In simple terms TKPH (or for metrically challenged TMPH ) is a measure of the amount of work a tyre is capable of performing before it reaches its critical operating temperature.

Tyres are like humans in a lot of ways, our physical work generates heat, as does a tyre. The more load we carry the hotter we get, as does a tyre. The faster we move the hotter we get, as does a tyre. Most work is achieved when load and speed are balanced, for a human or a tyre.

The degree of work performed relates to the load carried over a distance in time. Work = load x distance x time. or tonne x kilometre x hour TKPH.

The load a tyre experiences for the purposes of the calculation is the average or mean load. A truck hauls loaded one way and returns unloaded. During loaded and unloaded sections of the haul the trucks weight distribution changes. These factors are considered in the mean tyre load calculations.

The speed of the haul is not just the maximum speed the truck achieves (though this is important when considering absolute tyre load) it is the average speed of the complete cycle the truck makes, ie loaded haul maybe up ramp and return unloaded down ramp so the actual road speed can vary. The time for loading and dumping is also considered in the speed calculation.

Why is this information important to a mining operation? TKPH data is used in the tyre selection process. The work load determines tyre construction, tread pattern, pattern depth or tread class (E4, E3 or E2) and most importantly tread compounding. A large OTR tyre can fail from heat related damage inside a single days operations if the tyres specification is incorrect. Such heat damage usually results in a new tyre being destined for the scrap heap, with corresponding expense to the tyre budget.

Numerous other factors are included into the selection process such as ambient conditions, length of haul, time of operations. Always seek specialist advice when selecting OTR tyres for your operation, a suspect decision may result in a very high cost not only in tyres.

COBA use various methods to analyse TKPH requirements before placing tyres onto machines. Such methods may include physical observations, interrogation of on board computing or dispatch systems and vehicle simulation programs. Prior to making any pattern or compound changes a TKPH survey is highly recommended as part of any due diligence process.

A tyre that has exceeded its TKPH specification may suffer irreversible damage to its construction, a tyre that has operated on or near its maximum may suffer a reduction in overall life performance, just as a human who has worked physically hard may suffer premature aging.

COBA engineers can determine by internal testing whether a tyre has been exposed to over specification operations. A tyre is a structure which is designed to support a load at speed, exceeding the specification will result in the tyre suffering mechanical damage which can be easily observed.

Like most mechanical objects tyres will display evidence of over work. Caterpillar have employed what they call the 10 - 10 20 rule. This rule mandates that only 10% of loads can be 10% over specification and no loads can be 20% over specification. The many tyre related organisations around the globe (IT&RA, JATMA, ETRTO, AT&RA) establish load and pressure specifications yet many end users ignore these specifications and wonder why their tyres do meet the expected performance levels.

OTR tyres are not equipped with the many warning devices that an engine has, hence there are no warning of overheating, under pressure or over speed. It is the operators responsibility to ensure that manufacturers specifications are observed. Failure to adhere to such specifications can endanger life and property as well as voiding any warranty considerations that may be adjudged.