Tyres
Necessity and Functions
● Tyres are necessary for safe driving as they are link with road and vehicle.
● Different parts of the tyre are illustrated. A tyre is made from rubberized fabric piles over a rubber liner and the edges of the piles are wrapped around a wire bead, which holds the tyre to the wheel rim.
● The fabric piles are covered with a rubber compound tread and a different rubber compound for the side walls. The tyre is cured in a mould to vulcanize the parts into a single unit and form the tread design.
● A tyre is a cushion provided with an automobile wheel against shock.
● Tyre must be large and strong to support the load they are expected to carry.
● They absorb shocks from road irregularities. They must develop tractive force on accelerating, cornering and braking.
● It transmits driving and braking forces of the road.
● Provides cornering power for smooth steering.
● Maintain steering and directional control.
Desirable Properties (Requirement) of Good Tyres :
Properties (requirement) of good tyres
1. Load carrying
2. Cushioning
3. Uniform wear
4. Balancing
5. Non skidding
6. Fuel or power consumption
7. Noise
1. Load carrying : It must be strong to carry the vehicle load and also alternate stress set up in cache revolution to resist damage.
2. Cushioning : It should be flexible to absorb vibration, shocks and impacts set up by the road surface and provide cushioning effect. So it must provide comfortable ride to passengers.
3. Uniform wear : Tyre must wear uniformly over its outer circumference to provide a long life.
4. Balancing : It must be balance statically as well as dynamically. It must respond accurately to steering without deflection by the ridge on the road.
5. Non skidding : It should not skid or slip on the road surface in all weathers condition providing grip for traction, comering, accelerating and braking without overheating.
6. Fuel or power consumption : During rolling on road surface, it must consume minimum fuel and power to get fuel economy.
7. Noise: It must create minimum noise while rolling on road surface.
Types of Tyres :
In general, the tyres are classified in two type:
(a) Solid tyre
(b) Pneumatic or air filled tyre
1. On the basis of pressure and volume
(i) High pressure tyre
(ii) Conventional tyre
(iii) Super cushion tyre
2. On the basis of construction
(i) Tube tyre
(ii) Tubeless tyre
3. Carcass types tyre
(a) Cross ply tyre
(b) Radial ply tyre
(c) Belted bias tyre
(a) Solid tyre: These are of limited use specially in industrial applications.
(b) Pneumatic or air filled tyre : In this type an air is acts as a cushioning medium confined in an inner tube. These classified as below.
1. On the basis of pressure and volume
(i) High pressure tyre (Pressure upto 4.2 Kg/cm.sq)
(ii) Conventional tyre (Pressure range 1.68 Kg/cm.sq to 2.8 Kg/cm.sq)
(iii) Super cushion tyre (Pressure range 1.4 Kg/cm.sq to1.68 Kg/cm.sq)
2. On the basis of construction
(i) Tube tyre
(ii) Tubeless tyre3. Carcass types tyre:
(a) Cross ply tyre
(b) Radial ply tyre
(c) Belted bias tyre
(i) Tube Tyre
● It is a traditional tyre. It encloses a tube in which air is forced to a high pressure as a cushioning medium.
● The tyre is manufactured from different parts that are moulded together to form a complete structure. The parts are:
(i) Liner
(ii) Tread layer(iii) Cord and piles
(iv) Bead or rib(v) Side wall
(vi) Outer rubber covering
The liner and plies form together called as carcass or inner casing. The tyre is manufactured by vulcanization process in which rubber is heated under pressure to obtain required form and characteristics.
(1) Carcass
● This is a horseshoe-shaped inner lining of the tyre. The carcass forms the backbone of the tyre construction and the tread, bead and walls all are moulded on to these cord piles.
● It provides strength and body to the tyre without side wall rubber. It is made from overlapping plies, consist of parallel card of rayon, nylon, fiber glass, polyester, embedded in a layer of rubber.
● The piles ends are wound around the beads and bounded to the side walls. Air pressure acts evenly against the interior surface producing tension in the carcass.
● Because of the air pressure carcass support and resist the weight of the vehicle. The outer rubber covering is moulded around the carcass.
● The ply rating indicate the approximate number of plies in the tyre,
(2) Liner
● Liner is a thin air light layer of rubber on inner side of the carcass.
(3) Bead
● This forms the inner edge of the tyre and locates and centralizes the cover on to the wheel rim. It has the rigidity and strength required to support the carcass.
● To achieve this endless wire core is moulded circumferentially through the bead.
● It is a bundle of thin steel wires. These are fit around the wheel rim and the wires are wrapped with a fabric to hold them.
● These are embedded in rubber to prevent the tyre from stretching and protect from leaving the wheel rim. By use of heavier gauge wire the strength of bead increases.
(4) Tread
● It is a part of tyre design considerably influences the tyre's gripping, road holding ability and working life.
● It helps to run the vehicle on road surface when the wheel rolls. The tread rubber is groove to provide maximum frictional force giving good traction and avoiding skidding, minimize noise.
● Some chamber is provided circumferentially on outside which give additional stability and rigidity.
● The tread are assembled in a separate piece of soft rubber which changes or convert to compound of high resistance to wear after vulcanization.
(5) Breaker
● The two top plies of the tyre are referred to as breaker.
● They are widely spaced as compared to other plies.
