During WWII the "train" looking wheels were called bogie wheels. During the Vietnam War no US tank had bogies; all US tanks (as well as the NVA enemy tanks) had ROAD WHEELS.
Generally speaking, a modern tank uses a layout consisting of 3 or 4 different wheel types.
- The drive sprocket (or drive wheel) is either in the upper rear or upper front corner, and is attached to the engine. It provides power to the track.
- The idler (or tension wheel) is in the opposition position as the drive sprocket (i.e. either the upper rear or upper front position)
- Road wheels are the large main wheels on the ground side of the track, and usually number between 5 and 8, depending on the size of the wheels and the length of the tank. These wheels bear the weight of the tank.
- Return rollers are much smaller wheels (maybe 15% or less of the diameter of the road wheels) aligned along the top edge of the track, numbering usually 2-4. They keep the track from sliding around, enabling better "track dynamics", which improve performance. Return rollers are not present on all tank designs (particularly, older designs sometimes eschewed them), but seem to be pretty universal in today's tanks.
