Tire

Ring-shaped covering that fits around a wheel's rim

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"Rubber tires" redirects here. For the film, see Rubber Tires

Assorted new automotive road tires, showing a variety of tread patterns. Tractor tires have substantial ribs and voids for traction in soft terrain.

A tire (North American English) or tyre (Commonwealth English) is a circular component that encapsulates a wheel's rim to distribute a vehicle's load from the axle, through the wheel, and onto the ground, while ensuring traction on the surface it traverses. Most tires, like those for cars and bikes, are pneumatically inflated structures that offer a flexible cushion to absorb shocks from uneven surfaces. Tires create a footprint known as a contact patch, designed to align with the vehicle's weight, ensuring minimal surface deformation.

Modern pneumatic tires are made from synthetic rubber, natural rubber, fabric, wire, carbon black, and other chemicals. They consist of a tread that provides traction and a body that contains compressed air. Before rubber tires, metal bands around wooden wheels prevented wear. Early rubber tires were solid. Pneumatic tires are now used on cars, bicycles, motorcycles, buses, trucks, heavy equipment, and aircraft. Metal tires are for locomotives, and solid rubber or polymer tires serve in non-automotive roles like casters, carts, lawnmowers, and wheelbarrows.

Poorly maintained tires can pose serious risks, from flat tires rendering vehicles immobile to blowouts causing damage and injuries. Tire manufacturing is heavily regulated. With widespread motor vehicle use, tire waste is a significant global issue. Recycling methods include mechanical reuse for products like crumb rubber and chemical pyrolysis for tire-derived fuels. Improper disposal or burning of tires releases harmful chemicals into the environment, and ongoing tire usage produces microplastics that impact human health.

Etymology and Spelling

The term tire is a short form of attire, implying a 'dressed' wheel. Tyre is historically the oldest spelling. Both terms were used in the 15th and 16th centuries, with tire becoming more common in the 17th and 18th centuries. The spelling tyre reappeared in the 1840s when the British began using malleable iron on railway wheels. The 1911 Encyclopædia Britannica noted that 'tyre' was not accepted by top English authorities and was unrecognized in the US. Despite such remarks, by the 20th century, tyre had become standard in British usage.

History

The earliest tires were made from leather, then iron, placed on wooden wheels for carts and wagons. Skilled workers, known as wheelwrights, heated and expanded the tires to fit them tightly on wheels. The first patent for a pneumatic tire appeared in 1847 by Robert William Thomson but didn't go into production. However, in 1888, John Boyd Dunlop created the first practical pneumatic tire in Belfast to prevent his son's headaches from riding on rough pavements. His design proved superior, with Willie Hume winning races in Ireland and England in 1889 using Dunlop's tires.

Dunlop’s patent faced challenges and was declared invalid in 1892 due to Thomson's prior art. Nonetheless, Dunlop is credited for advancing the pneumatic tire. The technology depended on various innovations, including natural rubber vulcanization and the "clincher" rim design.

Synthetic rubbers emerged in the 1920s from Bayer’s labs. During WWII, the UK explored alternatives to rubber tires, considering materials like leather and rayon. In 1946, Michelin introduced radial tire construction, which improved handling and fuel efficiency. This technology spread in Europe and Asia and was later adopted in the U.S.

Applications

Tires are classified based on the vehicles they support, the load they bear, and their application, such as motor vehicles, aircraft, or bicycles.

Automotive

Light–Medium Duty

Passenger vehicle tires handle loads of 550 to 1,100 pounds (250 to 500 kg) per drive wheel, while light-duty trucks and vans manage 1,100 to 3,300 pounds (500 to 1,500 kg). Variants include winter tires, light truck tires, all-season tires, and high-performance tires, among others.

• Snow tires have larger gaps than summer tires, improving traction on snow and ice. Some feature studs for enhanced grip. Regulations for snow tire use differ globally.
• All-season tires are quieter on roads but less effective in snow or ice compared to dedicated snow tires.
• All-terrain tires offer off-road grip while being suitable for highway use.
• Mud-terrain tires have open tread designs for mud but perform poorly on pavement.
• High-performance tires are rated for high speeds but trade-off durability and comfort.
• Electric vehicle tires have unique requirements due to weight, torque, and rolling resistance needs.

Other light-duty tires include run-flat and race car tires.
Run-flat tires eliminate the need for a spare by supporting the vehicle at reduced speeds after a puncture. Conventional vehicles use spare tires.
Race car tires maximize grip but wear out quickly, with variants for dry and wet conditions.

