Suspension – Choosing the right suspension for your touring 4WD vehicle. Offroad Suspension from Ironman 4×4 – Why Foam Cell shocks should be your first choice for serious off road suspension. ABE and TUV Approved
Everyone knows one of the first essential off-road modifications is suspension, but it’s tough to figure out which of the many designs is the best for 4WD touring. TWIN-TUBE, MONO, REMOTE there are so many shock absorber options it’s hard to know which way to look. Each of these designs have pros and cons, but what we’re talking about here is not circuit racing, not rally driving, not desert racing buggies and definitely not your Nan’s Volkswagen Beetle. We’re talking about Australian 4WD touring, one of the harshest touring environments in the world.
In short, suspension has two main components; a spring, and a damper which is also known as a shock. The spring is usually a leaf, coil or torsion bar. It sets the ride height, carries the weight of the vehicle and does a fair bit of absorbing some of the shock when a car goes over anything other than flat ground, or when there’s weight shift as the vehicle is cornering, braking or accelerating.
Let’s back up a bit and take a look at why high-performance off-road shocks exist and how they work, and then you can see how the different designs stack up. When a spring extends after compression it oscillates like a rubber ball bouncing on concrete and that’s where the shock comes in as it dampens down the oscillation and smoothing out the ride.
Shocks are filled with oil, and have a piston rod which goes down into the shock under compression. That rod takes up room, and as the oil is incompressible, a shock needs something compressible inside it to account for the difference in volume between the rod fully inside the shock and fully outside.
In some cases that’s high-pressure nitrogen gas – hence the term ‘gas shocks’, in other cases it’s a foam cell, hence the term ‘foam cell shock’. Gas shocks can be twin-tube or mono-tube, with the difference being whether the shock has a single tube or an inner and outer tube. Regardless of design, all 4WD shocks face significant durability challenges
When the vehicle bounces up or down it generates kinetic energy, and that energy cannot just disappear, it has to go somewhere or transform as per the laws of physics. In the case of shocks, the energy is transformed into heat, same as when you hit the brakes in your vehicle, the kinetic energy is converted to heat by the brakes. So just as brakes overheat and fail, so too can shocks.
A good off road shock is not only robust enough to handle abuse, and tuned appropriately for the vehicle and its use, but it also needs to be able to get rid of heat faster than it is generated. If it doesn’t, well then the shock heats up and can then fail and then all sorts of bad things happen; for example seals blow, or perhaps the oil inside the shock mixes with the gas which means the shock can’t dampen effectively and that is bad news for your vehicles handling and your safety. So you really do need to avoid your shocks from overheating.
Australian off road tourers operate in about the worst possible environment for shock heating in the world. Firstly, they drive heavy vehicles with lots of accessories, often upgrading the GVM and secondly, they do this in very hot environments. Thirdly, they drive over endless kilometres of corrugations, which involve lots of high-speed up-and-down movements for the damper,and hence generating excessive heat.
And lastly they do all of this for long periods with big days driving heading to remote locations and the last thing you need when hundreds of kilometres from the nearest town is a failed shock. A shock that can get rid of excessive heat is pretty much an essential, and this is why it is important to upgrade your factory suspension for some aftermarket gear which is designed for this sort of challenging work.
So if we need heavy-duty shocks, why not look to motor-sport, and maybe high-speed off road buggies? These specialist off-road racers run flat out over extremely rough tracks, and would have approximately 800mm of wheel travel compared to say 260mm for a Toyota Hilux. And they also typically run remote-reservoir shocks in order to handle the massive amount of heat generated by the suspension.
The concept behind a remote reservoir shock is simple. Remote reservoirs create an additional oil storage unit, the ‘remote reservoir’ so there’s more oil and therefore more of a heat sink. In simple terms all of these design features mean the remote-reservoir shocks are better able to dissipate heat than one without a remote reservoir, so what works on a buggy must work on a touring 4X4, right? Wrong.
Just because something works in motorsport doesn’t mean it works elsewhere, and one example is race brakes which don’t work effectively until very hot, not something you could live with in an urban environment. In the same way, the remote reservoir shock design doesn’t translate to recreational work. Here’s why.
In order for the extra oil in the remote reservoir to do any good, the heat actually needs to get to the reservoir. There are two aspects to this; location and pumping.
With race trucks the reservoir is typically mounted very close to the shock itself, often on top of the main shock in a piggyback configuration. In touring 4X4s, there’s less space so the reservoir is typically mounted up inside the wheel arch, connected by a relatively long tube.
High up in the wheel arch is a really poor place for cooling because there is little or no airflow, plus the fact that the front shocks are also close to the hot engine, unlike the open-air mount on a mid-engined race buggy. You wouldnít mount a radiator away from a cooling airflow, and the same applies to shocks.
Then there is the issue of pumping, oil actually flowing to and from the reservoir. You know how a radiator works in a car – cool fluid is pumped into and around the engine, hot fluid comes back into the radiator where it’s cooled and the cycle continues. That’s also how remote reservoir shocks work, but the pump is the up and down action of the shock.
