Tyres: Function, Structure & Cross Bias vs Radial Ply

What is function of tyres? Basic structure and components of tyres. Advantages of radial tyres over cross-bias tyres.

The tyres basically perform the following functions:

  1. It supports the vehicle weight,
  2. It transfers the traction and braking force,
  3. It changes and maintain the direction of travel, and
  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 Figure (a) and (b) respectively. 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 tyre consists of the following components:

1. Tread

It is the part which comes into contact with the road surface. The tread is made from a mixture of many different kinds of natural and synthetic rubbers. It protects the body and provides high grip, longer life, maneuverability and durability to the tyre.

2. Steel belts

In 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 tyre stay flat so that it make?, 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 sustains the inflation pressure and endures load and road shocks. The body is made up of several layers of different fabrics, called plies. The most commonly used ply fabric is polyester cord.

5. Sidewall

It is the most flexible part of the tyre and provides the lateral stability to the tyre.

Radial Tyres vs Cross-bias Tyres

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 side wall flexibility.

2. Better control

On turning, a radial tyre has less tendency to distort and lift off the road from one side. Thus, there is a better contact of 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 puncture in radial tyres.

4. Lower fuel consumption

The rolling resistance of radial tyres is lower due to side wall 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 less internal losses.

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

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