Rear Suspension Types ( A brief overview)

In this brief article, we will discuss the different types of Rear Suspension, and their applications.

What are the 2 main types of Rear Suspension?

The 2 main types of rear suspension are:

  • Dependent axle suspension
  • Independent suspension

In the beginning of motoring history, till the right before World war II, almost all vehicles had Solid axles. The Solid axle suspension was basically known as the ‘Dependent’ Suspension. Later on in the evolution of passenger cars and racing cars came the vehicles that moved from a solid axle to independent wheel setups. The Dependent suspension still exists for SUV’s and pickup trucks, but the passenger car segment has largely moved on to ‘Independent’ and ‘Semi-independent’ suspension setups. 

What are the different types of Rear dependent axle suspension?

The different types of rear dependent axle suspension are:

  • Leaf-spring
  • Rear 3-Link suspension (Solid axle)
  • Rear 4-Link and 5-Link suspension (Solid axle)
  • Watts Linkage

Leaf Spring Solid Axle Suspension

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

The most common type of leaf spring is a Semi-Elliptic leaf spring.  In recent years, the ‘Parabolic’ type of leaf spring has become more common due to its lower weight and better ride comfort.

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 leaf spring setup became more extinct and are found only on Pickup trucks like the Ford F150 and the GMC Sierra.

The Rear 3-Link is arguably one of the most simple of all suspension setups. It is a suspension meant for a rear Solid live axle. It consists of 2 Trailing arms and a Panhard Rod. Due to this reason, the 3-Link Rear could also be called a Trailing arm suspension. The trailing arms constrain the axle’s longitudinal, Braking/acceleration and roll degrees of freedom. The Panhard Rod would constrain the lateral movement of the axle.

The Panhard Rod had the disadvantage that it constrained the axle to move up and down in an arc when looking from the vehicle rear. This would cause sideways movement of the axle from bump to rebound. The sideways movement leads to issues in handling predictability. In order to overcome this limitation the Watts Link was developed. The Watts link did the same job as a panhard rod but by splitting the panhard rod into 3 effective linkages.

This would allow the axle to move up and down in a straight line. Cars that came with a factory fitted Watts Link were the Ford Mustang (2005-2014) and the Dodge PT Cruiser (2001-2007).

The rear 5-Link is a rear solid axle suspension setup. The rear 4-Link is a step above the 3-Link, in that, instead of just 2 trailing arms, there are 2 Upper control arms as well. The 5-Link setup is the same as the 4-Link setup, with the addition of a 5th link, namely, the PanHard Rod. In many cases, when designing a rear 4-Link set-up, the need for a Panhard Rod can be eliminated. 

This is achieved by positioning the upper control arms in a ‘V’ shape. The ‘V’ shaped upper control arms, in combination with the lower control arms, can indirectly constrain the axle from sideways movement. The only caveat is that, once the actual control arms are attached through bushings, the combined effect of the bushings in the system must be sufficient to arrest axle lateral movement. In cases where the car is performance oriented, the Panhard rod may not be possible to eliminate due to the excessive lateral forces from the tires.

A well known example of a current day 5 -link solid axle rear suspension is the third generation (D23 platform) Nissan Navara, also known as the Nissan Frontier.

What are the different types of Rear Independent Suspension?

Independent suspension, by definition, is the suspension system where the vertical travel of one wheel is not dependent on the movement of the opposite side wheel. This means that the left and right side wheels move independently of each other. 

The different types of Rear Independent suspension systems are:

  • Transverse Leaf rear independent suspension
  • Rear 3-Link Independent Axle suspension
  • Rear 4-Link Independent Axle suspension
  • Rear 5-Link Independent Axle suspension

Transverse leaf-spring

A transverse leaf suspension has the leaf spring transversely mounted and clamped at the middle, leaving the two free ends that can bend along with the wheel movement. In the Corvette rear suspension, the transverse arrangement had a lateral control arm as well. The shock absorber has mounting provisions on the knuckle, quite similar to the double wishbone arrangement.

