surface beneath. This does not compensate when the snow is too deep for such penetration.
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 but rarely with a snowflake. 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
Some vehicles carry a spare tire, already mounted on a wheel, to be used in the event of flat tire or blowout. Minispare, or "space-saver spare" tires are smaller than normal tires to save on trunk/boot space, gas mileage, weight and cost. Minispares have a short life expectancy, and low speed rating.
Run-flat
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 typically feature strong, load-supporting sidewalls. An infamous example of an alternate run flat technology has plastic load-bearing inserts attached to the rim instead of the reinforced sidewalls.
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 buses. 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 wheel loaders, backhoes, graders, trenchers, and the like; as well as large mining trucks. OTR tires can be of either bias or radial construction although the industry is trending toward increasing use of radial. Bias OTR tires are built with a large number of reinforcing plies to withstand severe service conditions and high loads.
Dramatically increasing commodity prices has led to shortages of new tires. As a consequence, multi-million dollar trucks can be idled for lack of tires, costing mines millions of dollars in lost productivity. This has led to a stronger effort to recycle old OTR tires. As of 2008, a new OTR tire can cost up to $50,000; retread tires are sold at half the price of new tires, and last 80% as long. Retreading an OTR tire is labor intensive. First, the retreading technician must place the old tire in a buffing machine to remove what remains of the old tread; "skiving" follows this, which is the removal, by hand, of material the buffing misses. Next, the technician must inspect the tire, repairing defects. Lastly, the technician fills holes in the tire with rubber, applies a cement gum adhesive, and places the tire on a machine which will apply a new tread.
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
Racing tires are highly specialized according to vehicle and race track conditions. This classification includes tires for top-fuel dragsters, drift racers, extreme off-road racing, oval-track racers, jet-powered trucks, and monster trucks - as well as the large-market race tires for Formula One, NASCAR, rallying, MotoGP and the like. Tires are specially engineered for specific race tracks according to surface conditions, cornering loads, and track temperature. Tires also have been specially engineered for "drifting" in which vehicles engage in exaggerated skids and slides. Racing tires often are engineered to minimum weight targets, so tires for a 500 mile race may run only 100 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 to attract customers with racing dreams.
Racing tires often are not legal for normal highway use.
Industrial
The Industrial tire classification is a bit of a catch-all category and includes pneumatic and non-pneumatic tires for specialty industrial and construction equipment such as skid loaders and fork lift trucks.
Bicycle
This classification includes all forms of bicycle tires, including road racing tires, mountain bike tires, snow tires, and tubular tires.
Aircraft
Aircraft tires are designed to withstand extremely heavy loads for short durations. The number of tires required for aircraft increases with the weight of the plane (because the weight of the airplane is distributed better). Aircraft tire tread patterns are designed to facilitate stability in high crosswind conditions, to channel water away to prevent hydroplaning, and for braking effect. Aircraft tires are usually inflated with nitrogen or helium in order to minimize expansion and contraction from extreme changes in ambient temperature and pressure 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. Tests of airline aircraft tires have shown that they are able to sustain pressures of maximum 800 psi (55.2 bar) before bursting. During the test the tires have to be filled with water, instead of helium or nitrogen which is the common content of aircraft tires, to prevent the test room being blown apart by the pressure when the tire bursts.
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.
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.
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 better traction in high speed cornering. Street and sport street tires have good traction even when cold, but when warmed too much, can actually lose traction as their internal temperature increases.
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 and have no tread so they lose almost all grip in the wet. Racing slicks are also made of a harder rubber compound and do not provide as much traction as street tires until warmed to a higher internal temperature than street tires normally operate at. Most street riding will not put a sufficient amount of friction on the tire to maintain the slicks optimal tire temperature, especially in colder climates and in spring and fall.
Construction types
Bias
Bias tire (or cross ply) 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 the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: 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
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. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability and lower grip ability at low speeds.
