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CHAPTER 1 INTRODUCTION Tyres are a very important feature of a vehicle. The overall performance of your fleet may well depend on what type of tyres you fit on your vehicles. Tyre is an inseparable assembly of materials with different properties, whose manufacture demands great precision 1.1 Tyre Definition: A tyre can be defined as an envelope of rubbers and chemicals, reinforced with fabric. The tyre is held to a metal rim by the compressive forces of wire beads. The primary function of the tyre is to contain a volume of compressed air which in turn, creates the pressure sufficient to carry the load of the vehicle and move it at the desired speed. Fig 1.1Tyre functions 1

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CHAPTER 1

INTRODUCTION

Tyres are a very important feature of a vehicle. The overall performance of your fleet

may well depend on what type of tyres you fit on your vehicles. Tyre is an inseparable

assembly of materials with different properties, whose manufacture demands great precision

1.1 Tyre Definition:

A tyre can be defined as an envelope of rubbers and

chemicals, reinforced with fabric. The tyre is held to a metal

rim by the compressive forces of wire beads.

The primary function of the tyre is to contain a volume of

compressed air which in turn, creates the pressure sufficient to

carry the load of the vehicle and move it at the desired speed.

Fig 1.1Tyre functions

The major characteristics of the tyre can be summarized as follows:

Load carrying capacity

Cushioning ability

Torque transmission

Steering response

Road holding ability

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1.2 TYRE TERMINOLOGY:

The major components of a tyre are described below:

TREAD: The rubber in contact with the road.

This puts necessary pull on the tyre to make the

vehicle move.

SIDEWALL: The part of the tyre which keeps

the plies intact. It also provides some cushioning

effect by means of flexing when load is applied

on it.

Fig 1.2 Tyre terminology

PLY: The layer made up of steel and rubber that takes up the load.

INNERLINER: A layer of special rubber compound put on the inner side of the tubeless

tyres to prevent loss of air.

BEAD BUNDLE: A set of steel wires bundled together and put with the rubber to make the

tyre sit on the rim properly and seal it.

CHAFER: A layer of hard rubber that resists erosion of the bead area by the rim flange.

1.3 TYRE DIMENSION:

Tyre companies through out the world follow standard norms for tyre dimensions, tolerances,

load carrying capacities and inflation pressures for the different tyre categories and sizes.

These are decided and governed by tyre

manufacturer's association. The basic tyre

and rim nomenclature is explained below:

The basic tyre and rim nomenclature is

explained below:

OUTSIDE DIAMETER (OD): The

diameter of an unloaded tyre, mounted on

its recommended rim and inflated to

recommended pressure.

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SECTION WIDTH (SD): The width of the inflated tyre section, excluding any lettering or

decoration.

SECTION HEIGHT (SH): The radial distance between where the bead sits on the rim to the

outer most point at centerline.

STATIC LOADED RADIUS (SLR): The radial distance between the road surface to the

axle center under nominal tyre load /inflation conditions.

LOADED SECTION WIDTH: The width of the loaded cross-section.

MINIMUM DUAL SPACING: The minimum recommended distance between centerline of

dual mounted tyres to avoid the tyres rubbing against each other.

ASPECT RATIO: The ratio of section height to section width expressed in percentage.

There's a lot of useful information molded into the sidewall of a tyre. It shows the name of

the tyre, its size, whether it is tubeless or tube type, the tyre grade, speed rating, the maximum

load, maximum inflation, an important safety warning and more.

Passenger Tyre Sidewall Information :

1. BIAS:

5.90 15INFLATED SECTION WIDTH (INCHES) NOMINAL BEAD DIA (INCHES)

2. Radial:

P 215 65 R 15 89 HPassenger

CarSection width

Aspect Ratio Radial Rim

DiameterLoad Index

Speed Rating

"P" means this is a passenger car tyre (as opposed to a tyre made for a truck or other vehicle).

P- metric is the U.S. version of a metric tyre-sizing system.

"215" Section Width: The width of the tyre in millimeters from sidewall to sidewall. This

measurement varies depending on the width of the rim to which the tyre is fitted: larger on a

wider rim, smaller on a narrow rim. The number on the side of tyre indicates the width

measured with the tyre fitted to the recommended rim width.

"65" Aspect Ratio: The ratio of height to width; this tyre's height is 65% of its width.

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"R" Construction: How the plies are constructed in the tyre carcass. "R" means radial. "B" in

place of the "R" means the tyre is belted bias construction. "D" in place of the "R" means

diagonal bias construction.

