Tyres & Turning | Brief History and Lifecycle of Tyres • EVreporter

Automotive consultant and subject matter expert Mr Prabhat Khare writes about automotive tyres, their many types, and technological upgrades over the years and their lifecycle.

Once, when Shambhasur attacked the heavens, Raja Dashrath was called upon to join the army of Indra, the Lord of Heavens, to allay the attack. Rani Kaikeyi, too, accompanied him. During the war, the axle of the chariot’s wheel broke when Rani Kaikeyi was supposed to have used her finger for the axle till the battle was over. Overwhelmed with gratitude for her timely help, the king bestowed two boons on her. Later, these two boons formed the basis of Ramayana. – From Valmiki Ramayana

Background

The pneumatic tyre is one of human history’s most intricate and vital inventions. Despite its outward simplicity, it’s a marvel of engineering that often goes unnoticed in our daily lives. Without tyres, we would still rely on cumbersome wooden or metal wheels, making modern vehicles like cars, trucks, motorcycles, and bicycles impossible. The world as we know it owes much to the invention of rubber tyres, which have revolutionized travel and transformed global connectivity. Scotsman John Boyd Dunlop created the first practical pneumatic tyres for his son’s bicycle, addressing his son’s discomfort while riding on rough roads. One of the key advantages of pneumatic tyres is their ability to reduce rolling resistance. Unlike solid tyres, internal air pressure allows these tyres to absorb bumps in the road without creating a reactive force. This difference in rolling resistance is easily felt when using wheelchairs or baby buggies equipped with either type. Modern pneumatic tyres are composed of strong, lightweight polymer fibres bonded within a matrix of viscoelastic rubbers. Specialized adhesives combine various components into a lightweight, doughnut-shaped structure called the carcass, with a rubber tread bonded to its outer edge for traction. Radial tyres feature reinforcing belts made of polymer threads or steel wire, while a thin sidewall connects the tread to the steel cables in the bead area, securing the tyre to the wheel. Ultimately, the pneumatic tyre is a durable, cost-effective innovation that enables fast and safe personal transportation, fostering travel independence and a robust network for overland freight delivery.

Basic Theory of The Pneumatic Tires

Historically, with the rise of automobiles in the early 20th century, all sorts and kinds of carriage springs were adopted for travel comforts. Still, most of them were rejected, and on the way to the evolution of wheels, the endless iron hoop that bound the wooden wheels had slowly given way to the rubber tyres, solid, cushion, and pneumatic. The demand for greater speed and comfort in vehicular travel was the need which brought out the pneumatic tyres and provided much greater comfort to the passengers, minimizing vibrations & which was rightly termed as a vibration annihilator. For example, when a pebble or small stone lies in the path of a vehicle whose wheel tyres are of metal, the entire weight of the wheel has to be lifted over the stone at a great expenditure of motive power and at the price of discomfort. When solid or cushion rubber tyres encounter the same obstacle, the elasticity of the rubber determines the conditions governing loss of force, discomfort, etc. Still, when the pneumatic tyres pass over the obstruction, the energy loss and unpleasant vibration can be reduced to a minimum. It simply means that the displacement of the compressed air, for instance, the combined elasticity of the air and the thin covering of rubber, makes this possible. The greater the speed, too, the greater the ease with which the obstruction is overcome. The only disadvantage of a closed rubber tube (tyre) filled with pressurized air, allowing it to overcome any shock, vibration, or jerks while moving on the road, is that it is liable to puncture.

Functions Of Tires

• Vehicle-Road Interface: The primary role of passenger vehicle tyres is to connect the vehicle to the road. The contact area of all four tyres on a typical mid-size vehicle is smaller than 600 cm2(approximately 21.6 cm x 27.9 cm), with each tyre having a footprint roughly the size of an average hand. Despite this small contact patch, we rely on these tyres to ensure safe navigation on sharp turns at exit ramps and smooth handling over any terrain & in any weather conditions.

• Load Support: Tyres are engineered to support a vehicle’s weight, causing them to deform until the internal air pressure balances the load pressure. For example, a standard passenger tyre inflated to 2.45 kg/ cm² would need an average contact area of about 645 cm² to support a 160 kg load. Heavier loads require either a larger contact area (leading to more deflection) or higher tyre pressures. Typically, larger contact areas are associated with larger tyres. Industry standards provide guidance on these specifications.

• Road Surface Friction: The ability of vehicles to accelerate, decelerate, and navigate corners relies heavily on the friction between the tyres and the road. Tire tread designs are crucial for adapting to various weather conditions—whether dry, wet, snowy, or icy. While racing tyres or worn tyres may perform well on dry roads, they can struggle in wet conditions due to hydroplaning[1]. Effective tread designs allow water to escape from the tyre’s contact area to reduce hydroplaning risk, balancing the sometimes conflicting needs for good dry traction, minimal wear, and low noise.

  [1] Hydroplaning occurs when a vehicle’s tyres lose contact with the road due to water, causing a loss of traction and control. Factors include water depth, tire condition, speed, and road surface. To reduce the risk, drive at lower speeds in wet conditions and ensure tyres are in good condition.

• Absorption of Road Irregularities: One of the key advantages of pneumatic tyres is their ability to absorb shocks and irregularities from the road. Tyres function like a spring and damper system, effectively cushioning impacts and enhancing ride comfort across diverse driving conditions.

Criticality & Importance of Pneumatic Tires

The introduction of horseless carriages represented a major technological advancement in transportation. However, early models were fitted with rigid wood or metal tyres, which lacked the flexibility and traction necessary for agile maneuvering. These primitive tires struggled to generate enough lateral force, making turns difficult and possible only at slow speeds. As a result, journeys were often bone-jarring, with rigid tires providing little shock absorption, leading to discomfort for both passengers and drivers. Pneumatic tires have become essential for vehicles, particularly in enabling smooth and efficient turns at higher speeds. Over a century and a half ago, horse-drawn carts dominated the roads, where navigating corners relied heavily on the pulling power of the horses. While horses could guide carts around bends, the process was laborious and limited to slow speeds, hindering overall efficiency. The advent of pneumatic tires transformed the driving experience, significantly enhancing maneuverability and ride comfort. With air-filled rubber tires, vehicles could smoothly navigate corners at higher speeds, dramatically improving handling and performance. This innovation not only made automobiles more practical but also reshaped the landscape of transportation, paving the way for modern vehicles that can execute swift and agile maneuvers.

