• 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
• 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
• 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
• 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
• 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
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.
Small amounts of zinc stearate and waxes help control
curing rate, prevent oxidation and make rubber easier
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.
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
• Same number of plies is used on the
crown and the sidewalls
• Plies run at an angle from bead to
• 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
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
• 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
• 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
• 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
• 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.
• Improper alignment (TOE).
• Worn or damaged steering/ suspension
• Hard cornering
•Worn or damaged steering or
•Improper alignment (CAMBER).
•Worn or damaged steering or
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
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
• It has no hub caps or wheel
• 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
• Tyre pressures must be set to the manufactures recommendations
• The tread and side wall must be free from large cuts, abrasions or
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
• Some vehicles are fitted with alloy
wheels that are made of magnesium
• 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
Two-piece Split Side rings
Three-piece Flange or
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
The valve core also has a sealing
washer and a seat washer.
Valve cap keeps out dust
and helps keep air in.
Valve stemValve core
Tyre pressures must only be checked
and adjusted when the tyre is cold
Wheel studs usually have a right-hand
If it is a left-hand thread, it can be
marked with “L”.
Metric threads are marked with “M” or
Wheel studs press through the
hub or axle flange.
Taper on the wheel nuts secures
and centers the wheel.
Wheel studs and nuts attach the
wheel to the hub.
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
Low torque may allow wheel nuts to
work loose and wheels to come off.
Nuts should always be tightened in a
Run Flat Tires
• Temporarily supports
weight of vehicle even
with no air pressure
• Internal support, thicker
and stiffer side walls,
• Can maintain Mobility
for upto 100 km at slow
speed (60 kmph)
• Direction or speed change relies on friction between the tyres and the
• 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
• 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
• Tyre tread wear: Worn tyres will aquaplane more easily due to lack of
• 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
• Vehicle type: Combination vehicles like semi-trailers are more likely to
experience uneven aquaplaning caused by uneven weight distribution
If aquaplaning is encountered (steering feels disconnected), DO NOT
brake, accelerate, or steer the vehicle. Allow the speed to reduce on its