The transverse leaf suspension is quite rarely seen on cars nowadays. It was more prevalent in Triumphs, Heralds and Fiats from back in the 1960’s. It can be found on the front suspension of the Utility Van Iveco Daily, sold in Europe.

A Multi Link Suspension is a type of suspension which consists of 3 or more control links. In general, the suspension links of the Multi Link Setup, working in combination, are aimed at constraining 5 degrees of freedom of the knuckle. This would effectively leave the knuckle free in only one direction of motion, i.e., the vertical motion.

The 3-Link is the simplest form of a rear independent multi link suspension. The set consists of a Lateral arm or Lower control arm, a Trailing Arm and a MacPherson Strut. The MAcPhserson strut is technically a separate link, since it constrains the wheel-hub in both vertical and braking/acceleration.

The Rear Suspension is of independent 4 – link type, consisting of a Trailing arm, Upper Link, Lower Link and Toe Link. The 4-links consist of a trailing arm, a lower and upper control arm, and a Toe control arm. This is the performance-oriented version of the MQB platform. Due to this reason, the rear suspension set-up is complicated so as to resist high cornering forces of upto 1g.

The 5-links are, in essence, a sort of evolution from the Double Wishbone. The Upper Wishbone and Lower Wishbone are basically split into 2 separate links. The resulting setup consists of 2 lower and 2 upper control arms, and a Toe control arm (which is the Tie Rod from the Double Wishbone setup). The Upper and Lower Control arms, in combination, are designed to counteract the Braking, Acceleration and Roll loads. The Toe Arm counteracts the Aligning Torque that tries to steer the wheel when the vehicle corners.

Different OEMs have made their own version of this basic 5 Link setup. There is no constraint on the angle at which the Links to be oriented in the suspension, nor is there any limitation on length, as long as the 5-link setup can be packaged sensibly. So, some cars have one of the links as a Trailing arm, that is almost longitudinally mounted and designed to counter longitudinal vehicle loads.

  • 5 Link independent rear suspension is typically used where achieving good ride quality as well as good handling characteristics at the same time are of high priority
  • The design advantage that the Multi Link suspension offers is the possibility to alter a hardpoint (or joint location) in the suspension, without affecting other suspension geometry. An example is the Double Wishbone suspension where, in order to alter the steering ball-joint hardpoint, it would be necessary to change the shape of the control arm. In the case of the Multi-link, this modification can be done by modifying one control arm alone.
  • Using a Multi-link arrangement, it is possible to indirectly constrain a degree of freedom, without necessarily having a control arm in that particular direction. The net effect of links, when working together would achieve the desired constraint.
  • The MultiLink design allows more freedom of moving hardpoints in order to give the suspension “Anti-Squat” and “Anti-Dive” attributes
  • In Off Roading conditions, where wheel articulations are important, a multi link suspension would provide better “Flex” ability as compared to a Double Wishbone setup. The reason is that a multi-link would use 2 extra ball-joints (one for each control arm) and that a control arm, being smaller, does not need the kind of rigidity that a Wishbone arm requires.
  • The effective steering axis of the knuckle can be moved further outboard because of the 4 ball-joints (2 for the upper control arms and 2 for the lower control arms) instead of two in the case of the double wishbone.
  • The multiLink setup adds complexity and therefore visualization of the geometry would be difficult using a 2 Dimensional representation. The usage of 3D Computer Aided Design softwares becomes essential.
  • Developing a new Multi Link suspension would require comparatively more engineering effort and expense, as compared to an axle beam or a solid driven axle type of setup.
  • Due to the number of parts and complexity, an independent suspension solution could also result in higher manufacturing costs.
  • The number of maintenance issues and associated costs would increase according to the increased number of parts and different types of joints involved in the multiLink suspension.

Conclusion

In this brief article, we have discussed the different types of Rear Suspension, and their applications.

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

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