Basic Variants & Details Of Modern Tires

Basic Structure of Tires

A modern pneumatic tire is a sophisticated composite structure designed for optimal performance and durability. It comprises strong yet lightweight polymer fibers intricately woven into a matrix of viscoelastic rubber polymers. This combination provides both resilience and flexibility, allowing the tire to absorb shocks and maintain contact with the road. These components are meticulously bonded together using specialized adhesives, culminating in a lightweight, circular framework known as the carcass. This design not only enhances structural integrity but also ensures that the tire can withstand varying loads and pressures. Surrounding the carcass is a flat band of rubber, heat- and pressure-bonded to create the tread—the part of the tire that makes direct contact with the road. The tread is designed with specific patterns to optimize traction and improve handling in various conditions, whether it’s wet, dry, or uneven surfaces. To further enhance performance, the carcass of a radial tire is reinforced with belts made of polymer threads or steel wires, which provide additional strength and stability. These belts help distribute forces evenly across the tire, reducing the risk of deformation during operation.

Connecting the tread to the wheel is a relatively thin sidewall, which houses steel cables in the bead area that secure the tire firmly onto the wheel. This connection is crucial for maintaining the tire’s shape and performance under load. Overall, the pneumatic tire represents a remarkable blend of engineering and material science. It is a durable and cost-effective solution that enables fast, convenient, and safe personal transportation. By facilitating mobility, pneumatic tires contribute significantly to travel independence and support a vast, flexible network for overland freight delivery, shaping the way goods and people move across distances.

To enhance the structural integrity of the tire, polymer threads or steel wires are strategically integrated into the carcass, significantly boosting its durability and stability. A relatively slender sidewall connects the tread to the steel cables in the bead area, providing essential support and flexibility. These steel cables firmly clamp the tire onto the wheel, ensuring a stable and reliable connection for optimal performance.

The pneumatic tire is a resilient and cost-effective invention that facilitates fast, convenient, and safe personal transportation. Its versatility fosters complete travel independence and supports the development of a vast and adaptable network for overland freight delivery, making it a cornerstone of modern transportation systems. Pneumatic tires are utilized across a wide range of vehicles, from vehicles and trucks to earthmovers and airplanes.

These tires are crucial for vehicle performance, offering traction, braking, steering, and load support. Filled with air, they create a flexible cushion between the vehicle and the road, smoothing out shocks and enhancing ride quality for a more comfortable driving experience. This combination of functionality and comfort makes pneumatic tires an indispensable component of our daily transportation.

The Tire-Road Interfaces

Tires are among the most complex structures in automotive design, comprising various rubber compounds and combinations of rubberized fabrics or cords made from materials like steel and textiles. These reinforcement elements, known as plies, are strategically embedded in the rubber at specific orientations to enhance strength and durability. The outer surface of a tire features a carefully designed tread pattern, often referred to as the tire profile. This tread design plays a crucial role in channeling water away from the contact area during wet conditions, improving grip depending on road surfaces. It ensures optimal contact between the tire and the road, facilitating the transfer of dynamic forces essential for effective traction.

Each tire has unique structural and geometrical design parameters that influence its properties and, consequently, vehicle performance. Vehicle manufacturers set specific performance requirements that tire manufacturers must meet, which can include aspects like traction during acceleration and braking, stability while cornering, and energy efficiency (low rolling resistance) during operation.

The interface between the tire and the road, along with the forces and dynamics involved when the tire is in motion, plays a vital role in overall vehicle dynamics. Understanding these interactions is essential for optimizing tire performance and enhancing the driving experience.

One significant advantage of rubber tires is their impact on vehicle turning capabilities. Historically, vehicles could not effectively make turns at speeds above a crawl, even with the presence of differentials. Horse-drawn carts, for example, relied on the pulling force of the horses to navigate corners, often without the benefit of traditional axles. The rigid wooden or metal tires used on early horseless carriages produced only minimal lateral force, which restricted turning to very low speeds and resulted in a bone-jarring ride. In contrast, modern rubber tires provide the flexibility and traction needed for safe and efficient turns at higher speeds, greatly enhancing vehicle performance and comfort.

Tires & Load Carrying

The load-carrying capacity of tires is vital for the performance and safety of automobiles. Tires are engineered to support the vehicle’s weight, including passengers and cargo, while providing stability and traction across various surfaces. A well-designed tire evenly distributes this load, which minimizes wear and maximizes road contact for better grip. This is especially important during acceleration, braking, and cornering, where the tire must perform optimally under different conditions. Moreover, tires are built to absorb shocks and vibrations from the road, enhancing ride comfort and protecting the vehicle’s suspension system. Ultimately, the efficiency with which tires carry loads directly influences fuel economy, handling, and the longevity of both the tires and the vehicle.

It’s also important to note that the internal pressure of a pneumatic tire rises in proportion to the load it carries. The pressure within the tire’s air chamber is evenly distributed across the contact surface with the road, correlating to the total weight divided by the number of wheels. For instance, a 1,000 kg vehicle evenly distributed over four wheels would exert 250 kg on each tire. When properly inflated, the air cushion effectively supports this load, maintaining equilibrium. However, factors like heat generated from friction and the flattening of the tread can increase internal tire pressure.

On smooth roads, this pressure remains relatively stable, as the tire’s primary role is to flex the rubber in its sidewalls. While this bending leads to some energy loss, it also reduces impact forces. Despite the constant movement of air within the tire, the rapid expansion and compression during rotation largely counteract this energy loss. On rough surfaces, increased compression in air-filled tires may occur due to obstacles, but the quick expansion helps dissipate heat, balancing these effects.