In the case of your average touring 4WD suspension there is not usually enough pumping action to cycle the oil into the remote reservoir because of the limited suspension travel, and because that range of travel isn’t always used – compare that to a race buggy which has far greater travel and uses more of it.
In short, remote reservoir shocks mean you end up paying a lot of money for marketing hype and theoretical benefits that apply to specialised race vehicles, not your touring 4WD.
So what can be done to handle this problem of heat dissipation? There are designs more suited to the real-world needs of touring off roaders, such as Ironman 4×4’s big-bore Foam Cell Pro shock.
A big-bore shock simply means the diameter of the shock body is as large as it can be, and the reason for that is so it can hold more oil. The greater the volume of oil, the greater the ability of the shock to absorb heat, just like boiling a cupful of water in a kettle is a lot quicker than boiling a full kettle. But that’s only part of the solution. The greater the volume of oil, the greater the ability of the shock to absorb heat.
No shock can absorb all the heat generated by a 4WD, it’s got to be dissipated and here again the foam cell design has an advantage. Earlier on we described the issue every shock has when the piston moves into the body – the oil is incompressible, so something has to compress and expand to account for the piston rod taking up space in the shock. In the case of the foam cell design that’s a layer of Nitrile foam with tiny gas-filled cells in it. When the rod enters the shock body those cells are compressed, when the rod exits the cells expand.
The advantage of the foam cell design compared to a conventional gas shock, either twin or monotube, is better heat dissipation. Thatís because the foam layer floats in the shocks outer chamber, so there’s lots of oil in contact with the entire surface of the outer tube which is ideal for heat dissipation, unlike the gas shock approach which has to sacrifice some oil surface area for the gas. The big-bore design also means a lot of outer surface area as well plenty of oil for a heat sink, and both features are ideal for heat dissipation.
Robustness is taken care of too; the twin-tube design of the foam-cell shock means that if there’s an impact to the outer tube, the inner tube is unaffected so the piston can still move up and down, unlike a relatively vulnerable monotube.
The foam cell is also low-pressure, in contrast to the high-pressure monotube or remote reservoir, so there’s less stress on the seals, and less need to hand over more coin for regular shock servicing. Unlike the remote reservoir, there’s just one part to the foam cell, so it’s not as complicated, less expensive to buy and easier to install than the remote reservoir design.
Kristian Ristell, Ironman 4×4`s Suspension Product Director says that ‘when conceiving the Foam Cell Pro shocks our objective was to make the best 4WD touring shock we could and not to make a specific type of shock’. It was only after we evaluated a range of potential designs we chose foam cell technology. We actually make mono-tube remote reservoir shocks for some of our private label customers, so we are not unfamiliar with nor against the concept, it’s just not the right approach for off-road touring in everyday 4X4 vehicles and we’ve got over 20 years of worldwide suspension experience to back that statement up. The foam cell design is proven to work.
Ironman 4×4 stress-tested various shocks by subjecting them to increasing loads until they failed through overheating, then they went out to the Australian deserts and ran tests to see what temperatures were generated in real-world conditions by a variety of 4WD touring vehicles. The Foam Cell Pro ran appreciably cooler than other designs of shocks, never approaching its stress load limit. Have a look at the Ironman 4×4 Foam Cell Pro Torture Test :
‘It’s not just touring 4WDs that have proven foam cell technology’. Kristian says that ‘the foundation of the Foam Cell Pro design concept is proven through our involvement with in the military armouring industry’. What many people don’t know is Ironman 4×4 supplies thousands of suspensions used in heavily armoured vehicles operating in conflict regions around the world such as the Middle East and Africa. That’s a serious business which has no regard for marketing hype or supplying anything which underperforms.’
Ultimately, every shock design is good for a specific purpose. High-pressure monotubes are great for circuit race cars, expensive and bulky remote-reservoirs work on specialist desert racing buggies, and twin-tube gas shocks can be made cheaply which is why you find them on most passenger cars. But the question for most 4WD owners is what’s the best combination of performance, practicality, reliability and robustness for a touring 4WD in real-world off-road touring conditions and that would be a big-bore Foam Cell Pro shock.
Big news for Ironman 4×4 in Europe the Australian company has recently gained formal approval for its range of suspension kits by German TÜV Nord and the German Federal Motor Transport Authority (KBA).Ironman 4×4 is the first suspension company in the world to successfully receive this stringent approval for the most popular current model 4×4 pickups. They include the Toyota Hilux, Toyota Prado 150, Isuzu D-Max , Mitsubishi L200 Triton ,Nissan Navara NP300, Ford Ranger, VW Amarok, Mercedes X-Class, FIat Fullback and the Renault Alaskan.
For German customers this means that their 4×4`s can legally install the KBA/ABE certified suspension kit upgrade without requiring annual re-certifcation. For other European 4×4 owners the TÜV Nord approval also allows for legal installation and conformity with all national and international road laws