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 tire 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 characteristics
Tread wear
Friction between the tire and the road surface causes the tread rubber to wear away over time. Government legal 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. Gravel roads, rocky terrain, and other rough terrain will cause accelerated wear. Over inflation above the sidewall max can cause excessive wear to the center of the tread. However, inflating up to the sidewall limit will not cause excessive wear in the center of the tread. Modern tires have steel belts built in to prevent this. Under inflation causes excessive wear to the outer ribs. Quite often the placard pressure is too low and most tires are underinflated as a result. Unbalanced wheels can cause uneven tire wear, as the rotation may not be perfectly circular. 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. However, tires with a circular cross-section, such as those found on racing bicycles and motorcycles, when properly inflated have a sufficiently small footprint to not be susceptible to hydroplaning. For such tires, it is observed that fully slick tires will give superior traction on both wet and dry pavement.
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 wheel and tire is rotated, it will exert a centrifugal force characteristic of its center of gravity. This cyclical force is referred to as balance, and a non-uniform force is referred to as 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.
Centrifugal growth
A tire rotating at higher speeds will tend to 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
Rolling resistance is the resistance to rolling caused by deformation of the tire in contact with the road surface. 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.
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.
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. 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. 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
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. 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
DOT
The United States Department of Transportation (DOT) is the governmental body authorized by congress to establish and regulate transportation safety in the USA.
NHTSA
The National Highway and Traffic Safety Administration (NHTSA) is a government body within the Department of Transportation tasked with regulating automotive safety.
UTQG
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.
T&RA
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.
ETRTO
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.
JATMA
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.
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 vehicle safety requires specific attention to tires - to inflation pressure, tread depth, and general tire condition. Over inflated tires run the risk of explosive decompression (they can pop). Under inflated tires have a hgher rolling resistance and suffer from rapid tread wear on the edges of the tread. Excessive tire wear will reduce steering and braking response. Tires worn down past their safety margins and into the casing run the very real risk of rupturing. Tire inflation pressure and tread depth should be checked regularly in accordance with the vehicle manufacturer’s recommendations. Certain combinations of cross ply and radial tires on different wheels of the same vehicle can lead to vehicle instability, and may also be illegal. UV light from the sun or even welding equipment can 'age' tires and make them more liable to burst. Ford now recommends that tires in service greater than six years should be replaced, regardless of tire wear, to reduce the risk of tire failure (although this is not mandatory).
Tires should be repaired only at experienced tire repair shops, and in accordance with the manufacturer’s recommendations.
A US penny can be used to check tire tread to see if it is 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 are driving with the legal amount of tread.
- If you can see all of Lincoln's head, it is 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 tire's tread; if the tread is at any point below 3/4 of the head, the tire should be replaced. This test is most common in the EU, Australasia, and Asia.
US and European tires have 'wear bars', or "Tread Wear Indicators" (TWI) moulded into the grooves of the tire. When these become flush with the tops of the remaining tread, the tire is at the legal limit of normal safety and must be replaced. Certain European countries have stricter limits on tread wear compared to other European countries.
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.
Dangers of aged tires
Research and tests show that as tires age, they begin to dry out and become potentially dangerous, even if unused. Aged tires may appear to have similar properties to newly manufactured tires; however once the vehicle is traveling at high speeds (i.e. on a freeway) the tread could peel off, leading to severe loss of control and perhaps a rollover.
The date of a tire's manufacture is found on the sidewall to the right of the product code. The date code is often found on the inward side of the tire, so if they are already installed on the vehicle, a person has to lie underneath the car with a flashlight to check the dates. The date is a four digit code WWYY, with WW denoting the week (1-52) and YY denoting the year. Tires made in the US have this code as the last four numbers of the "D.O.T." code.
Many automakers recommend a six year limit on tires and several tire manufacturers (Bridgestone, Michelin) have called for tires to be removed from service 10 years after the date of manufacture. However, an investigative report by Brian Ross on ABC's 20/20 news magazine found that many major retailers such as Goodyear, Wal-Mart, and Sears were selling tires that had been produced six or more years ago. Currently, no law for aged tires exists in the United States.
See also
- Category:Tires
External links
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