When it comes to speed, pneumatic tires hold an advantage over metal ones due to the principle of least resistance. This is evident since no road is perfectly smooth; even on an ideally smooth surface, pneumatic tires outperform metal tires thanks to their lower friction.

Another factor enhancing the speed advantage of pneumatic tires is their ability to lower the roadbed grade. While this may seem minor, the layer of dust on any road surface significantly influences compression dynamics. Solid tires continuously compress this dust layer, gradually raising the grade—albeit slightly and consistently—especially noticeable at moderate speeds. In contrast, pneumatic tires compress more easily, distributing their weight over a larger area at the point of contact, which effectively lowers the grade. This phenomenon can be likened to the difference between steel and iron rails; steel requires 25% less force to support a ton of weight due to its hardness. Even if the depression of the rails isn’t visible, it is still a reality. Similarly, when navigating smooth or hard surfaces, tires tend to sink into the crevices between stones, adhering to the same principle. Theoretically, pneumatic tires are nearly perfect due to their multiple advantages. While spring wheels are considered alternatives, the ultimate solution lied in developing a puncture-proof, finely engineered air-confining fabric. Such an innovation would have solidified the supremacy of pneumatic tires, exceedingly even the most ambitious theoretical claims.

Tires & Turning

A tire is an elastic structure made of “rubber and string,” as some of the tire guys say, but that simplification is deceiving. An elastic material such as rubber yields to an external force, resists movement with an opposing force, and recovers when the external force is removed. Steel is another highly elastic material. This elastic characteristic of a tire allows the tire to be pointed in a direction different from the direction the vehicle is headed. This means the leading edge of the tread contacts the ground slightly to one side of the rest of the contact patch. As the tire rolls, each small increment of tread rubber coming onto the road sits down another small distance toward the direction the tire is pointed. As the vehicle’s weight comes onto these small increments, they stick to the road. The tread is now pulling the rest of the tire and generating forces that go through the wheel and the suspension to turn the vehicle. The force needed to change the vehicle’s path is generated by the tire and is called lateral force or side force.

To better understand vehicular turning and in turn the slip angle, we can think of a person walking along a circular path. As the person walks, he changes direction gradually, turning his foot at a small angle with each step. When the heel of his foot hits the ground, the rest of that foot follows in the new direction. As weight shifts onto this foot, it points toward the new heading, while the second foot is till pointing the older direction. This process continues with each step, causing the walker to trace an arc. Similarly, when a tire receives steering input, each small increment of tread that contacts the road also shifts slightly toward a new direction. As long as the steering input remains constant, each section of tread makes contact with the road at a slight angle, while the rest of the tire continues to align with the old direction. However, that part of the tire will eventually rotate back into contact with the road, resulting in a change of heading for both the tire and the vehicle. Additionally, as the tire rolls through the contact patch, it deforms and then recovers as the vehicle lifts off that section. The force needed to create this deformation generates the lateral force that helps change the vehicle’s path. Now, consider the rear tires. When the front tires respond to steering with a slip angle, they generate lateral forces that help steer the front of the vehicle in a new direction. If the rear tires were free to swivel, the back of the vehicle would slide outward from the turn. However, since the rear tires are fixed, they create their own slip angles and lateral forces that help stabilize the vehicle’s movement.

Typically, when a vehicle travels in a straight line, the wheel’s heading direction aligns with its travel direction, meaning that the wheel’s rotational plane and travel direction coincide. However, during lateral or “yaw motion[1],” the travel direction may deviate from this rotational plane. In forward motion, the wheel generates traction to propel the vehicle and experiences braking force during deceleration, along with constant “rolling resistance[2]”.

When a vehicle turns a corner, it follows an arc that represents a segment of a circle. The radius of this arc can change depending on the turning angle, and there are two types of turning radii: the “Curb-to-Curb Turning Radius[3]” and the “Wall-to-Wall Turning Radius[4].” At any given moment, the vehicle is following a specific arc path. To maintain this path, the vehicle must accelerate toward the “center of the arc[5]”. This requires a force, as the vehicle has mass (weight), and the tires manage these forces.

The force generated by the tires during a turn is known as “cornering force[6],” which can also be referred to as “lateral force,” “side force,” or simply “grip.” Additionally, during “cornering[7]”, the vehicle may experience “pitch[8]”, which is the forward or backward tilt of the vehicle’s body. This can occur as weight shifts from the rear tires to the front tires during braking or from the inside tires to the outside tires while turning.

The accompanying illustrations detail the various forces acting on the tires while turning and provide insights into the mechanics of cornering. Understanding these dynamics, including pitch, is essential for optimizing vehicle control and performance during maneuvers.

[1] Yaw Is the Rotation Of A Vehicle About The Vertical Axis

[2] Rolling Resistance Is The Force That Opposes The Motion Of A Rolling Tire As It Moves Along A Surface. It Is Primarily Caused By The Deformation Of The Tire As It Rolls. When A Tire Makes Contact With The Ground, It Compresses Slightly, And This Deformation Leads To Energy Loss Due To Internal Friction Within The Tire Material.

[3] Curb To Curb Turning Radius Of The Smallest Circle Around Which The Vehicle’s Tires Can Turn. This Measure Assumes A Curb Height Of 9 Inches.

[4] Wall To Wall Turning Radius Of The Smallest Circle Around Which The Vehicle’s Tires Can Turn. This Measure Takes Into Account Any Front Overhang Due To Chassis, Bumper Extensions And Or Aerial Devices.

[5] Point Around Which The Vehicle Is Turning When Navigating A Curve

[6] The Lateral Force Exerted By A Tire On The Road Surface When A Vehicle Is Turning. This Force Is Essential For Maintaining The Vehicle’s Path During A Turn

[7] Cornering Refers To The Process Of Navigating A Turn Or Bend In A Roadway.

