D6R Bulldozer Undercarriage Parts Front Idler Assy The four wheels refer to: rollers, drive wheels, idlers, and carrier pulleys. One belt refers to the tracks. As the name suggests, the rollers act as support and are located between the lower surface of the left/right beam of the chassis frame and the track. According to the tonnage of the excavator, there are usually 5-10 on one side. The driving wheel plays the role of driving the track, which is fixed on the travel motor, and the drive of the travel motor is transmitted to the track through the gear structure, usually one on each travel motor. The idlers act as guides the tracks, located at the opposite end of the drive wheels, usually two per excavator. The carrier roller plays the role of holding up the track, and according to the tonnage of the excavator, there are usually 1-2 carrier rollers on one side. Our products are according to the standard of OEM to manufacture.