Railroads: Components of Rolling Resistance
One may define rolling resistance in the broad sense as the sum of components): 1. Wheel bearing resistance 2. Pure rolling resistance 3.Sliding of the wheel on the rail 4. Loss of energy to the roadbed (and earth) 5. Loss of energy to oscillation of railway rolling stock.
The wheel bearing resistance may be reported as a specific resistance at the wheel rim, for example as a Crr. Railroads normally use roller bearings which are either cylindrical (Russia) or tapered (United States). The specific rolling resistance (in of Russian bearings varies with both wheel loading and speed. It is lowest with high axle loads and intermediate speeds of 60–80 km/h with a Crr of 0.00013 (axle load of 21 tonnes). For empty freight cars with axle loads of 5.5 tonnes, Crr goes up to 0.00020 at 60 km/h but at a low speed of 20 km/h it increases to 0.00024 and at a high speed (for freight trains) of 120 km/h it is 0.00028. The Crr obtained above is added to the Crr of the other components to obtain the total Crr for the wheels.
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