[8] Pitch Is The Forward Or Backward Tilt Of A Vehicle’s Body As It Maneuvers Through A Turn

The accompanying illustrations detail the various forces acting on the tires while turning and provide insights into the mechanics of cornering. Understanding these dynamics, including pitch, is essential for optimizing vehicle control and performance during maneuvers.

Ref: https://www.racetechlab.com/body-slip-angle-and-tire-slip-angles/

In scenarios where the wheel experiences side slip, a force perpendicular to its rotation plane emerges, acting as a reactive force against side slip when the wheel incurs a side-slip angle. Termed as the “lateral force[1]”, this plays a crucial role in enabling the vehicle’s independent motion. When the side-slip angle is minimal, this force is similar to the cornering force. This phenomenon is similar to the lift force in fluid dynamics, acting on a body moving through a fluid at an angle of attack. Various types of wheels generate such forces when subjected to side slip. Comparing pneumatic, solid-rubber, and iron wheels at small side-slip angles, it’s evident that the magnitude of this force varies significantly based on the wheel type. Notably, the maximum force achievable with an iron wheel is less than one-third of that produced by a rubber tire wheel. Pneumatic tires, in particular, generate a substantially larger force compared to solid-rubber tires.

[1] When a vehicle turns, lateral forces come into play due to the change in direction. These forces act perpendicular to the vehicle’s path and are essential for maintaining stability and control during the turn.

For optimal vehicle maneuverability, maximizing the force generated by a wheel experiencing side slip is essential. Hence, vehicles designed for unrestricted motion are typically equipped with pneumatic tires. These tires serve not only for a smoother ride but also for enhancing vehicle handling through the availability of lateral forces.

Anatomy Of Modern Age Tires

Tire labelling provides essential information about the specifications, performance, and safety of tires. Here’s a breakdown of what you might find on a tire label:

1. Tread: Ensures High Mileage, Good Road Grip and Water Expulsion

2. Jointless Cap Plies: Enable High Speeds

3. Steel-Cord Belt Plies: Optimize Directional Stability and Rolling Resistance

4. Textile Cord Ply: Controls Internal Pressure and Maintains the Tire’s Shape

5. Inner Liner: Makes The Tire Airtight

6. Side Wall: Protects From External Damage

7. Bead Reinforcement: Promotes Directional Stability and Precise Steering Response

8. Bead Apex: Promotes Directional Stability, Steering Performance and Comfort Level

9. Bead Core: Ensures Firm Seating on The Rim

Ref: Tyre Basics Passenger Car Tyres By Continental Tires/ Copyright © 2013 Continental Reifen Deutschland GmbH/ All rights reserved. TDC 10/2013 0130 1620

Tire labelling provides essential information about the specifications, performance, and safety of tires. Here’s a breakdown of what you might find on a tire label:

A. Decoding P215/65R15 95H Label on Tire

• P: Vehicle Type: Passenger vehicle (this may also be absent; if there’s no prefix, it’s assumed to be a passenger tire)/ LT: Light Truck/ T: Temporary spare tire

• 215: Tire Width: The width of the tire in millimeters, measured from sidewall to sidewall.

• 65: Aspect Ratio: The height of the sidewall as a percentage of the tire width. In this case, the sidewall height is 65% of 215 mm.

• R: Construction Type: Radial construction (most common today)/ D: Diagonal or bias ply construction

• 15: Wheel Diameter: The diameter of the wheel (rim) in inches that the tire is designed to fit.

• 95H: Load Index and Speed Rating:

i. Load Index: Indicates the maximum weight the tire can support. For example, a load index of 95 means the tire can carry up to 690 kg.

ii. Speed Rating: Shows the maximum speed the tire can safely sustain. For example, a rating of “H” means it can handle speeds up to 210 km/h.

• Tire Ply Rating: Often indicated in letters (like C, D, or E) for light truck tires, representing the tire’s strength.

• Treadwear Grade: A numerical rating that indicates the expected tread life compared to a reference tire. A grade of 300 means it should last three times longer than the reference tire.

• Traction Grade: Indicates how well the tire stops on wet pavement, rated from AA (best) to C (worst).

• Temperature Grade: Reflects the tire’s ability to dissipate heat, rated from A (highest) to C (lowest).

B. DOT Code: This indicates that the tire meets U.S. Department of Transportation standards. The last four digits denote the week and year of manufacture (e.g., 2319 means the tire was made in the 23rd week of 2019).

C. Tire Pressure Recommendations: Specifies the recommended inflation pressure for optimal performance and safety, usually found on the tire label itself or in the vehicle’s owner manual.

D. Manufacturing Information: May include details about the tire manufacturer, model name, and country of origin.

E. Special Features: Some tires may indicate special technologies, such as run-flat capabilities, eco-friendliness, or all-season performance.

1. Manufacturer (Trademark or Logo)

2. Product Name

3. Size Designation 205 = Tire Width In Mm 55 = Height-To-Width Ratio In Percent R = Radial Construction 16 = Rim Diameter In Inches (Code)

4. 91 = Load Index/ V = Speed Index

5. Tubeless Radial Tire

6. The Sidewall Is Marked with a Circle Containing An “E” And the Number Of The Country Of Homologation. This Marking Is Followed by a Multi-Digit Homologation Number, e. g. E4 e4 (4 = Netherlands)

7. Manufacturer’s Code: Tire Factory, Tire Size and Type Date of Manufacture (Week/Year) 2013 Means The 20th Week Of 2013

8. T.W.I.: Tread Wear Indicator.

9. Country Of Manufacture

Abbreviations: DOT = U.S. Department of Transportation/ ETRTO = European Tire and Rim Technical Organization, Brussels/ ECE = Economic Commission for Europe (UN institution in Geneva)/ FMVSS = Federal Motor Vehicle Safety Standards (U.S. safety code)

All other information applies to countries outside Europe:

10. Department of Transportation (U.S.A. department which oversees tire safety standards)

11. Max. Load Rating 615 kg per wheel.

12. Tread: beneath which there are 4 plies (1 polyester ply, 2 steel belt plies, 1 polyamide ply) Sidewall: the tire casing consists of 1 polyester ply

