Its purpose is to help in distributing the load on the rear
of the vehicle to the two live axles that it connects.
The three types of live axles that are used in
automotive and construction equipment are as follows:
semifloating, three-quarter floating, and full floating.
Wheels attached to live axles are the driving wheels.
Wheels attached to the outside of the driving wheels
make up dual wheels. Dual wheels give more traction
to the driving wheels and distribute the weight of the
vehicle over more surface. Consider dual wheels as
single wheels in describing vehicles.
The number of wheels is sometimes used to identify
equipment; for example, a 4 by 2 could be a passenger
car or a truck with four wheels, two of them driving. On
a 4 by 4 (fig. 2-18), power is delivered to the transfer
case where it is divided between the front and rear axle,
allowing all four wheels to drive. A 6 by 4 truck with
dual wheels in the rear is identified by six wheels, four
of which drive. When a live axle is in front, the truck
becomes a 6 by 6 (fig. 2-19), in which all six wheels
Figure 2-19.Six-wheeled drive transmission.