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| All you need to know about your tyres - but never dared to ask! |
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Car Tyre Construction
Most vehicles on our roads today
are equipped with radial ply tyres, which have up to 30 individual
components each with specific functions. The materials used include
Natural and Synthetic rubber polymers, Aromatic Oil, Carbon Black,
Silica, Steel cord and Fabric cords. The illustration below shows the
main components in a modern day car tyre.
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- Tread - synthetic/ natural Rubber blend
- Cap Ply - Nylon
- Reinforcing Belts - Steel Cord
- Radial Body Ply - Textile Cord
- Inner Liner - Butyl Rubber
- Sidewall - Rubber Veneer
- Apex - Hard Rubber
- Bead Wires - Steel Hoops
- Bead Reinforcement - Textile
- Rim Strip - Abrasion resistant Rubber
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Main Components | Component | Function | | Tread Rubber | Transmits
traction, cornering and braking forces tothe road surface and provides
an abrasion resistant barrier between the main casing and the road
surface. | | Breakers/Belt Assembly | Provides support and stabilises the tread area so that the forces referred to above can be transmitted efficiently. | | Nylon Cap Ply | Consolidates the steel belt assembly, which enhances high speed durability by helping maintain dimensional stability. | | Radial Body Ply | Reinforcement
to withstand inflation pressure and provide a means to transmit forces
between the tread and the bead. Stabilises the tyre's dimensions. | | Inner Liner | Provides an airtight barrier between the inflation pressure and the tyre's internal structure. | | Sidewall Rubber Veneer | Protects the main Body Ply from physical damage and atmospheric degradation. | | Bead Filler | Provides additional support to the lower sidewall / bead area. | | Bead Wire Bundle | High
tensile steel hoops to anchor the Body Ply(s) and other components that
turn around the bead. Provides an inextendable lock onto the wheel. | | Bead Apex | Shapes
the lower sidewall to allow a gradual tapering of modulus from the bead
to the sidewall. Prevents a concentration of stresses at a single point. | | Bead Rim Strip | An abrasion resistant material wrapped around the bead to resist abrasion damage between the tyre and the wheel rim. |
The Tyre's Main Functions Figure 1
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It is the air within the tyre, which carries the load, not the tyre
itself. Air inflation is to a tyre what petrol or diesel is to an
engine, it is its fuel. Half fill the petrol tank in a car and it will
only travel half the distance it would with a full tank the same
principle applies to air inflation and tyres. The less air you put
inside the tyre, the less mileage it will achieve. Additional
under-inflated tyres will cause the car to use more fuel and compromise
vehicle safety.
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Figure 2
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The tyre is the only contact the vehicle has with the road, hence it
has to transmit both traction and braking forces to the road surface. A
remarkable feat when you consider the area of contact with the road,
for each tyre is about the size of the sole of a size 8 shoe.
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Figure 3
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When a car encounters a corner, centrifugal force tries to throw the
vehicle off line. The tyres collectively have to generate an equa force
to counteract the centrifugal force and hence keep the vehicle on its
steered path. Even when travelling in a straight line, it is the tyres,
which enable the vehicle to keep on its steered direction.
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Figure 4
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An inflation tyre and wheel unit bounces when dropped, indicating it
is a spring. The tyre has to supplement the vehicle's suspension to
provide passenger comfort.
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The Tyre's Supplementary Functions: The tyre has to perform many functions and listed below are some of them:
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The tyre has to: - be compatible with different suspension systems
- give quick response to steering response
- provide grip on a variety of different road surfaces
- withstand wear and tear
- withstand user abuse and neglect
- operate in any weather condition
- operate quietly
- be produced from environmentally friendly materials
- be re-cyclable
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In addition to the above, the average sized tyre will rotate
approximately 880 times within one mile and the average mileage for a
car tyre is 30,000 miles. This means during its service life the tyre
will rotate more than 26,000,000 times. Each time it is in contact with
the road it is deflected or distorted under the load of the vehicle and
hence it is deformed more times than most other components on a vehicle.
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