13. U.S. limit for max. inflation pressure 51 psi (1 bar = 14.5 psi)

Information for consumers based on comparison values with standard reference tyres (standardized test procedures)

14. Treadwear: relative life expectancy of the tire based on standard U.S. testing (as % of the value for the reference tire)

15. Traction: A, B or C = wet braking capability of the tire

16. Temperature: A, B or C = temperature stability of the tire at higher test speeds. C is sufficient to meet U.S. statutory requirements

17. Identification for Brazil

18. Identification for China

Ref: Tyre Basics Passenger Car Tyres By Continental Tires/ Copyright © 2013 Continental Reifen Deutschland GmbH/ All rights reserved. TDC 10/2013 0130 1620

Traction, Braking & Safety

The first pneumatic tires had a smooth tread with no pattern. As automobile speeds increased, handling and safety issues arose, leading to the introduction of tread patterns in 1904. These patterns have since been refined with advanced tread block designs and siping techniques. Today, smooth-tread tires, known as “slicks,” are mainly used in motor racing, while public road tires must have tread patterns to channel water away and maintain road contact in wet conditions. Tread patterns, especially on winter tires, improve grip and traction. When driving at high speeds on wet roads, water can accumulate between the tire and the surface, risking aquaplaning and loss of steering control. Adequate tread depth is crucial, as worn tires can increase the risk of accidents even at lower speeds.

Tires are essential to vehicle safety and performance, yet they often receive insufficient attention. Proper tire tread is vital for safety, fuel efficiency, and overall performance. While many people consider seat belts and airbags the primary safety features, tires also play a critical role. A healthy tire ensures optimal grip on the road, reducing the risk of slipping or failing to stop when needed. Each tire is meticulously designed to maximize road safety and performance. There are few straight lines embedded on the tires which are the grooves in the tread patterns & which are designed to expel water in order to prevent hydroplaning and providing stability to the car in winter and monsoon conditions. In these grooves, you will find small shapes known as tread wear indicator. These are placed to indicate the legal wear out of your tires. If after a long usage, you find that the tire tread depth is perpendicular to the direction of the indicator, it’s time to replace your car tires.

Tyres have tread across their entire circumference. Tread depth measurements must be taken in the main grooves which feature TWIs[1] on modern tyres. In most European countries the law specifies a minimum tread depth of 1.6 mm; that’s when tyres have to be replaced. In order to ensure the tyres always offer best possible performance, summer tyres should be replaced when they reach a depth of 3 mm, and winter tyres when they reach a depth of 4 mm. Also, all four-wheel positions should be fitted with tyres of the same tread pattern design[2], and each axle, at least, should have tyres with the same tread depth. Regrooving of passenger car tyres is forbidden by law. The importance of maintaining sufficient tread depth is evident in the data: a worn tire with a tread depth of 1.6 mm can have a braking distance nearly twice as long as a new tire with approximately 8 mm of tread.

[1] TWI = Tread Wear Indicator, small raised bars across the main grooves. The bars have a height of 1.6 mm and gradually become level with the tread as the tire surface wears.

[2] One should avoid mixing summer and winter tyres in particular, which is even illegal in some European countries.

Ref: Tyre Basics Passenger Car Tyres By Continental Tires/ Copyright © 2013 Continental Reifen Deutschland GmbH/ All rights reserved. TDC 10/2013 0130 1620

Evolution of Electric Vehicles (EVs) & Their Tires

As Internal Combustion Engine Vehicles (ICEVs) are increasingly replaced by Electric Vehicles (EVs), tailpipe emissions are declining. However, EVs bring their own set of environmental challenges, particularly concerning pollution from “road-wear particles.” As tires wear down during use—especially with rapid acceleration, braking, and sharp turns—they release tiny particles into the environment. Even conservative driving contributes to this particulate pollution, and the issue is expected to worsen as more drivers switch to EVs. While EVs significantly reduce tailpipe emissions due to advanced filters and catalytic converters, tire wear presents a challenge that is not easily mitigated. Emissions Analytics reports that a single EV sheds an average of 18 kg of material annually, translating to approximately 6 million metric tons of pollution globally each year, primarily from wealthier countries with higher vehicle usage rates. EVs are typically 400-500 kg heavier than their gasoline or hybrid counterparts due to their batteries, which can weigh as much as a small car. This increased weight results in approximately 20% more tire wear. Studies indicate that Tesla’s Model Y generates 26% more particulate pollution than a comparable Kia hybrid. Additionally, the electric motors in EVs provide more aggressive torque, leading to faster acceleration and increased particulate emissions per mile compared to ICEVs. These particulates comprise a toxic mix of microplastics, volatile organic compounds, and other chemical additives that can contaminate air, soil, and waterways near roadways. Materials shed from tires settle along roads, where rain can wash them into water sources, while smaller particles linger in the air and can be inhaled. The tiniest particles, known as PM2.5, can enter the bloodstream directly. A 2017 study estimated that tire wear accounts for 5-10% of oceanic microplastic pollution and 3-7% of airborne PM2.5 pollution. One concerning tire additive, 6PPD, prevents rubber from cracking but reacts with ozone to form 6PPD-quinone, a compound linked to salmon die-offs in the Pacific Northwest. A 2022 study confirmed that this substance is harmful to various fish species and can accumulate in edible plants like lettuce. Furthermore, research in South China has detected both 6PPD and 6PPD-quinone in human urine samples, raising concerns about potential health impacts ranging from skin irritation to respiratory issues and neurological damage. As the market for EVs continues to grow, several challenges associated with tire performance and environmental impact must be addressed by manufacturers, consumers, and advocates. The weight of EVs leads to greater tire wear and a higher risk of blowouts, necessitating specialized tires that focus on durability, heat resistance, and improved tread designs. The delivery of torque in EVs also differs significantly from ICEVs; the instant torque can accelerate tire wear if tires are not engineered for such performance. Rolling resistance is another critical factor for EV tire performance. While lower rolling resistance tires can enhance an EV’s range by reducing energy consumption, achieving necessary grip and handling without sacrificing efficiency poses challenges for tire engineers.

