It’s the air pressure inside a tire that supports the load, not the tire. And since air is a gas, it expands when heated and contracts when cooled. That’s why proper tire inflation is critical in mining operations. Improper tire inflation can result in:
Over inflation issues…
Increased risk of rock cuts
Loss of traction
Vehicle vibration, leading to poor vehicle handling and payload spillage
Under inflation issues…
Irregular or uneven tire tread wear
Sidewall radial cracks
Loose or broken cords inside tires
Belt edge separation
Here’s where “cold inflation” pressure comes in. In a mining tire, it’s normal for the air pressure to increase by 30 psi once operating temperature is achieved. So, to ensure a tire is at the correct pressure when operating temperatures are reached, manufacturers specify a cold inflation pressure. Cold inflation pressure is the pressure of a tire at a fixed, indexed temperature, usually 20°C or 68°F. The cold inflation pressure is always lower than the ideal working pressure because the pressure will increase as the temperature increases. For example, when a tire manufacturer wants the pressure in a working tire to be between 120 and 130 psi, they may specify a cold inflation pressure of 105 psi.
Understanding and utilizing cold inflation pressure provides the following benefits:
By inflating a tire at an indexed temperature, a tire fitter can confidently avoid the risk of over or under inflation when the tire is put into service. Once inflated to the correct cold inflation pressure, the operating tire pressure and temperature should increase to the recommended working values set by the tire manufacturer.
By knowing the calculated cold inflation pressure, operators are always aware of the amount of air in a tire and slow leaks can be caught early, before excess tire wear and fuel consumption occur.
When an operator is aware of a tire’s cold inflation pressure, that pressure can be safely and accurately altered while a vehicle is in service. This allows operators to change the cold inflation pressure for different loads without waiting for the tire to cool.
Maintaining equal cold inflation pressure across all wheels on a vehicle allows the load to be evenly distributed. No tire will work harder than any other, and excessive, hazardous heat build-up will be avoided.
Optimum tire life and fuel economy occur at the manufacturer’s recommended cold inflation values.
It’s evident that the principles and practice of cold inflation pressure are key to reducing tire-related problems and lead to more efficient, profitable and safe mining operations. However, determining the correct cold inflation pressure is easier said than done. Relying on the tire manufacturer’s Ton Kilometer Per Hour (TKPH) rating is not ideal, considering the pressure of a tire can change dramatically with temperature.
Utilizing a Tire Pressure and Temperature Monitoring System (TPMS) offers invaluable insight into tire pressure and temperature relationships, using data log history and calculated cold pressure analysis. In fact, some TPMS have taken the guess work out of cold inflation pressure by using the average pressure and the maximum temperature to calculate the cold inflation pressure automatically.
By understanding the importance of cold inflation pressure, and employing a TPMS to make its application easier, you will extend the life of your tires and improve the overall productivity of your operation.