Solid Front Axle ( A Brief Insight)

In this brief article, we will discuss the Solid Front Axle, the types of Solid Front axles and Solid Front axle suspension. We will also discuss some of the advantages and drawbacks with the solid front axle.

What is a Solid Front Axle?

From the Oxford definition, the word Axle means –

“..a rod or spindle (either fixed or rotating) passing through the center of a wheel or group of wheels…”

In a vehicle, a front solid axle is also called a ‘beam axle’, or a ‘rigid axle’. The Solid Front axle is basically a Solid or a Hollow Beam structure holding the left and right wheels through Kingpin joints. 

A Solid front axle steering gear is mounted on either the right or left side. Because of this, the steering input will need to be transmitted across to the opposite wheel. In order to achieve this, the stub-Axles are connected to each other by a Steering Tie-rod using ball-joints.

What are the Different Types of Solid Axles?

There are basically 2 types of Solid Axles:

  • Live Axle
  • Dead Axle

Live Axle

The Word ‘Solid’ in “Solid front axle” does not necessarily mean that the axle can’t be hollow. A Live axle means that apart from the structural support that it provides to the left and right wheels, the axle also houses the Differential Gears and axle shafts that transmit power to drive the wheels. The axle will therefore need to be of hollow construction even though the name suggests otherwise. Vehicles with 4-wheel drive have a live axle at the front.

Dead Axle

A Dead axle can also be called a beam axle. A dead axle is mostly found in the front suspension of trucks that are rear wheel drive and is of the steerable type and ‘Non-Driven’. The axle beam is either straight or “Gooseneck” shaped. A Dead front axle means a Solid beam structure that would mostly have an ‘I-Shaped’ Cross-section in order to get maximum bending strength. The Stub-Axles are attached at each end using a Kingpin joint which is serviceable.

What is a Front Solid Axle Suspension?

A Solid Axle suspension can also be called a dependent suspension. The earliest form of suspension for the solid front axles was the leaf spring type. 

Because the left and right wheels are connected rigidly, the vertical motion of the left and right wheel is always coupled. In other words, when the left wheel went upwards over a bump, it pushed the right wheel to go downwards.

What are the Different Types of Solid Axle Suspension?

The different types of Solid Axle suspension are:

  • Leaf-spring
  • Air Suspension
  • Air-Leaf Suspension

Leaf Spring Front Axle Suspension

The Leafspring-type suspension is the most popular among all solid front axle suspension systems. A majority of rear wheel drive trucks and commercial vehicles have a leaf spring front solid axle suspension.

The most common type of leaf spring is a Semi-Elliptic leaf spring. It is basically a stack of slender steel strips stacked one above the other and clamped together. The chassis is hinged to the 2 edges of the leaf spring, whereas the middle of the leaf spring is clamped to the Solid Axle using a U–Bolt Clamping arrangement.

The leaf spring started out in the early 20th century as the most common type of suspension and can be found on the front suspension of almost all cars of right upto the 1940’s. Later on, in recent times, the Front Solid axle leaf spring setup became more extinct and are found only on Pickup trucks like the Land Rover Defender.

Front Axle Air Suspension

The front Solid axle Air Suspension is usually not available from the OEM as standard equipment. Air suspension would be available as a retro fitment Kit from aftermarket suspension specialist companies like Henrickson. 

The Kit would include all the frame brackets and a multi link  suspension which would be of either the 4-Link or 5-Link Type. The suspension Kit would consist of:

  • A compatible modified axle with control arm mounts
  • Frame brackets for control arm mounts
  • 2 upper control arms
  • 2 Lower Control arms
  • A panhard rod (in the case of a 5-Link type)

The upper and lower control arms take up the braking and acceleration and Roll and cornering loads coming from the tires in the case of the 4-Link setup. In many cases, a 4-link setup would flex under heavy cornering loads for vehicles that are performance-oriented. The 5-Link setup basically evolved to overcome this limitation. The Panhard Rod takes up Lateral inputs from the tires.

Air-Leaf Front Axle Suspension

Some truck OEMS offer Air-Leaf front suspension, like the AIR GLIDE 130 by Peterbilt. The Air-Leaf Suspension is also available as an aftermarket Upgrade. The front Air-Leaf suspension is similar to the front axle leaf spring suspension. The only change is that the factory semi-elliptic leaf springs would be replaced with single-Leaf Parabolic springs.

The advantage of having a leaf spring in series with the air bag is that the effective spring rate would be much softer than either the air bag or the leaf spring.

Advantages of a Solid Axle Suspension

  • A Solid axle’s biggest advantage is in its simplicity of design, Robustness and relatively low manufacturing cost
  • There are a lesser number of CV joints required in a Solid axle. The driveshafts for both the wheel ends are always straight and in line, as opposed to an independent suspension where separate driveshafts and joints are required at both wheel ends.
  • A Solid live axle housing is very rigid casing that protects the driveshafts and give them longer life
  • A Solid live axle would be cheaper and faster to develop, as opposed to a new Independent suspension which requires a comparatively higher engineering effort and expense. 
  • The number of parts and different types of joints involved in a solid live axle is lower and hence the number of maintenance issues and associated costs in comparison to an independent live axle.
  • The Solid axle Camber and Toe settings are fixed by the axle geometry and hence there is no change in the wheel alignment as the suspension moves from bump to rebound.
  • Because of the constant wheel settings, there are much lesser wheel alignment issues as compared to an independent suspension.

Drawbacks of the Solid Axle Suspension

  • Due to the higher unsprung mass and the inability of one wheel to follow the unevenness of the road without affecting the opposite wheel on the vehicle, the ride and handling quality in a solid axle suspension is much less as compared to an independent suspension.
  • In extreme off-roading conditions, where wheel articulations are important, an independent suspension is more capable of ensuring contact on all 4 tires as compared to a solid axle suspension.
  • The axle beam becomes the lowest point in the underbody of the vehicle and therefore the primary influence in ground clearance. In extreme off-roading conditions, this is a limitation that is overcome in an independent suspension setup.

Conclusion

In this brief article, we have discussed the Solid Front Axle, the types of Solid Front axles and Solid Front axle suspension. We have also discussed some of the advantages and drawbacks with the solid front axle.

In case of any queries or comments, please feel free to ask.

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