Torque & Power Graphs Of EV & ICEV

Some may not realize but many electric vehicles or two-wheelers use EV-specific tires, that are different from normal road tires used ICEVs. While EVs and conventional vehicles share many similarities, there are crucial factors that require distinct tire designs for the two mobility formats. Here are five key differences between an EV-specific tire and regular vehicle tires.

1. Maximum Torque: One of the characteristics that set EVs apart is that they develop torque differently to a ICEVs. When an EV pulls away, its tires have to transfer all of the torque produced by its drive system to the road instantly. The increased loads and higher torque generated by an electric vehicle can increase tire wear.

2. Higher Load Capacity: EVs need tires that have been designed to handle the higher loads involved as they tend to have a different weight distribution compared to traditional ICEVs due to the placement of heavy battery packs that generally sit in the floorboard area. EV-specific tires are designed to accommodate this unique weight distribution, providing enhanced traction, stability, and handling. The tread patterns and sidewall construction are optimized to evenly distribute the vehicle’s weight and maintain consistent grip on the road surface, especially during cornering and braking maneuvers.

3. Rolling Resistance: One of the primary differences between an EV-specific tire and regular ICEV tires is their optimized rolling resistance. EV rely solely on electric power for propulsion, making energy efficiency a top priority. EV-specific tires are engineered to have minimum rolling resistance, reducing the amount of energy required to move the vehicle. These tires typically feature advanced tread patterns, specialized rubber compounds, and lower sidewall stiffness, allowing EVs to achieve maximum range and extend battery life.

4. Tire Noise: Another important consideration for EV manufacturers is minimizing cabin noise or Noise, Vibration and Harshness (NVH) levels, as EV lack the typical engine noise associated with internal combustion engines. EV-specific tires are engineered to reduce rolling noise and provide a quieter driving experience. Manufacturers employ innovative tread block designs and noise-absorbing materials to mitigate vibrations and dampen noise levels, contributing to a more comfortable and serene ride.

5. Load-Bearing Capacity/ Heavier Batteries: Most electric cars are around a third heavier than ICEVs equivalents; for instance, the EV variant of Tata Nexon, which is a midsegment car has its kerb weight ranging between 1,437 to 1,531 kg (depending upon battery capacity) while regular its ICE variant has kerb weight of only 1255 kg – which means EV model is about 20% heavier than its ICEV variant. Due to this weight of the battery packs, EV are often heavier than their conventional counterparts & hence EV specific tires are designed to handle this increased load, offering higher load-bearing capacities than ICEV tires. This ensures that the tires can safely support the higher weight of the vehicle, preventing premature wear, overheating, and other potential safety hazards.

6. Regenerative Braking Considerations: EVs commonly employ regenerative braking systems to recapture and convert kinetic energy into electrical energy, which is then stored in the battery. EV-specific tires are tailored to enhance the effectiveness of regenerative braking by offering improved grip and traction. The rubber compounds and tread patterns are optimized to provide excellent braking performance, allowing EVs to utilize regenerative braking to its fullest potential.

Labeling Of EV Tires

One of the biggest reasons why tyres for EVs differ from those for ICEVs is their weight. Battery packs are significantly heavier than traditional engines, making EVs overall heavier. This added weight is carried by the tyres, which must be specially adapted to handle the increased load. Without these modifications, tyres would wear out much faster, leading to more frequent replacements. As a result, EV tyres are built for higher load capacities and often reinforced, sometimes marked with HL (Heavy Load) designations. Tyres perform best when their tread maintains an optimal shape, relying on the correct air pressure for the weight they carry. Overloaded or under-inflated tyres can bulge, creating an improper footprint that increases tread wear. Under-inflation also decreases stiffness, compromising control, especially during cornering, and raises rolling resistance, leading to higher energy consumption. To address these issues, many EV tyres feature reinforced sidewalls and may operate at higher pressures. The sidewall, visible from the side of the vehicle, contains important markings like manufacturer details, size, and date. Reinforcing the sidewall helps maintain its shape and stiffness at the correct pressure. EV owners should pay careful attention when selecting tyres, looking beyond just size to include the load index, indicated by two or three digits (e.g., 95 or 108), which shows weight capacity, and the speed rating, represented by a letter (like ‘Y’), indicating the maximum safe speed.

Environmental & Disposal Challenges of Old Tires

Scrap tires pose significant environmental challenges due to their non-biodegradable nature and the hazardous materials they contain. When improperly disposed of, tires can accumulate in landfills or illegal dump sites, leading to extensive soil and water contamination. As they degrade, they leach harmful chemicals, including heavy metals like lead and zinc, as well as petroleum byproducts, which can infiltrate groundwater and harm aquatic ecosystems. Additionally, scrap tires create ideal breeding grounds for mosquitoes and other pests, increasing the risk of vector-borne diseases such as West Nile virus and Zika. Their ability to trap water raises public health concerns in nearby communities. When burned, scrap tires release toxic fumes and particulate matter, contributing to air quality issues and posing respiratory risks for surrounding populations. The combustion process can emit pollutants like dioxins and furans, which have serious health implications. The sheer volume of scrap tires—estimated in the billions globally—underscores the urgency of addressing this issue. Many regions suffer from inadequate recycling infrastructure, resulting in a significant percentage of tires ending up in landfills or as litter. To mitigate the environmental impact of discarded tires, sustainable practices such as recycling into crumb rubber for use in playground surfaces, asphalt, and construction materials are essential. Innovations in tire management, including improved collection systems and public awareness campaigns, can help divert tires from landfills and promote environmentally responsible disposal. Overall, tackling the challenges posed by scrap tires requires a comprehensive approach that combines effective waste management strategies, public policy, and community engagement to foster a circular economy for tire materials.