15" Rim Diameter: The diameter of the wheel in inches.

"89" Load Index: This tyre has an industry-standard maximum load of 580 kilogram.

Different numbers correspond to different maximum loads. The maximum load is shown in

lbs. (pounds) and in kg (kilograms), and maximum pressure in PSI (pounds per square inch)

and in kPa (kilopascals). Kilograms and kilopascals are metric units of measurement.

"H" Speed Rating: This tyre has an industry-standard maximum service speed of 210 km per

hour. tyres using an older European system carry the speed rating in the size description:

215/65HR15. Different letters correspond to different maximum service speeds.

The letters "DOT" certify compliance with all applicable safety standards established by the

U.S. Department of Transportation (DOT). Adjacent to this is a tyre identification or serial

number; a combination of numbers and letters with up to 11 digits.

The sidewall also shows the type of cord and number of plies in the sidewall and under the

tread.

CHAPTER 2

TYPES OF TYRES

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Tyres are mainly of two types.

1).radial tyres.

2).bias tyres.

2.1 Radial and Bias Tire Construction:

There are two basic types of tire construction — radial and bias — that must be considered

when choosing either a replacement tire for certain applications or when spec’ing new tires

on an original equipment vehicle Bias ply tires are constructed of overlapping crossed layers

of cord material and are typically made with nylon, polyester, or other materials. The crossed

plies run on a diagonal from tire bead to tire bead and comprise a generally stiff sidewall

area. Sometimes, extra crossed plies or breakers are used under the tread area to further

stiffen the crown area and provide better wear resistance or other performance parameters

(such as puncture resistance, etc.). Radial ply tires are made with the cord material running in

a radial or direct line from bead (at 90 degrees to the centerline of the tire), and are typically

made with one steel body ply or multiple body plies of other materials. Under the tread area,

the radial tire usually has three or four crossed plies or belts made of steel cord to stabilize the

crown area and offer better puncture resistance. The radial sidewall area is generally less stiff

than the bias ply sidewall, though the tread area is normally much stiffer. Bias ply tires have

been designed over the years to perform in many different types of applications from all-

highway to on-off road, to all off-road service conditions. With the advent of the radial tire

and some of its inherent advantages, the bias tire is now used much less frequently in long

haul over-the-road applications. Radial tires typically are used in applications where heat

build-up with bias ply tires is a problem. With the many improvements to radial tire

construction made in recent years, the radial tire is now used in virtually all types of service

conditions.

2.2 Bias Tire Considerations:

• stiffer sidewalls give better driver

handling/feel

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• lower susceptibility to sidewall

snags/hazards/rusting

• lower initial tire purchase price.

2.3 Radial Tire Considerations:

• better treadwear performance

• higher potential for retreading

• more fuel efficient

• lower susceptibility to tread

punctures

• better traction characteristics

CHAPTER 3

FUNCTIONS OF A TYRE

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Functions of a tyre:

The major functions performed by a tyre are as follows

Steering

Carrying

Cushning

Rolling

Transmitting drive

Lasting

3.1 Steering:

The tyre should steer the vehicle with precision, irrespective of the state of the surface

and/ or climatic conditions. The stability of a vehicle's path depends on the tyre's holding

their course. A tyre must stand up to transversal forces without drifting from it's path. In

general each vehicle has a particular inflation pressure per axle. Respecting pressure

variations between front and rear ensures ideal directional stability.

3.2 Carrying:

Tyres support a vehicle not only when it is moving, but also when it is standing and

they must be able to resist considerable load transfers during acceleration and braking. A car

tyre carries more than 50 times it's weight.

3.3 Cushning:

Tyres absorb the shocks due to obstacles and cushions the vehicle from other

irregularities in the road, ensuring driver and passenger comfort as well as contributing to the

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lifestyle of the vehicle. The main characteristic of a tyre is it's great suppleness, particularly

vertically. The great elasticity of the air contained enables it to take deformation inflicted on

it by obstacles and surface roughness. The correct tyre pressure, then, gives good level of

comfort whilst retaining good steering capacity.

3.4 Rolling:Tyres roll more evenly, more surely, with less rolling resistance for greater driving

pleasure and better fuel consumption.

3.5 Transmitting drive:Tyres transmit drive: the engine's usable power, braking effort. The quality of the few

square inches in contact with the ground dictates the level of transmission of drive etc.

3.6 Lasting:Tyres last. That is, keep their optimum performance level for millions of wheel

revolutions.

