c) Cost of lubricating oil, filter and grease

The quantity of lubricating oil, filter and grease required depends on operating hours, frequency of changes, engine characteristics and working conditions at the job site. The equipment manufacturer guidelines or past data from experience of similar equipment in similar working conditions can be used to estimate of time period between the changes.

The quantity of lubricating oil required by an engine is equal to the amount added during complete change plus the small amount added between the changes. The quantity of lubricating oil required by engine can be calculated by using the following relationship.

----------------------------------(4.3)

Where

q l = quantity of oil required in gal/h

hp = rated horsepower of the engine

f = operating factor

c = capacity of crankcase in gallons

t = number of hours (i.e. duration) between the oil changes

The term 0.006 lb/hp-h in the above equation is based on the assumption that the quantity of lubricating oil required per rated horsepower hour between the changes is 0.006 lb and 7.4 lb/gal is the conversion factor. The operating factor (f ) in the above equation depends on throttle load factor and the efficiency factor i.e. operating efficiency. Manufacturer's guidelines or past experience from similar equipment under similar working conditions can be used to calculate the cost of these items. The hourly cost of lubricating oil, filter and grease can be calculated from hourly consumption quantities. It may be noted here that the quantity of oil required in SI unit system can also be obtained by using the appropriate conversion factors in the above equation.

d) Tire cost

The cost of pneumatic tires (rubber tires) is considered as a part of operating cost. The tire cost includes the tire repair and replacement charges. The service life of tires is generally shorter than that of the equipment as the tires wear out at a faster rate than the equipment. The life of tires varies according to extent of wear it is subjected to, which depends on the job site conditions. Tire repair charges can be calculated as a certain percentage of tire depreciation cost. The past data from similar operating and project site conditions and tire and equipment manufacturer guidelines can be used to estimate the expected life of tires. The hourly tire repair and replacement cost can be calculated by dividing the sum of the cost of a set of tires and repair charges by the life of tires in hours.