What is Tyres and its types and designation? - Mechdor

 Tyres

The tyre is a circular and ring-like part of a vehicle that comes in contact with the ground. Tyres are fitted on rims and are filled with compressed air. Since its invention, natural rubber has been the most widely used material in the manufacturing of tyres. However, modern tyres also employ materials like synthetic. Rubber, fabric, steel wires, black carbon and more compounds. Tyres find a place in a wide range of locomotives, from bicycles to aeroplanes.

The tyres basically perform the following function:-

1. It supports the vehicle's weight.

2. It transfers the traction and braking force.

3. It changes and maintains the direction of travel.

4. It absorbs road shocks (due to road irregularities) by acting as a spring in the total suspension system.

A tyre may have a cross-ply construction or a radial ply construction, as shown in the figure. In the cross-ply tyre construction, the alternate layers of cords run in opposite diagonal directions. It is also known as cross-bias tyre construction. In radial-ply tyre construction, the cords run radially from bead to bead.

The basic structure of a tyre consists of the following components.:-

1. Tread:- It is the part that comes into contact with the road surface. The treads are made from a mixture of many different kinds of natural and synthetic rubbers. It protects the body and provides high grip, longer life, manoeuvrability and durability to the tyre.

2. Steel belts:- In the steel-belted radial tyres, belts made from steel are used to reinforce the area under the tread. These belts provide puncture resistance and help the tyres stay flat, so that it makes the best contact with the road.

3. Bead wires:- The bead is a loop of high-strength steel cable coated with rubber. It gives the tyre the strength it needs to stay seated on the wheel rim and to handle the forces applied by the tyre mounting machines when tyres are installed on rims.

4. Body:-  It consists of inflation pressure and endures load and road shock. The body is made up of several layers of different fabrics, called plies. The most commonly used ply fabric is a polyester cord.

5. Sidewall:- It is the most flexible part of the tyre and provides lateral stability to the tyre.

Advantages of Radial Tyres over Cross-bias tyres:-

The following are the advantages of radial tyres over cross-bias tyres:-

1. Better safety (shorter braking distance):- The braking efficiency of radial tyres on wet roads is better due to stiffer tread and greater sidewall flexibility.

2. Better control:- On turning, a radial tyre has less tendency to distort and leaves the road from one side. Thus, there is better contact of the tyre and hence great stability and precise steering are obtained.

3. Fewer punctures:- The radial tyres are provided with dual steel belts, due to which there is less tendency of a puncture in radial tyres.

4. Lower fuel consumption:- The rolling resistance of radial tyres is lower due to sidewall rigidity and stiffer tread, due to which fuel consumption is lower.

5. Greater resistance to wear (longer tread life):- The life of the tyre is normally increased by 50%. This is due to less slip and fewer internal losses.

The advantage of a bias-ply tyre over a radial-ply tyre is a smoother ride at low speeds of the vehicle.

How to Read Tyre Size Designation:-

The tyres are generally specified and designated by the nominal size of their sectional width and the wheel rim diameter.

• The cross-bias ply tyres are generally designated as. 7.5 × 14 × 6PR.

1.  The section width or thickness of the tyre from shoulder to shoulder is 7.5 inches.

2. The diameter of the wheel rim is 14 inches.

3. PR means ply rating. This represents the maximum recommended load that the tyre can carry when used in a specific condition. It is an index of tyre strength and does not necessarily represent the number of cord plies in the tyre.

• The radial tyres are generally designated as 145/70 R 12 69 S.

1. The section width or thickness of the tyre from shoulder to shoulder is 145mm.

2. The aspect ratio is 70%. The aspect ratio is defined as the ratio of the section height to the section width of the tyre. In this case, it means the section height is 70% off section width, i.e. 101.5 mm.

3. R represents that the tyre is radial.

4. The diameter of the wheel rim is 12 inches.

5. The load index is 69. The load index defines the maximum load (mass in kg) a tyre can carry under specific conditions.

6. The speed symbol is S. The speed symbol defines the maximum speed for which the tyre is rated to carry a load corresponding to its load index, under specific conditions.

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