The wear on a tyre is of course dependent on its conditions of use such as: -

Load

Speed

State of road surface

State of vehicle

Driving style

and to a large extent: -

The quality of its contact with the ground

Pressure therefore has a major role to play and acts upon

The size and shape of the contact patch

The distribution of stresses on the different points of the tyre in contact with the

ground.

A tyre needs air to work and last. It is vital to check tyre pressure regularly. In fact, a tyre

loses its precious air, molecule by molecule, because of the natural (very slight) porosity of

rubber. To this are often added accidental causes such as valves or rims no longer being

completely airtight, small perforations in a tyre etc. Pressure dictates all a tyre's functions:

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Incorrect pressure erodes functions such as, functions of safety, economy and comfort. A

quick, regular check will greatly reduce this area of concern for the driver. These above

functions guarantee safety, comfort and economy. They are provided during the entire

lifetime of a tyre, but elementary precautions for use must be taken by the user.

3.7 Reasons for tyre failure:Any tire, no matter how well constructed, may fail in use as a result of punctures,

impact damage, improper inflation, overloading, or other conditions resulting from use or

misuse.

Tire failure may create a risk of property damage, serious personal injury or death.

Driving on tires with improper inflation pressure is dangerous.

• Under-inflation causes excessive tire heat build-up and

internal structural damage.

• Over-inflation makes it more likely for tires to be cut,

punctured, or broken by sudden impact.

Therefore, from a logistics point of view, the tread is very important. Depending on

where the vehicle is going to be used, the tread will vary.

CHAPTER 4

RETREADING

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4.1 Retreading:

Tyre Retreading is a technology, where the old tyres are made serviceable by

removing worn out and damaged treads (rubber belts) and replacing it with new treads.

Similar to the new tyres, the treadsed tyres can be very well used on all vehicles, irrespective

of light or heavy vehicles.

4.2 Why Retread?

Retread tyres are proven to be as safe and durable as compared to new tyres. Many truck

fleets plan their new tyre purchases with the intention of having worn casings retreaded two

or more times as a routine part of their tyres’ budget.

It would cost less as compared to producing new tyres (up to 30%-50% lower).

The aircraft industry (military and commercial) saves 80 million a year.

It’s completely safe. All commercial airlines, as well as military jet aircrafts, uses

retread tyres. Approximately 80% of all aircraft tyres now in service in the US are

retreads. In 1993, on the Boeing 727 aircraft alone, 28,000 retreads were used, with an

average of 200 take-offs and landings per tread life.

Retread tyres are proven to be as safe and durable as compared to new tyres.

Professional retreaders adhere to stringent industry standards at every step of the

retreading process.

Many truck fleets plan their new tyre purchases with the intention of having worn

casings retreaded two or more times as a routine part of their tyres’ budget.

It conserves oil. The synthetic rubber components in a new passenger tyre contain 7 to

8 gallons of oil. Retreading the same tyre uses only 2 to 3 gallons of oil! The

manufacture of new medium truck tyres require 22 gallons of oil, but only 7 gallons

are required to retread.

4.3 Types of Retreading:

Retreading can be done by the following two processes:

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(1) Conventional Process (also known as 'mould cure' or 'hot cure' process) - The mould

cure system of retreading, put simply, involves the following process .used tyres are

inspected and subjected to any necessary repairs before being buffed to remove the

old tread and sidewall rubber. Uncured rubber is then applied to the tread and

sidewalls following which the tyre is cured in a mould in roughly the same way that a

new tyre is manufactured. Mould cure retreads tend to be made by larger retreaders

due to the large investment needed in moulds and would normally carry the retreaders

own brand name.

Due to its durability, the Hot Process is mainly used for Off-the-Road use (Mines and

rugged areas)

(2) Precure Process ( also known as 'cold cure')- With the precured retreading system, the

buffing process is followed by the application of a precured tread strip or ring to the tread

area of the casing. The tyre is then cured at lower temperatures in an autoclave or an

electric chamber. The Cold Process is mainly used for On-the-Road to deliver high mileage.

CHAPTER 5

PROCESS FLOW CHART

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5.1 PRIMARY INSPECTION:

The purpose of initial inspection is to verify that a casing is acceptable for retreading

using a thorough inspection of each tyre, inside and outside. Identify casing injuries and

determine if repairable. Reject or approve the casing for processing.this inspection may be

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PRIMARY INSPECTION

BUFFING

RASPING

REPAIR SECTION

COATING SECTION

APPLICATION OF RUBBER

POST CURE INSPECTION

PRE DELIVERY INSPECTION

TRIMMING AND PAINTING

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carried out by using various non-destructive sophisticated inspection equipment available in

the retread industry or with naked eye.

