Tyres

Introduction

Functions

• Only contact with ground

• Act as the primary suspension, cushioning the vehicle from effects of rough surface.

• Provide frictional contact with the road surface which allows the driving wheels to move the vehicle

• Front tyres allows the wheels to steer

• Tyres allow braking to slow or stop the vehicle

Properties of tyres

• Non-skidding

• Uniform wear

• Load-carrying capacity

• Speed Capacity

• Cushioning

• Power consumption

• Noise

• Balance

Terminology • Steel Wheels – Most popular design. Very strong and cheap to produce.

• Alloy Wheels – Attractive and light weight, but expensive and difficult to clean.

• Spoked Wheels – Used on older vehicles. Cannot be fitted with tubeless tyres.

• Divided rims – Rims are made in two halves which are bolted together, (rims must never be separated while the tyre is inflated)

• Split rims –Tyre is held in place by a large circlip

• Plies – Layers of strong fabric which are built up to give the tyre its strength and shape

• Bead – loops of steel which are the anchor point for the plies

• Cross Ply Tyre – Main plies of the tyre run at an angle (45 degrees) from one bead to the other

• Radial Ply Tyre – Main plies of the tyre run at 90 degrees from one bead to the other

• Tread – Rubber pattern. Provides grip with the road surface and assists in clearing water away

• Side Wall – Connects the beads to the tread of the tyre

Parts

• Beads: Two rings that are made of steel wire and encased in rubber. They hold tire side walls snugly against the rim and prevent tyre from coming off

• Body Plies: Rubberized fabric and cords wrapped around beads. Form carcass or body of the tyre.

• Tread: Outer surface of the tyre that comes in contact with the road

• Sidewall: Outer part of the tyre that extends from the bead to the tread. • Marking on the sidewall provides the information about the tyre.

• Liner: Thin layer of rubber that is bonded to the inside of the plies. Provides a leak proof membrane for tubeless tires.

• Belts: Used to strengthen the body plies and stiffen the tread. • Lie between tread and plies

Parts

Carbon black adds strength and abrasion resistance, while protecting rubber against UV light. During curing, sulphur links rubber molecules together, adding strength, and giving the rubber resistance to both heat and cold. Zinc stearate Small amounts of zinc stearate and waxes help control curing rate, prevent oxidation and make rubber easier to process. Accelerators are used to control the cure rate, so different types of rubber can cure fully – in same amount of time. Antioxidants and antiozonants are added to rubber to fight degradation by oxygen and ozone, which can shorten the life of tyres.

C

O

M

P

O

U

N

D

S

Tyre Cutaway

Bias Ply Tyre Construction

• One of the oldest design

• Several textile plies are laid across

each other, running from bead to

bead in alternate directions

• Number of plies depends on the size

of the tyre and the load it has to

carry

• Same number of plies is used on the

crown and the sidewalls

• Plies run at an angle from bead to

bead

• Does not use belts

• Allows body of the tyre to flex easily

• Improved cushioning, hence smooth

ride on rough roads

• Weakness: Reduced traction at high

speeds and increase rolling

resistance

Belted Bias Tyre Construction • Bias ply tyres with belts added to increase tread stiffness.

• Belts do not run around the sidewalls, they lay under the tread area

only

• Belts and plies run at different angles

• Offers some reduction in rolling resistance over a bias ply tire

• Provides smooth ride and good traction

Radial Ply Tyre Construction

• Plies run straight across from bead to

bead.

• Has a very flexible sidewall and a stiff

tread, giving it a very stable footprint

• Consist of a carcass ply formed by

textile arcs running from one bead to

the other.

• Each ply is laid at an angle of 90

degrees to the direction the tyre rolling

• At the top of the tyre crown (under the

tread), a belt made up of several plies

reinforced with metal wire is laid.

• These crown plies, laid one on top of

the other, overlap at an angle

determined by the type of the tyre.

Advantages of Radial Ply Tyres

• Side walls can bend easily, its shock absorbing capacity is 25% more than bias ply or cross ply.

• Lower rolling resistance and hysteresis loss leads to less fuel consumption

• Longer tread life because of less heat build in tyre.

• Breaking efficiency on wet roads is better because of greater sidewall flexibility and tread stiffness.

• Better steering characteristics.

• While taking turns it has less tendency to distort and lift off the road from one side.

• Larger resistance to punctures ,cuts and impacts in the tread area.

Bias contact patch Radial contact patch

Non-Directional Tyres Uniform grooves Can run in any direction

Unidirectional Tyres Grooves are in one direction Direction of rotation is clearly marked

Cross-section of tubeless tyre

Advantages of tubeless tyres

• Lesser unsprung weight.

• Better cooling

• Lesser rolling resistance

• Comfortable ride

• Slower leakage of air

• Simpler assembly

• Improved safety

Tyre Sidewall Markings

Speed Rating

Load Rating Load

Index

Load

(Kilograms)

Load

Index

Load

(Kilograms)

71 345 91 615

72 355 92 630

73 365 93 650

74 375 94 670

75 387 95 690

76 400 96 710

77 412 97 730

78 425 98 750

79 437 99 775

80 450 100 800

81 462 101 825

82 475 102 850

83 487 103 875

Tread Patterns

Competition

Snow tyres

Feathering • Improper alignment (TOE). • Worn or damaged steering/ suspension parts. • Hard cornering

Cupping •Worn or damaged steering or suspension parts. •Improper balancing.