Recycling & Refurbishing Of Old & Discarded Tires

Tire recycling is a crucial aspect of managing the millions of tires discarded annually. In the United States alone, approximately 300 million tires are thrown away each year, while globally, over 1.6 billion new tires are generated, leading to around 1 billion waste tires. While in India, approximately 1.5 million tons of end-of-life tires (ELT) are generated annually. However, only about 450,000 tons of these tires are recycled by the formal sector. This significant gap highlights the need for improved tire recycling infrastructure and processes in the country. This situation presents significant environmental challenges. Effective recycling not only reduces landfill waste but also lessens the ecological footprint of tire production by reclaiming valuable materials. The tire recycling process involves several key steps. Initially, used tires are collected from various sources, including tire retailers, auto shops, and municipal collection events. Once gathered, the tires are transported to recycling facilities where they undergo sorting based on their condition and type. The next step is shredding, where tires are cut into smaller pieces, ranging from chips to fine granules. Following this, a separation process extracts valuable components: steel belts are removed using magnets, and textile fibers are extracted to ensure the rubber’s purity for further processing. Finally, the remaining rubber is ground down into crumb rubber, which is suitable for various applications. The applications of recycled tires are diverse and beneficial for both the environment and the economy. Crumb rubber can be mixed with asphalt to create more durable road surfaces that resist cracking, enhancing the longevity of infrastructure. Additionally, recycled rubber is used to create safe, shock-absorbent playground surfaces, minimizing injury risks for children. Other applications include gym mats, flooring tiles, and lightweight fill for construction projects, demonstrating the versatility of recycled tire materials. The environmental benefits of tire recycling are substantial. By recycling tires, millions can be diverted from landfills, reducing pollution and conserving natural resources. This process recovers valuable materials, decreasing the demand for virgin resources and lowering energy consumption and emissions associated with new material production. Furthermore, tires can serve as an alternative fuel source in industrial processes, replacing fossil fuels and contributing to energy recovery. However, tire recycling faces several challenges. The extensive design and complex materials used in tires make them indestructible, complicating the recycling process. Additionally, contamination from oils and chemicals poses challenges. In India, for instance, approximately 1.5 million tons of end-of-life tires (ELT) are generated annually, but only 450,000 tons are recycled by the formal sector. Moreover, the market demand for recycled rubber products can be inconsistent, impacting the economics of recycling operations. To address these challenges, innovations in recycling technologies are emerging. One notable method is pyrolysis, a thermal degradation process that treats rubber and used tires at high temperatures in the absence of oxygen. This technology breaks down tires into smaller molecular mass products, including:

1. Pyrolysis Oil: An alternative energy source that can be used as boiler fuel or for electric power generation.

2. Carbon Black: During pyrolysis (a thermal decomposition process), tires can be converted into carbon black, which is used as a reinforcing agent in new tires and other rubber products & can be utilized in various industries, including metallurgy, paint production, building materials, and the manufacture of fuel briquettes.

3. Gas: Generated during pyrolysis, this can be used to power the recycling system and contribute to electricity generation.

4. Metal Cord: Reclaimed for use in the metallurgical industry.

5. Refurbishing: Old tires can be repurposed into various by-products, contributing to sustainable practices and reducing environmental impact. Here are some common by-products derived from old tires:

• Crumb Rubber: Ground rubber from tires is used in various applications, including playground surfaces, sports fields, and rubberized asphalt for roads.

• Tire-Derived Fuel (TDF): Scrap tires can be processed into fuel for cement kilns and power plants, providing a high-energy alternative to traditional fossil fuels.

• Rubber Mulch: Shredded tires are used as mulch in landscaping and gardening, offering benefits such as weed suppression and moisture retention.

• Recycled Rubber Products: Old tires can be transformed into products like mats, floor tiles, and automotive parts, providing durable and weather-resistant materials.

• Belt and Hose Manufacturing: Recycled rubber can be used to manufacture belts, hoses, and gaskets for various industrial applications.

• Civil Engineering Applications: Tires can be used in construction projects, such as lightweight fill material for embankments or sound barriers.

• Adhesives and Sealants: Processed rubber from old tires can be incorporated into adhesives, sealants, and coatings.

By such recycling & refurbishing of old tires the environmental footprint of scrap tires can be reduced while providing valuable materials for various industries.

Epilogue: Future Of Tires

1. Airless Tires: Airless tires, also known as non-pneumatic tires (NPT) or flat-free tires, do not rely on air pressure for support. They are commonly used on small vehicles such as ride-on lawn mowers and motorized golf carts, as well as on heavy equipment in environments where punctures pose a significant risk. Closed-cell polyurethane foam tires are also available for bicycles and wheelchairs. The main advantage of airless tires is their immunity to flats, resulting in less frequent replacements. Heavy equipment equipped with these tires can handle heavier loads and perform better in rugged conditions. However, airless tires generally have higher rolling resistance and provide less suspension compared to traditional pneumatic tires. Additionally, managing heat buildup can be a challenge for airless tires used in heavy machinery. These tires are often constructed from compressed polymers or solid molded materials instead of air. While airless tires are gaining popularity, they are less favored by hardcore off-road enthusiasts, particularly at speeds exceeding 80 km/h (50 mph), where instability and vibrations can impact vehicle control and passenger comfort. Airless tire designs have evolved over the years. In 1938, J.V. Martin invented a safety tire made from hickory hoops encased in rubber, which could navigate over substantial obstacles. In 2005, Michelin introduced the “Tweel,” a tire and wheel combination designed to operate without air. Despite its advantages, the Tweel generates vibrations at high speeds, limiting its use to golf carts, ATVs, and skid steer vehicles. Michelin and GM have announced plans for a new airless tire for passenger vehicles, expected to launch in 2024. Resilient Technologies, in partnership with the University of Wisconsin–Madison, developed a “non-pneumatic tire” for the Humvee, and their Terrain armor tire became the first mass-produced airless tire after being acquired by Polaris. Bridgestone is developing the Air-Free Concept Tire, which can support up to 150 kg (330 lbs) per tire, while Hankook is working on the iFlex airless tire. Despite these advancements, many manufacturers, including Goodyear, anticipate that their airless tires will not be ready for road use until 2030 due to various limitations.