5.2 BUFFING:

Fig 5.1 Buffing machine

After inspection, tires have the old tread mechanically removed on

high speed buffers. The primary objective of buffing is to prepare the worn tread surface of

the tyre to receive a retread. The original tread design and some of the under tread is removed

to provide casing with the required dimensions and surface texture.

5.3 RASPING:

After the buffing is done the tyre is sent to the rasping section, where the deep cuts,

bulging spots, nail holes and nylon ply worn outs etc., will be rectified by rasping.

5.4 REPAIR:

In repair section, all the holes will be covered by cushion gum. over and above half

inch cuts will be covered by chemical patches.

5.5 COATING:

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From the repair section then the tyre goes to the coating section. Here the rasped area

of the tyre is cleaned solvent oil and then the vulcanising solution will be sprayed on the

buffed portion.

5.6 APPLICATION OF NEW RUBBER:

a) In the pre cure system, the tread rubber has already been vulcanized with the new

tread design. The buffed tire has a thin layer of cushion gum wrapped around the tread

area and the pre cured tread is then applied. The cushion gum serves to bond the pre

cured tread to the tire. The tire is then placed in a curing chamber and the pre cured

tread becomes adhered to the tire through a vulcanizing process very similar to that

used in new tire construction.

b) In the mold cure system, unvulcanized tread rubber is applied to the buffed tire. The

tire is then placed into a rigid mold which contains the tread design in the tread area.

The mold is heated and the rubber in the tread area vulcanizes and adheres to the tire

with the new tread design molded in. Again, this vulcanization process is very similar

to that used in new tire construction. Note: Both systems require a combination of

time, heat and pressure to create the vulcanization of the new rubber to the tread area

of the tire.

5.7 POST CURE INSPECTION:

After taking out the tyres from moulds/bonders post cure inspection is carried

out. Some retreaders are also using instrumented inspection like X-ray, shearographie

or high pressure tester. Unacceptable tyres are rejected and scrapped.

5.8 PREDELIVERY INSPECTION:

To insure a quality retread each tire passes thorough inside and outside visual

inspection. It is mandatory that the tire meets all customer and government regulations. This

inspection insures that only tires that meet industry quality standards are allowed to leave the

retread plant.

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5.9 TRIMMING AND PAINTING:

The retreaded tire that successfully has passed the final inspection is trimmed to

remove any excess rubber and painted. It is then ready to return to full service and a second

(or third) life as a safe and economical alternative to high priced new tires.

This is the process of retreading a tire.

CHAPTER 6

TREAD PATTERNS

Also called tire tread designs, tire tread patterns are the arrangement of continuous

ribs, independent tread blocks, circumferential and lateral grooves, as well as the thin sipes

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molded into the tread to fine-tune noise, handling, traction and wear. Tire treads patterns

feature different basic designs to help them meet anticipated driving conditions.

6.1 Symmetric Tread Patterns:

Fig 6.1Symmetric tread pattern

A symmetric tread pattern is the most common and features continuous ribs or independent

tread blocks across the entire tread face where both inboard and outboard halves feature the

same pattern. Tires featuring symmetric tread patterns allow using multiple tire rotation

patterns.

6.2 Asymmetric Tread Patterns:

An asymmetric pattern is designed to blend the requirements of dry grip and water

dispersal/snow traction where the tread pattern changes across the face of the tire. An

asymmetric tread pattern usually incorporates larger tread ribs/blocks on the outboard side to

increase cornering stability on dry roads by offering greater contact area. This also helps to

reduce tread squirm and heat buildup on the outside shoulder. The inboard side usually

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Fig 6.2 Asymmetric Tread Patterns

features smaller independent tread blocks to aid wet and/or winter traction when driving

straight ahead. Tires featuring asymmetric tread patterns allow using multiple tire rotation

patterns.

6.3 Directional (Unidirectional) Tread Patterns:

6.4 Directional (Unidirectional) Tread Patterns

A directional (also called a unidirectional) tread pattern is designed to roll in only one

direction. It incorporates lateral grooves on both sides of the tire’s centerline that point in the

same direction and result in v-shaped tread blocks. These grooves enhance hydroplaning

resistance at high speeds by pumping water more efficiently through the tread pattern. Unless

they are dismounted and remounted on their wheels to accommodate use on the other side of

the vehicle, directional tires are to be used on one side of the vehicle and are intended to be

rotated from the front axle to the rear axle. If different tire sizes are used on the front vs. rear

axle, the tires become location-specific and prohibit tire rotation unless remounted.

