Tyre Function

Numerous qualities are required of a tyre, including the following:

• resistance to wear;
• resistance to impacts and cuts;
• comfort;
• grip;
• flotation;
• traction;
• stability;
• low rolling resistance;
• suitable for retreading;
• suitable for repair;
• resistance to heat;
• ability to carry load;
• ability to travel at sustained design speeds.

Rules which allow tyres to be used to their full potential, leading to increased productivity and reduced operating costs on a site.

The tyre is at rest (position 1); as it rotates (position 2), the sidewalls are compressed, causing heat to be generated in the tyre’s internal components until contact with the ground (position 3) is attained. The heat generated then reduces as the tyre returns to its initial position (position 1).

If the action described above is too rapid, the optimum temperature for the correct functioning of the tyre is exceeded and the tyre is likely to become damaged.

A tyre is usually inflated with air (or nitrogen), and provides contact between the ground and the machine. It is subject to a large number of constraints:

• pressure;
• load;
• speed;
• temperature;
• nature of the ground;
• condition of the haul roads.

The optimum tyre will be the one which is able to satisfy each of these constraints to give the best overall compromise.

Economical load limit of the tyre in use

This is the optimal design load limit beyond which tyre performance is compromised.

If the tyre is operated within this load and pressure limit, optimum performance can be obtained in terms of tread life, ride comfort, resistance to cuts and impacts, etc.

These load and pressure limits are published in our technical documentation and reflect the requirements of the international standards.

It is possible to use our tyres beyond the published load limits for economical use (but remaining within the maximum values indicated in the charts). However, this will reduce the tyre’s tread life and its resistance to damage.

In order to ensure that tyres are being used under optimum conditions, operators are advised to:

• determine tyre loads by weighing the vehicles by axle (preferably by tyre position) under their normal operating loads and set pressures accordingly;
• never exceed the maximum distance that the tyre is designed to travel in any one hour.

Main causes of damage

A large number of earthmover tyres are damaged as a result of:

• Underinflation: if a tyre is run in an underinflated condition for a given load and speed, the increased deflection will lead to i) an increase in its internal operating temperature, and ii) fatigue.
   
• Overinflation: if a tyre is run in an overinflated condition for a given load and speed, the tread contact area on the ground is reduced leading to i) increased wear and, ii) reduced resistance to cuts and impact damages. 
   
• Overloading: causes increased tread wear, greater deflection of the sidewalls with an increase in tyre temperature, and fatigue.
   
• Excessive speed: causes increase in the internal temperature of the tyre, fatigue and rapid tread wear. 
   
• Severe impacts. 
   
• or a combination of the above.

Damages can be caused or made worse by:

• lateral forces generated in curves with very small radii;
• impacts on poorly maintained road surfaces.

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