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Equipment Tests > 4WD Suspension Systems
4WD Suspension Systems
Issue: March 2001
Words by Mathieu Raudonikis
Your vehicle's suspension is the all-important link between its wheels and tyres and the load-bearing platform, ie: the chassis or monocoque. Its function is not only to provide a smooth ride for the vehicle's load (including the occupants) but to maintain the maximum permissible contact patch between the tyres and the road surface. It does this by absorbing some of the lateral loads placed on the vehicle during manoeuvres.
To absorb these loads the suspension uses a system of springs and dampers placed in between the wheel mounting hubs and the chassis. On 4WD vehicles the springs come in a variety of designs but for the most part they will be either be coil, leaf or torsion bar types. Less common are air bag or air springs but their use is becoming more widespread with the availability of quality kits from the aftermarket.
The dampers, or shock absorbers, are normally a telescopic cartridge that hydraulically displaces oil or gas through an orifice to dampen oscillations in the spring.
The springs and dampers can be set up under the vehicle a number of ways but basically they all do the same thing. Traditionally most 4WD vehicles use a 'live-axle' suspension set-up. This is where the entire axle assembly including the differential, its housing, the axles, hubs, brakes, wheels and tyres are all suspended away from the chassis. This robust system is great for 4WDs and heavy vehicles as it delivers long wheel travel and the differential housing protects many of the axle components from road damage. Its shortcomings however, are that because the wheels on either side of the axle are linked by the axle housing they can't act independently of each other and thus when the wheel on one side drops into a pothole or bounces over a bump, an opposing action is transferred to the wheel on the opposite end of the axle, affecting that wheel's contact with the road as well as the wheel that hit the obstacle. Also the high unsprung weight of the axle with the wheels and tyres affects the ride quality and the suspension's ability to keep the tyres on the ground. Examples of 4WDs with live axles both front and rear include Nissan Patrols, Land Rovers and non-IFS Toyota LandCruisers.
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The alternative to the 'live-axle' design is independent suspension. With this design the differential is mounted directly to the chassis and is connected to the hubs and wheels via constant velocity joints and exposed drive shafts. This allows each wheel to act independently of the other and the unsprung weight is reduced because the diff is now mounted to the chassis and there's no heavy axle housing. The downside of independent suspension is that most designs offer less wheel travel than a live-axle set-up, but the improvements in ride quality and handling far outweigh this. Examples of full independent suspension include the NM Pajero, Toyota RAV4, Hummer and Subaru Forester. Many 4WD vehicles have independent front suspension (IFS) with a live rear axle. These include Holden Jackaroo, Toyota Prado, modern HiLuxes, Nissan Pathfinder and the Lexus LX470.
Whatever set up your vehicle has, be it leaf, coil or torsion bar sprung, dual live-axle, independent front or full four-wheel independent suspension, the vehicle manufacturer has spent millions of dollars and thousands of man-hours designing and manufacturing it to be just right. Unfortunately what the vehicle manufacturer delivers is always a compromise between ride, handling, space and manufacturing cost. This is why many 4WD owners turn to the aftermarket to customise their vehicle to better suit their individual application. The choices are many. Heavier duty springs and shocks for improved load carrying and handling characteristics. Taller suspension components for additional tyre to 'guard and ground clearance. Custom parts for extended wheel travel and articulation. These are some of the modifications owners will initiate to set their 4WD vehicle up to their own specification.
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Words by Mathieu Raudonikis
Your vehicle's suspension is the all-important link between its wheels and tyres and the load-bearing platform, ie: the chassis or monocoque. Its function is not only to provide a smooth ride for the vehicle's load (including the occupants) but to maintain the maximum permissible contact patch between the tyres and the road surface. It does this by absorbing some of the lateral loads placed on the vehicle during manoeuvres.
To absorb these loads the suspension uses a system of springs and dampers placed in between the wheel mounting hubs and the chassis. On 4WD vehicles the springs come in a variety of designs but for the most part they will be either be coil, leaf or torsion bar types. Less common are air bag or air springs but their use is becoming more widespread with the availability of quality kits from the aftermarket.
The dampers, or shock absorbers, are normally a telescopic cartridge that hydraulically displaces oil or gas through an orifice to dampen oscillations in the spring.
The springs and dampers can be set up under the vehicle a number of ways but basically they all do the same thing. Traditionally most 4WD vehicles use a 'live-axle' suspension set-up. This is where the entire axle assembly including the differential, its housing, the axles, hubs, brakes, wheels and tyres are all suspended away from the chassis. This robust system is great for 4WDs and heavy vehicles as it delivers long wheel travel and the differential housing protects many of the axle components from road damage. Its shortcomings however, are that because the wheels on either side of the axle are linked by the axle housing they can't act independently of each other and thus when the wheel on one side drops into a pothole or bounces over a bump, an opposing action is transferred to the wheel on the opposite end of the axle, affecting that wheel's contact with the road as well as the wheel that hit the obstacle. Also the high unsprung weight of the axle with the wheels and tyres affects the ride quality and the suspension's ability to keep the tyres on the ground. Examples of 4WDs with live axles both front and rear include Nissan Patrols, Land Rovers and non-IFS Toyota LandCruisers.
read on below advertisement
The alternative to the 'live-axle' design is independent suspension. With this design the differential is mounted directly to the chassis and is connected to the hubs and wheels via constant velocity joints and exposed drive shafts. This allows each wheel to act independently of the other and the unsprung weight is reduced because the diff is now mounted to the chassis and there's no heavy axle housing. The downside of independent suspension is that most designs offer less wheel travel than a live-axle set-up, but the improvements in ride quality and handling far outweigh this. Examples of full independent suspension include the NM Pajero, Toyota RAV4, Hummer and Subaru Forester. Many 4WD vehicles have independent front suspension (IFS) with a live rear axle. These include Holden Jackaroo, Toyota Prado, modern HiLuxes, Nissan Pathfinder and the Lexus LX470.
Whatever set up your vehicle has, be it leaf, coil or torsion bar sprung, dual live-axle, independent front or full four-wheel independent suspension, the vehicle manufacturer has spent millions of dollars and thousands of man-hours designing and manufacturing it to be just right. Unfortunately what the vehicle manufacturer delivers is always a compromise between ride, handling, space and manufacturing cost. This is why many 4WD owners turn to the aftermarket to customise their vehicle to better suit their individual application. The choices are many. Heavier duty springs and shocks for improved load carrying and handling characteristics. Taller suspension components for additional tyre to 'guard and ground clearance. Custom parts for extended wheel travel and articulation. These are some of the modifications owners will initiate to set their 4WD vehicle up to their own specification.
next page »