6.4 Asymmetric and Directional Tread Patterns:

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Fig 6.4 Asymmetric and Directional Tread Patterns

Asymmetric and directional tread patterns have v-shaped tread grooves that are offset

compared to the centerline of the tire. Tires featuring asymmetric and directional tread

patterns must be treated as directional tires for tire rotation. However, if different tire sizes

are used on the front vs. rear axle, they become location-specific and prohibit any tire rotation

possibilities.

6.6 There are 5 primary functions of the tread design.

(1) Providing grip in both wet and dry conditions.

(2) Improving driving stability.

(3) Preventing or reducing aquaplaning.

(4) Assuring adequate wear and irregular wear resistance and

(5) Having an attractive appearance.

The tread design changes. Some factors to consider when a user requests for tyres

are:

The terrain.

The road surface in project area.

The weather in the specific area.

Weight/load.

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Tires are used under many various conditions and are required to perform well in all of them.

There are currently many types of tires and they can be basically classified into three

categories.

General Standard Tire.

UHP tire(Ultra High Performance).

Winter tire.

6.6 STANDARD TIRE :

This category of tire has well balanced basic performance

Fig 6.5 standard tyre

6.7 UHP TIRE:

This category is designed mainly for high-performance cars and thus it is important perform

well providing driving stability on wet and dry roads.

Fig 6.6 uhp tyre

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6.8 WINTER TIRE:

These tires are used on winter roads and thus it is important perform well on snow and ice

surfaces.

Fig 6.7 winter tyre

A tire is constructed of many types of rubber and cords. Moreover, each tire type has

many differences in design factors such as pattern, construction and material.The

difference in design factors which have a major influence on the characteristics of each type

of tire is explained.

1. Tread Rubber

2. Tread Pattern

3. Tire Construction

1. Tread Rubber

  STANDARD UHP STUDLESS

Hardness Criterion Softer More Soft

Heat

Generation

Criterion Higher Higher

Wear

Resistance

Criterion worse worse

Hysteresis

Loss*

Criterion Higher Higher

Table 6.1 Propertiesof different types of tyres

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HYSTERESIS LOSS: When rubber is repeatedly deforming and recovering, it has some

difference between providing and giving back energy. Generally, this is called 'Hysteresis Loss'.

In the case of UHP tires, softer and higher heat generating tread rubber is necessary to

provide improved grip on dry and wet surfaces. In case of STANDARD tires, better wear

resistance and low hysteresis loss is for longer wear life and low fuel consumption. In case of

studless, the tread rubber is softer than UHP. But the purpose of using softer rubber is

different from UHP. It is to provide a better grip on ice surfaces.

2. Tread Pattern

  STANDARD UHP STUDLESS  

Void Ratio Criterion Smaller Slightly

Smaller

Uni-

directional

Not Apply Mostly

Apply

Sometime

Apply

Block Size Criterion Bigger Slightly Bigger

Sipe Density Criterion less More

Table 6.2 Tread patterns for types of tyres

In case of UHP, uni-directional patterns are mostly applied since this design provides better

water drainage. This allows for improved wet performance without making the void ratio big

(this provides a larger contact area). Smaller void ratio is better for dry grip.In case of

studless, the pattern with many sipes is designed for obtaining better traction on ice surfaces.

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3. Tire Construction

  STANDARD UHP STUDLESS

Side Stiffness

*1

Criterion Stiffer Equivalent

Tread Radius Criterion Larger Equivalent or Slightly Larger

Cap Ply Basically Not Apply*2 Mostly Apply Not Apply

Tread Depth Criterion Shallower Deeper

Belt Width Criterion Wider Equivalent

Table 6.3 Tread patterns for types of tyres

*1 In this time, stiffer side means designing high turn up ply and/or bead filler.

*2 Sometimes it applies as occasional demands.

In case of UHP, a stiffer sidewall is designed to provide for better handling stability. The

wider belt and cap ply is for high speed durability.

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The following are the basic design factors of a tread pattern, and their related performance characteristics.

These are the basic design factors of a tread pattern and their relative performance characteristics.

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CONCLUSION:

The mini project helped us a lot in knowing all about tyres and their process of

retreading.we have got to know about the tyre terminolgy,dimentions and its

designation.various functions of a tyre are known.we have got an insight on the types of tread

patterns and process of retreading. we have got an insight on the process flow chart of

retreading a tyre from the point of inspection to its end of delivery.

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