Heavy Duty

Heavy-duty tires, for large trucks and buses, can carry loads ranging from 4,000 to 5,500 pounds (1,800 to 2,500 kg) per drive wheel. They're often mounted in tandem.

• Truck tires come in various profiles, including "low profile" and "super-single."
• Off-road tires are used in construction, agriculture, and forestry, offering deep, wide treads for loose terrain.

Other

Aircraft, bicycle, and industrial tire designs meet distinct requirements.

• Aircraft tires are light and radial for landing on pavements. Some light aircraft use low-pressure tundra tires for rough terrain.
• Bicycle tires cater to different terrains, supporting clincher, wired, and tubular types.
• Industrial tires support forklifts, tractors, and excavators, often featuring solid or foam-filled constructions for durability.
• Motorcycle tires ensure traction and rider comfort, resisting wear and absorbing shocks.

Construction Types

Pneumatic tires are used across a range of automotive and non-automotive applications, including cars, trucks, and aircraft. Non-automotive uses include slow-moving or light-duty scenarios with solid tires.

Automotive

Following Consumer Reports' 1968 endorsement of radial tires, radial technology became standard, reaching 100% market share in North America by the 1980s.

Radial construction involves body ply cords placed at right angles to the tread's centerline and parallel to each other. Benefits include longer tread life, improved steering, and fuel economy. However, they offer a harsher ride on rough roads.

Bias tire construction features body ply cords extending diagonally from bead to bead. This offers smoother rides on rough surfaces but increases rolling resistance and reduces high-speed traction.

A belted bias tire combines bias plies with stabilizer belts for a smoother ride and lower rolling resistance. Goodyear popularized this design with its "Polyglas" tire.

Other

Tubeless tires don't need an inner tube. Semi-pneumatic tires have a hollow, non-pressurized center, offering lightweight, puncture-proof, and cushioning characteristics. Airless tires, used in high-puncture-risk scenarios, are made from solid rubber or plastics. These are common in industrial applications, like forklifts.

Wooden wheels for horse-drawn vehicles typically use wrought iron tires, extended to tramways. Railway wheels often use steel tires to avoid replacing entire wheels. Aircraft tires may exceed 200 psi, sometimes using nitrogen to prevent oxidation and explosions.

Manufacturing

Pneumatic tires are produced in about 450 factories worldwide, beginning with raw materials like rubber and chemicals. As of recent years, the global tire market is growing, with projections indicating a rise from $126 billion in 2022 to $176 billion by 2027.

Top tire manufacturers include Bridgestone, Michelin, and Goodyear. The Lego Group holds the record for the highest annual tire production.

Components

A tire is made up of various components, including the tread, bead, sidewall, shoulder, and ply.

Tread

The tread is the part of the tire in contact with the road. It's made of thick rubber for traction and durability. Different treads are designed for various conditions, such as deep slots for snow or smooth surfaces for racing.

Wear bars indicate when a tire's tread is worn out, usually at a depth of 1.6 mm.

Other

The tire bead contacts the wheel rim, ensuring a secure fit and maintaining air pressure. The sidewall bridges the tread and bead, reinforced with fabric or steel for strength. The shoulder forms the transition from tread to sidewall. Plies are layers of cords embedded in the rubber to maintain shape and strength.

Blems

Blem tires, which fail inspection for aesthetic reasons, are sold at a discount but are fully functional with warranties.

Materials

Modern pneumatic tires consist of cords for strength and elastomers like the styrene-butadiene copolymer for durability.

Cords

Cords made of steel, natural, or synthetic fibers provide tensile strength. Good adhesion between cords and rubber is critical, often achieved through additives and coatings.

Elastomer

The elastomer forms the tread and encases cords. It is key to rolling resistance and traction. Balancing low rolling resistance for fuel efficiency with high wet traction for safety is a significant challenge. The most common material is a styrene-butadiene copolymer, combining properties of rubbery polybutadiene and glassy polystyrene.

Tire wear generates particulate emissions, contributing to pollution.

On the Wheel

Tire-associated components include the wheel, valve stem, and sometimes an inner tube for air pressure maintenance.

Performance Characteristics

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The interactions of a tire with the pavement are complex. A commonly used empirical model is Pacejka's "Magic Formula." Some dynamics and forces include:

Dynamics

• Balance– Even mass distribution ensures tire balance. Imbalances are corrected with weights or internal balancing agents.
• Centrifugal growth – High speeds can cause the tire diameter to expand, leading to speedometer errors and potential tire rubbing.
• Pneumatic trail– The distance between resultant side-slip force and the geometric center of the contact patch.
• Slip angle– The angle between the tire’s actual direction and pointing direction.
• Relaxation length– Delay between slip angle introduction and steady-state cornering force.
• Spring rate– Ratio of vertical force to tire deflection, influencing suspension performance. Inflation pressure affects it.
• Stopping distance– Performance tires have shorter stopping distances but require specific tests for accuracy.