One Edge •Improper alignment (CAMBER). •Worn or damaged steering or suspension parts

Tyre problems

Mechanical Irregularities

Mechanical Irregularities

Camber

Right side tyre

Tread Wear Markings

Tread wear indicator

Wear Measuring tool Coin method

Nitrogen in Tyres

• Makes up around 80 percent of the air

• Dry inert gas. It is less reactive than oxygen.

• Leaks out of the sidewall three times slower then oxygen.

• Oxygen oxidizes the rubber in the sidewall.

• Pumped into tyres in a pure form, hence it does not contain moisture found in compressed ambient air which causes rusting of steel rims.

• The result is that all materials that come into contact with the compressed gas inside the tyre are less subject to oxidation corrosion

Special Service Tyre

• Space-saver spare tyre • Used to replace flat tyre • Not used for tyre rotation • Uses a special wheel • Speed and pressure restrictions

apply • It has no hub caps or wheel

covers

• Tread depth must be not less than 1.6mm over the central three-quarters of the tyre and must go all the way round the circumference in an continuous unbroken band with no bald patches anywhere on the tyre tread.

• If radial and cross ply tyres are fitted to the same vehicle, radial-ply tyres must be fitted on the rear.

• Cross-ply and radial ply tyres must never be fitted on the same axle.

• Tyre pressures must be set to the manufactures recommendations

• The tread and side wall must be free from large cuts, abrasions or bubbles

Tyre care essentials

Changing Tyre Size

• Substitute should have equal or greater load-carrying capacity

– Diameter of tyre increases load capacity

– Lower profile tyre: Wider tyre and larger diameter wheel

– Overall diameter of replacement tyre must be positive (less than 5% of original tyre)

• Tyre diameter changed: speedometer must be recalibrated

Plus size maintains same diameter by using larger wheel and lower profile

Wheel - Basics

Pilot bore fits to the hub.

• Most standard wheels are made of steel.

• Some vehicles are fitted with alloy wheels that are made of magnesium or aluminum

• The rim holds the tyre. • Well of the wheel allows the tyre to

be removed and refitted • Centre section is welded to the rim

Centre mounting section

Rim

Wheel - Basics

Two-piece Split Side rings

Three-piece Flange or Continuous rings If any components are damaged the rim must be replaced

Valve Stems and Cores

Functions – Retains air, allows inflation and deflation.

Rubber stem of the valve is pulled into the wheel.

Valve core contains a spring loaded air valve insert.

The valve core also has a sealing washer and a seat washer.

Valve cap keeps out dust and helps keep air in.

Valve caps

Sealing washer

Seat washer

Valve stem Valve core

Tyre pressures must only be checked and adjusted when the tyre is cold

Wheel studs usually have a right-hand thread.

If it is a left-hand thread, it can be marked with “L”.

Metric threads are marked with “M” or METRIC.

Wheel studs press through the hub or axle flange.

Taper on the wheel nuts secures and centers the wheel.

Wheel Fixings

Wheel studs and nuts attach the wheel to the hub.

Taper

Hub flange

Wheel mounting

Torque wrench

Wheel Nut Torque

Correct torque of wheel fixing is vital for all vehicles, and nearly all require the use of a torque wrench.

Excessive torque can lead to wheel or hub distortion, causing runout and vibration.

Low torque may allow wheel nuts to work loose and wheels to come off.

Nuts should always be tightened in a diagonal pattern.

Wheel Rim Size

Run Flat Tires

• Temporarily supports weight of vehicle even with no air pressure

• Internal support, thicker and stiffer side walls, stronger beads.

• Can maintain Mobility for upto 100 km at slow speed (60 kmph)

• Direction or speed change relies on friction between the tyres and the road surface.

• Grooves of a rubber tyre are designed to disperse water from under the tyre, providing high friction even in wet conditions.

• Aquaplaning occurs when a tyre encounters more water than it can dissipate

• Steering appears light as if we are driving with wheels in air • Water pressure in front of the wheel makes a wedge of water under the

leading edge of the tyre, causing it to lift from the road. • This loss of traction causes the wheels to slip and prevents the vehicle

from responding to steering, braking or accelerating. As a result, the vehicle can go out of control, start to skid or spin.

• Risk of aquaplaning increases with the depth of standing water • If multiple tyres aquaplane, the vehicle loses directional control and slide

until it either collides with an obstacle, or slows down so that friction is regained.

Aquaplaning (Hydroplaning)

• Tyre tread wear: Worn tyres will aquaplane more easily due to lack of tread depth.

• Tyre inflation pressure: Under inflation enhances aquaplaning • Tyre tread aspect ratio: Longer and thinner the contact patch, less likely

a tyre is of aquaplaning. (Small diameter and wide tyres are more prone to aquaplaning)

• Vehicle weight: More weight on a properly inflated tyre increases the contact patch. Weight can have the opposite effect if the tyre is underinflated.

• Vehicle type: Combination vehicles like semi-trailers are more likely to experience uneven aquaplaning caused by uneven weight distribution

SOLUTION: If aquaplaning is encountered (steering feels disconnected), DO NOT brake, accelerate, or steer the vehicle. Allow the speed to reduce on its own

Aquaplaning (Hydroplaning)

Aquaplaning (Hydroplaning)