Ton-Kilometre per Hour

Earth-moving and mining tyres have become increasingly important with the development of ultra large construction vehicles. The primary task of these heavy-duty tyres is to haul maximum loads faster, over longer distances. The inevitable consequence of heavy hauling is heat buildup in the tyres. As tyres have limited resistance to heat, deterioration of the tyre may begin at any early stage of operations. Accordingly it is necessary, when selecting tyres, to determine the amount of work which will keep the tyre within a safe range to avoid over-heating.

The amount of work done under the given conditions and within a safe range is known as "Ton-Kilometre-Per-Hour" and can be calculated in a number of ways.

Method 1
 
TKPH = ( Mean Vehicle Load  *  Work Day Average Speed * % Axle Load Distribution ) / ( Number of tyres per axle * 100)

Method 2
 
TKPH =  Mean Tyre Load (tons) * Work Day Average Speed (km/h)

Mean Tyre Load = 1/2 (Loaded Mass + Empty Mass) of tyre being examined.

Work-day Average Speed = ( Round trip distance in kilometers * number of cycles per day ) / ( total hours of operation per day )

Load calculations

Refer method 1

Weigh the vehicle one axle at a time for each load to be weighed. Determine the mean loaded mass of the vehicle by adding the individual axle masses for each load. Determine the empty mass of the vehicle by weighing the individual axles and then adding them together. The percentage load distribution can then be determined by establishing what percentage of the load is carried by the front axle and rear axle(s) individually.

Mean vehicle load

Refer method 1

The mean vehicle load is the average mass of the vehicle during its working shift (or day). This is determined as follows:

Mean Veh. load = ( Mean Gross Veh. Mass + Empty Vehicle Mass ) / 2

Mean tyre load

Refer method 2

The mean load is the average load carried by the tyre during its working day, and is calculated as follows:

Mean tyre load = Average vehicle load * % load distribution of tyre
(% Load distribution is calulated below but here the individual tyres, not axles, are weighed)

% Load distribution

Refer method 1

The percent load distribution is the portion of the load carried by each individual axle. This is determined as follows:

% Load Distribution = ( Mean Axle Loading * 100 ) / Mean Gross Vehicle Mass 
 
Please note: All wheels on one axle must be on the scale for Axle load distribution and only one wheel must be on the scale for Tyre Load Distribution.

Calculation of Working Day Average Speed (WDAS)

There are two methods of calculating the WDAS:

(1) Measure the total distance covered by the vehicle in one shift or day, (km). Determine the total hours worked by the vehicle per shift per day.

WDAS = Total Distance Covered / Total Hours Worked

(2) Measure the round trip distance, (km). Determine the number of cycles per shift or day. Determine the hours worked by the vehicle per shift or day.

WDAS = (Round trip distance * No. of Cycles) / Total Hrs Operated