Forces

• Camber thrust– Lateral force from rolling tire due to camber angle.
• Circle of forces– Visualizing dynamic interaction between tire and road surface.
• Contact patch– Area transmitting forces via friction, affecting steering.
• Cornering force– Side force from tire during cornering.
• Dry traction– Tire's grip ability in dry conditions, depending on rubber tackiness.
• Force variation– Cyclical forces from deformation and recovery measured during manufacturing.
• Rolling resistance– Resistance from tire deformation affecting fuel economy. Pneumatic tires have lower resistance compared to solid ones.
• Self-aligning torque– Torque created while rolling, steering the tire.
• Wet traction– Grip in wet conditions, improved by tread design to channel water out. Racing bicycle tires, when properly inflated, avoid hydroplaning.

Load

• Load sensitivity– Behavior under load, where the coefficient of friction decreases as vertical load increases.
• Work load– Monitored using metrics like Ton Kilometer Per Hour (TKPH), significant for tire selection and maintenance.

Wear

Tire wear contributes to rubber pollution and is unregulated compared to exhaust emissions.

Tread wear

Occurs through normal use; various causes include poor alignment, rough terrain, over or under-inflation, and unbalanced wheels, leading to uneven wear.

Tread wear indicators (T.W.I.)

Bars indicating worn tread, required in new tires since 1968 in the US.

Damage by aging

Causes include UV exposure, heat, and flex fatigue. Proper storage slows but doesn’t prevent degradation.

Sizes, Codes, Standards, and Regulatory Agencies

Automotive tires display identifying markings, indicating size, ratings, and more.

Americas

The National Highway and Traffic Safety Administration (NHTSA) regulates automotive safety in the U.S., including tire performance and aging. T&RA sets voluntary standards for tire dimensions and load/inflation standards.

Europe

The European Tyre and Rim Technical Organisation (ETRTO) establishes engineering dimensions and guidelines. All road-used tires in Europe must carry an E-mark. The British Rubber Manufacturers Association (BRMA) recommends replacing tires over ten years old.

Asia

The Japanese Automobile Tire Manufacturers Association (JATMA) and China Compulsory Certification (CCC) regulate tire and product safety.

Maintenance

A tire repair shop in Niger

Maintaining tire health involves rotation, alignment, and occasionally retreading.

• Rotation– Evening out wear by moving tires to different vehicle positions.
• Alignment– Ensuring wheels rotate in the vehicle's direction, preventing irregular wear. It involves camber, caster, and toe angle adjustments.

Inflation

Rolling resistance as a function of tire inflation

Proper inflation is crucial for wear and rolling resistance. Vehicle manufacturers provide specifications, typically stamped on the tire or vehicle, indicating optimal pressures.

• Specification– Ensuring safe operation within load ratings, found in vehicle manuals or door decals.
• Ground contact– Overinflation and underinflation affect the tire contact patch and wear patterns. Increased pressure might reduce resistance but shorten the stopping distance. Under-inflation raises rolling resistance and friction.
• Monitoring– Tire pressure monitoring systems alert drivers if pressure drops below safe limits, using both direct and indirect measurement methods.

Hazards

Tire failures or loss of traction pose significant risks. Manufacturing errors have led to recalls, such as the Firestone-Ford controversy.

Tire Failure

• Belt separation– Caused by excessive deflection, high pavement temperatures, or maintenance/storage issues.
• Non-belt separations– Involving the tread, bead, or sidewall, or reinforcement materials.
• Other failures include run-flat damage, chemical degradation, cracking, indentations, and bulges.

Vehicle Operation Failures

• Melting rubber– Heat from friction can melt rubber, reducing traction.
• Hydroplaning– Loss of contact on wet surfaces, causing slipping. Dynamic hydroplaning involves standing water and speed, while viscous hydroplaning involves melted tire rubber.
• Snow– Traction in snow relies on compacting snow for strength, involving frictional contact between tread and snow.
• Ice– Low friction due to smooth texture and near-melting point conditions.
• Soft ground– Water-lubricated soil reduces shear strength, and dry sand lacks cohesiveness.

Health Impacts

Tires contain