The function of the supporting wheel is to transmit the weight of the locomotive unit to the ground and roll on the track. In order to prevent derailment, the support rollers should also be able to prevent the crawler from causing lateral relative movement to it.
The support wheels often work in mud, water, ash, and sand, and are subject to strong impacts. The working conditions are extremely harsh and the rims are easy to wear.
The requirements for the supporting wheels are: wear-resistant rims, reliable bearing seals, and low rolling resistance.