The nature of 4WD means that the more ground clearance you have, the more varied the ground you can cover. Which is one of the reasons why suspension modifications are usually the first on the list of things to change when you get yourself a new 4WD.
However, as soon as you start to alter the standard suspension settings on your 4WD, you find yourself coming up with different choices you have to make.
For instance, raising your suspension will not only give you better ground clearance – it will also raise the centre of gravity of your 4WD.
And this means the vehicle will tend to have a lot more body roll when cornering, lowering the speeds you can take corners, and also making the ride less comfortable for you and your passengers.
Fitting a stiffer suspension so your 4WD has better off-road grip and load carrying ability can also lead to a worsening in general ride quality.
And so it goes on.
Your vehicle’s suspension is the link between wheels and tyres and the chassis or monocoque.
Its function is not only to provide a smooth ride but to ensure the tyres keep in contact with the road surface, and to do this it uses a system of springs and shock absorbers (dampers) placed between the suspension components and the chassis.
The purpose of the shock absorbers, by the way, is to limit the “bounce” of the springs. If there were no shock absorbers, each time you went over a bump your vehicle would just keep bouncing along like a rubber ball.
The wheels would also bounce – and remember, when they’re bouncing they’re not in contact with the road – and so would your stomach and those of all your passengers!
On 4WDs there are steel springs - coil, leaf or torsion bar - or on the more expensive vehicles, air suspension.
Coil springs allow more wheel travel than the other two types, but need extra links between the axle and the bodywork to ensure the suspension only moves up and down, and not side to side or backwards and forwards.
Leaf springs (these days usually only at the back) are very strong, and locate the axle well in the backwards and forwards plane, but are unsophisticated and give a worse ride than coils. They also limit wheel travel.
Torsion bars are tough, easy to adjust, and don’t take up a lot of vertical space in the vehicle. However, they are prone to losing their “spring” more rapidly than other types, and when they reach their limits, can break instead of just “bottoming”.
Air suspension is just that – air bags are placed between the chassis and the suspension components in place of springs, and perform the same function. This type of suspension is usually allied to a sophisticated pumping system which can lower or raise the suspension as well as making it harder and softer.
SUSPENSION TYPES
There are three main types of suspension.
The first, and most common, is live axle (also called beam axle).
This is where the 4WD has two solid axles, each suspended on its own springs and shock absorbers. There can also be other suspension components such as anti-roll bars (also called stabilisers) and links which help to improve handling and road holding by locating the axles more precisely i.e. by preventing the body just “wobbling about” on the springs.
This type of suspension is preferred by those who want to go into really rough territory, for several reasons.
Firstly, because it has few components, and all of them strong and heavy, it’s more robust.
Secondly, because the whole vehicle lifts when the suspension rides over an object, it ensures that ground clearance remains more constant at all times.
However, the disadvantage is that ride quality is usually not as good as more modern suspensions because of the weight of the unsprung components – the two heavy axles and wheels – which makes it more difficult for the springs and shock absorbers to control them.
It also doesn’t allow as much wheel travel.
Examples of 4WDs with live axles both front and rear include Land Rover Defenders, some Discoverys and early Range Rovers, plus Jeep Wranglers, Nissan Patrols and some Toyota Landcruisers.
The next type of suspension is all-independent.
This is increasingly used in 4WD vehicles, especially the more expensive ones, as well as many “softroaders”, and usually uses coil springs all round, although the more expensive ones also have air suspension.
The 4WD doesn’t have axles as such. Instead each differential is mounted onto the underneath of the body or chassis, and there are drive shafts which are attached by universal joints between the differential and the wheels. The universal joints (also known as constant velocity or CV joints) allow the shafts to move up and down with the suspension, and in front, allow the wheels to turn side to side.
Each wheel has its own suspension, either strut (a combination spring and shock absorber), wishbones, or swing arms, complete with shock absorbers and other links to locate it precisely.
The main benefit of independent suspension is a smoother ride, because there is less “unsprung weight”, because the differential is attached to the body, and as each wheel has the ability to respond to bumps independently without passing shocks on to the other side of the vehicle via a solid axle.
The disadvantage is that because each spring compresses individually as a wheel passes over an object the vehicle doesn’t necessarily lift, so there’s a stronger possibility of the underneath of the vehicle touching the ground or rocks.
Examples of full independent suspension include the Volkswagen Touareg, new Range Rovers and Discovery 3, Mitsubishi Pajero, as well as “softroaders” including the Mercedes ML, BMW X5 and Volvo XC90.
Some of these vehicles have the option of air suspension which can be pumped up to increase wheel travel and thus give the same benefits as a beam axle plus the benefits of all-independent suspension. At a price!
The third option is a combination of live axle at the rear and independent suspension at the front. This is usually found on some 4WD wagons and 4WD utes. This gives them better load carrying ability at the back of the vehicle, and good lift at the back for clearing objects, combined with a smoother ride at the front.
However the front suspension has the same disadvantages as that in a fully independent suspension.
Examples include the Toyota Prado, Nissan Pathfinder, and every one-ton 4WD ute on the market.
Right, you want to change it. But before you do, remember that the vehicle manufacturer has spent millions ensuring that in standard trim it’s perfect for the job it was designed to do.
For instance you might want to fit heavier duty springs and shocks for improved load carrying and handling characteristics.
Or taller suspension components for additional tyre to mudguard and ground clearance.
Or parts which allow more wheel travel and articulation so you can get across ditches and deep holes without your vehicle grounding and getting stuck.
Here are some of the factors you should consider before you start.
Once modified, will your vehicle still be able to perform day to day duties, or will it only be good for weekend 4Wheeling? For instance, will your raised 4WD still fit under your carport, garage roof or local shopping centre car park? Will the kids still be able to climb up to get inside? Will your wife still feel safe driving it?
If you raise the suspension, will it alter the geometry of the suspension and steering components, as well as the drive shafts? Will this result in wheel alignment problems, driveline vibrations, and excessive tyre wear or affect the operation of other suspension components? It’s essential you speak to specialists or other owners who have carried out similar modifications to check what you might expect.
If you want heavy duty springs the first thing you need to determine is just how heavy your vehicle is likely to be. You can then go to your spring manufacturer or suspension supplier, tell him how much ground clearance you want, and he should be able to work out which springs you need. A point to remember when fitting heavy duty springs is that the vehicle will be skittish over holes and corrugations when the vehicle is unladen.
You also have to ensure you get the right shock absorbers to match the new springs. This is most important as the extended and closed lengths of the shocks need to match the extension lengths of the springs, and the valving needs to match the spring rate.