2. Orbis Wheel: The Orbis driven wheel represents an innovative advancement in tire technology, designed to enhance the performance and versatility of various vehicles, particularly electric and autonomous ones. Its unique structure improves traction, stability, and overall vehicle dynamics, making it suitable for applications such as robotics, heavy machinery, and passenger vehicles. One of the key features of Orbis driven wheels is their distinct geometry. Unlike traditional tires that rely on air pressure, Orbis wheels distribute weight evenly across their surface, enhancing grip and reducing the risk of punctures. This construction performs well in diverse terrains, from rugged off-road environments to urban settings. In terms of performance, Orbis wheels optimize energy efficiency by lowering rolling resistance. This is particularly beneficial for electric vehicles, as it extends battery life and range. The design also improves handling characteristics, giving drivers better control, especially in high-speed or challenging conditions. Furthermore, the potential for technology integration adds to the appeal of Orbis driven wheels. Equipped with sensors that monitor performance metrics like tire pressure and temperature, these wheels can facilitate proactive maintenance. In autonomous vehicles, such data enhances navigation systems and safety features, making the driving experience more reliable.

The implications extend beyond individual vehicles, as innovations like Orbis wheels contribute to greater sustainability in the automotive industry. By increasing the efficiency of electric vehicles, they help reduce environmental impact. In summary, the Orbis driven wheel merges innovative design with advanced performance capabilities, making it a promising option for the future of transportation. Its adaptability and efficiency could significantly shape a more sustainable mobility landscape, particularly as the industry moves towards electrification and autonomy.

3. REE Corner: REE corner technology offers a revolutionary perspective on vehicle design by reimagining the role of wheels in automotive engineering. Traditionally, wheels have been mere passive components, but with the REE corner concept, they become integral to the vehicle’s overall functionality. Each REE corner encompasses the wheel, electric motor, suspension, and braking systems in a compact unit, effectively transforming the wheel into a multifunctional hub. This integration not only enhances the vehicle’s performance by allowing for precise control and improved handling but also reduces weight, leading to greater energy efficiency. From a design standpoint, REE corners can accommodate various wheel sizes and types, allowing manufacturers to tailor vehicles to specific needs, whether for urban commuting or heavy-duty logistics.

Ref: REE-Investor-Presentation-May-2024.pdf

The flexibility of this modular approach means that different configurations can be quickly implemented, fostering rapid innovation and adaptation to changing market demands. Looking ahead, the evolution of REE corners could revolutionize urban mobility. By facilitating designs that allow for omnidirectional movement, vehicles could navigate tight spaces more effectively, enabling innovations like autonomous delivery drones or compact city taxis. In essence, REE corner technology redefines the wheel from a simple rotation device to a pivotal player in the future of smart, sustainable transportation.

4. Other Evolving Tire Technologies: The future of tire technology is evolving rapidly, driven by advancements aimed at improving safety, performance, sustainability, and adaptability. Here are some of the most promising new technologies for future tires:

• Smart Tires: Equipped with embedded sensors, smart tires monitor in future will be able monitor key parameters of tires such as pressure, temperature, tread depth, and wear. This real-time data can enhance vehicle safety and performance by providing insights for proactive maintenance and improving fuel efficiency.

• Self-Healing Tires: These tires will use materials that can repair minor punctures or cuts autonomously. Incorporating materials with self-healing properties, they will be able to maintain their integrity and extend their lifespan, reducing the need for frequent replacements.

• Regenerative Tires: Some tire designs are being developed to generate energy as they rotate. This technology harnesses the kinetic energy from the tire’s movement, converting it into electrical energy to power vehicle systems or charge batteries.

• Advanced Tread Designs: Future tires will feature innovative tread patterns and materials that enhance grip, especially in wet or icy conditions. Developments in tread block geometry and fine siping techniques can improve water displacement and traction.

• Sustainable Materials: The use of renewable and recycled materials is becoming a priority. Biodegradable rubbers and eco-friendly composites are being explored to reduce the environmental impact of tire production and disposal.

• Variable Pressure Tires: These tires can adjust their pressure based on the driving conditions. This technology allows for lower pressures in off-road situations for better traction and higher pressures for improved fuel efficiency on highways.

• 3D-Printed Tires: As additive manufacturing advances, 3D-printed tires may become a reality. This could allow for customized designs tailored to specific vehicle requirements and reduced waste during production.

• Enhanced Durability Technologies: Innovations in materials science are leading to stronger and more resilient tire compositions. These advancements can improve puncture resistance and overall tire longevity.

• Connected Vehicle Integration: As vehicles become more connected, future tires may communicate with vehicle systems and infrastructure, enabling features like adaptive performance based on road conditions and predictive maintenance alerts.

These emerging technologies hold the potential to transform the tire industry, enhancing performance, safety, and sustainability while adapting to the changing landscape of transportation. As these innovations are developed and implemented, they will play a crucial role in the evolution of mobility in the years to come.

Oldest Wheel: This Ljubljana Marshes Wheel with The Axle Is The Oldest Wooden Wheel Yet Discovered Dating To The Copper Age (C. 3,130 BC).

Biggest & Heaviest Wheel: Letourneau L-2350, The Most Expensive & The Largest Wheels (4.5M In Height And 4 M In Dia, weighing ~6Tons) & Costing Whopping Rs. 50 Lakhs.

About the Author

Prabhat Khare

Executive Vice President, [Lithion Power Private Limited]

Subject Matter Expert, [Manufacturing – Automotive Skill Development Council]

BE (Electrical), Gold Medalist, IIT Roorkee

Technology Article Writer, System Auditor, Trainer

Automotive & Engineering Consultant

Auto Sector Expert (Ex Tata Motors, Ex Honda Cars & Ex Ashok Leyland)

Lead Assessor for ISO 9K, 14K, 45K & 50K (BSI)

Email: prabhat.pkmail@gmail.com/ prabhatkhare22659@gmail.com, Mob: +91-9910490088

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