Crawler wheels are a pair of wheels that are carrying load of machinery and running that machinery on two endless tracks. There are two set of wheels under the track. Front pair wheel named idler wheel is used for guiding the track. While rare under carrying wheel is named as sprocket wheel and this wheel provide the power during motion of machine in either direction.
Crawler track has a very strong grip with any kind of surface. Therefore, machinery with this type of wheel is most commonly used in hilly areas where slope is more and center of gravity is low. Crawler carrying machine has a low ground pressure because, load distribute on large areas. Load of the machine distribute uniformly on the whole track and hence low ground pressure per square feet.
Due to low ground pressure, crawler type machines are also used for those soils having little bearing capacity. Bearing capacity is the strength of soil to bear load before failure. If bearing capacity is more than this mean underlying soil has high strength against load and if value is small then this mean underlying soil is cohesive soil and has low strength against load.
In case of wheel type machine, where machine runs on four tires and has a high ground pressure. This is because of point load acting only under each wheel. Point load acts only on area that is covered by wheel or area that is in contact with wheel at time. Rest of area under machinery remains inactive because of no contact with the machine. Therefore, due to little contact area it has high ground pressure.
Due to high ground pressure, this type of machinery is not suitable for areas where bearing capacity of underlying strata is very weak or for cohesive soils. But, there is an advantage of machine with normal wheels. This machine can move from one place to another on roads, highways streets etc… but for transporting crawler type machine from one place to another. Special arrangements are required for transporting from one site to another. Because it damaged the road with the teeth that are on endless tracks. These teeth on tracks are for ground grip. When machine moves then these teeth moves into the earth strata for the sake of grip.