● These plies helps in spreading the shocks received from the road.
(6) Side wall
● This constitutes the outside rubber covering of the carcass between the bead and the tyre tread.
● The amount of protection provided to the carcass and the stiffness of the tyre during deflection depends on the thickness of side wall.
● It connects the bead to the tread and made of different grade rubber. The rubber has quality to absorb road shock and protect cord and piles.
● The side walls are thinner and the rubber used is relatively porous in nature.
● The outer portion of the tyre which rolls on the road is made of synthetic rubber and is called tread. At the inner edges,beads are formed by reinforcing with steel wires.
(ii) Tubeless Tyre
● Tubeless tyre is a advance version of conventional tube tyre.
● The basic difference is that tubeless tyre does not enclose a separate inner tube. In this type of tyre there is a special air retaining bead arrangement.
● This type of tyre is directly mounted on the rim.
● The air under pressure is filled in the tyre itself through a non return valve is fitted to the rim.
● It is a toroidal shape inflatable envelope made of outer cover with a special inner lining, It does not employ any sealant and depends upon airtight card fabric to retain the air.
● The bead is the air tight part which fit on the circumference of the wheel rim. It consist of bead cores made of number of strand of steel wire.
● Carcass is the main structural element that takes the load and consist of rubber bounded cords and beads.
● Tread is the surface part that come in contact with road surface made of synthetic rubber.
● Non return valve is an integral part which allows high pressure air in one way.
● The tubeless tyre is lighter and runs cooler than the tube tyre.
Advantages
Advantages of tubeless tyre
1. Simple assembly
2. Improve safety
3. Better cooling
4. Less unsprung weight
1. Simple assembly : The tubeless tyre are easier to fit and no danger of puncture during assembly.
2. Improve safety : When punctured it deflects slowly in contrast to tube tyre where air leaks out fast. This is because of soft lining has self-sealing effect.
3. A temporary puncture repair can be made without removing the wheel by stopping the hole with a special rubber plug.
◆ However tubeless tyre cannot be used in spoked wheels since in that case the rim is perforated.
◆ The tubeless tyre should be inspected periodically and all the foreign objects should be removed.
◆ If the objects are allowed to remain in the tubeless tyre they tends to enlarge the puncture and repair became more difficult. The chances of sudden tyre puncture leading to accident are reduced.
4. Better cooling : Heat generated during running is directly pass from the tyre to the surrounding.
5. Lesser unsprung weight: The tubeless tyre is lighter and runs cooler than the tube tyre.
Disadvantages
Disadvantages of tubeless tyre
1. Early replacement
2. Cost
3. Difficult puncture detection
1. Early replacement
Due to frequent removal of tyre in case of puncture repair. Refitting over the rim, the air tightness between the rim an tyre became weak.
2. Cost:
Due to special air sealing the cost is 20 to 30% more.
3. Difficult puncture detection
Since this tyre retain air even in case of puncture, so it is difficult to realise a puncture in the tyre.
4. Not suitable for spoke wheel.
Comparison of Tubed Tyres with Tubeless Tyres
Tubed tyres → Tubeless tyres
1. Suitable for the spoke wheel. → Not suitable for spoke wheel.
2. Chance of air leakage is more. →Chance of air leakage is less.
3. Tube is provided inside the tyre. → Air retaining liner is provided inside the tyre.
4. Air sealing quality is poor. →Better air sealing quality.
5. Fitting of these tyres is difficult. → These are easier to fit.
6. Strength of these tyres is more.→ Strength of these tyres is less.
(a) Radial Ply Tyre
● The radial ply tyre have plies running from bead to bead across the crown at right angle to rotation.
● On the side walls the direction of these plies IS radial and hence the name is radial ply tyre. In between tyre tread there are cord or breakers which run around the circumference.
● The angle between the cord varies in the range of 18° to 25°. The material used for manufacturing will be depend on load to carry and lateral stiffness, so accordingly by the number of layer on tyre is designed and manufactured.
● The tyre construction is so design to reduces cornering wear and hence increases the tyre life but these are more expensive at low speed.
● The radial plies provide greater reliability and comfort but does not gives the directional stability because of breakers since they firmly restrict any lateral stretching of the tyre tread.
● These tyres are expensive compared to cross ply tyre. But they are more efficient for fuel economy and quick steering response and puncture resistance.
(b) Cross Ply Tyre Construction (Bias Ply Carcass)
● In the cross bias tyre construction the alternate layers of cords run in opposite diagonal directions. It is also known as cross bias tyre construction,
● Bias-ply allows the tyre to squirm as it moves through the tyre foot print or contact patch.
◆ The cross-bias cord angle runs from 30 to 40 degrees. This provides a cross-cord side wall, which gives required strength to transfer acceleration and braking torque.
● This type of tyres have better wear and road holding characteristics. But they must not be fitted on the front wheels only.
● Fitted radial tyres all round, or use cross ply on the front and radial ply tyres on the rear wheels, otherwise the characteristic will be seriously impaired.
(c) Belted Bias Type
● It is a combination of above two type (Radial ply and belted bias type).
● In belted tyres the tread stability and reduction of squirm results in upto 100% improvement in tyre running compared to bias-ply tyres.
● The basic construction is the bias ply over which run a number of baker belts.
