• A dead axle, also called lazy axle, is not part of the drive train but is instead free-rotating. The rear axle of a front-wheel-drive car is usually a dead axle.
• Many trucks and trailers use dead axles for strictly load-bearing purposes. A dead axle located immediately in front of a drive axle is called a pusher axle.
• A tag axle is a dead axle situated behind a drive axle. Dead axles are also found on semi-trailers, farm equipment, and certain heavy construction machinery serving the same function.
• On some vehicles (such as motorcoaches), the tag axle may be steerable. In some designs the wheels on a lazy axle only come into contact with the ground when the load is significant, thus saving unnecessary tire wear.

Front dead axles

• The front dead axles called as rigid axles are straight axle, double drop axle, and fully drop axle type.
• These are made by drop forging from steel having 0.4% carbon or 1.3% nickel steel.
• The front axle is made of I section at the center portion. While the ends are made either circular or elliptical. The ‘I’ section construction takes bending loads due to the load of the vehicle and also the torque due to the braking of the wheels.
• To keep the chassis height low, the center portion of the front axle is given a downward sweep.
• It reduces the swing or sway of the vehicle while cornering and give greater stability as well as safety at high speed.
• The center of gravity of the road vehicle was lowered by dropping the entire center portion. The dead front axle transmits the weight of the front part of the vehicle to the road surface through the front wheels.
• It also carries the steering mechanism and absorbs shock due to road variation. The rigid type front axle was used in connection with leaf springs. The two longitudinal leaf springs fixed to the two spring seat on the axle beam.

• The principal advantage of the beam axle is its simplicity.
• This simplicity makes it very space-efficient and relatively cheap to manufacture.
• They are nearly universally used in heavy-duty trucks and most light and medium-duty pickup trucks, SUVs, and vans also use a beam axle, at least in the rear.
• Beam axles have an important advantage for off-road applications, as they provide better vehicle articulation and durability in a high load environment.
• This simplicity also makes it relatively easy to lift a vehicle.

• The drawbacks are that it does not allow each wheel to move independently in response to bumps, and the mass of the beam is part of the unsprung weight of the vehicle, which can further reduce ride quality.
• Also the cornering ability is typically worse than other suspension designs because the wheels have zero camber angle gain during body roll.

Types Of Rear Axle/Loading of different axle-hub arrangements

Half Floating Axle/Semi Floating 

In a half floating rear axle, the axle is at the center of the axle casing and the bearings are inside the axle casing. The weight of the vehicle is transmitted first to suspension spring, then to axle casing, then to the axle and finally to the ground.