We Test The New Ironman 4X4 Foam Cell Pro Shock Absorber
Engines get the glory, but suspension makes or breaks a car.
What’s the first specs you look at on a vehicle? Probably the power and torque. I’ll leave it to another article to explain just how wrong that is, but for the moment let’s get back to the old saying, “power is nothing without control”. These days it’d be a meme, but that doesn’t alter the fundamental truthfulness of the cliche.
So if you want control, suspension is a good place to start for any car and there’s two main aims. You want a good ride (comfort from A to B), and handling (predictable responsiveness to control). Even if you’re not designing a sportscar, a responsive, easily controlled car feels better to drive, is safer and less tiring.
For 4X4s, the list gets a bit longer and more difficult compared to a roadcar. We have an especial need for strength – resistance to damage and impact. Our suspension must also work over a wider range of loads, perhaps from a weight of 2200 to 3200kg. We also need supple, long travel suspension, which doesn’t help with on-road handling as it means extra body roll. And then there’s designing for fade and failure.
To see why that’s a problem let’s recap how suspension works. Basically, the springs (leaf, coil, air, torsion etc) absorb bumps in the road, then shock absorbers dampen out the resulting bounce. There’s lots of different ways to design shock absorbers, but they all work in much the same way as a coffee plunger – a piston is attached to a circular disc with holes in it, and that’s forced through a cylinder containing oil which provides the damping effect through friction. The energy from the bouncing spring to converted to heat which is then dissipated to the atmosphere. But if heat is generated more quickly than can be dissipated, then the shock heats up to the point where the damping no longer works effectively, affecting both ride and handling, leading ultimately to a complete shock failure.
So suspension, especially for 4X4s, is complicated and requires a lot of compromises. Nevertheless, what would you do if you had a clean sheet for a design, the budget to do what you wanted and decades of experience in designing and supplying suspension? You and I can only imagine, but three years ago that was the reality for Ironman 4X4.
The list of objectives was simple; create a new range-topping shock that would be the strongest and toughest on the market, yet follow the Ironman philosophy of “affordable quality”. The result is the Foam Cell Pro, and the concept of a foam cell shock will need some introduction.
A basic problem of shock design is that when the piston goes down into the shock cylinder it takes up space – imagine a cup brimful of water and you put a spoon in, it’ll spill over because liquids tend not to be compressible. You could solve the problem by leaving an air gap, but air heats up easily, mixes with oil (aeration) and that ruins the damping as the valves are designed for oil, not a mix of air and oil.
The way good shocks are designed is typically to use a compressible, but heat-resistant gas such as nitrogen so when the piston goes down, the gas is compressed. Both monotube and twintube shocks work on that same basic principle.
A foam cell shock is a bit different. It is a twin-tube design, but instead of pressurised gas it uses a foam layer made of cells filled with nitrogen which compress when the piston enters the shock cylinder, and decompress when it exits. One advantage of this design is that the oil is spread more evenly around the shock body, as distinct from the gas solution which compresses the gas into a small area of the shock. This means the surface area of the oil against the tube is increased, and so heat dissipation is improved. Another advantage is that there’s no way gas and oil can mix, so aeration cannot happen. On the other hand, as the gas in a non-foam shock heats up it expands. This puts the oil under pressure which raises its boiling point. This cannot happen in a foam cell shock, which is why foam cells are typically larger volume to compensate.
So Ironman were faced with a choice – monotube, twintube, or foam cell. They chose foam cell as it offered a long-travel design, and better heat dissipation (resistance to fade) than conventional twin-tube. But what of foam’s disadvantages? The first one is a myth, and that’s that the foam disintegrates. Ironman have been making foam cell shocks for years and not experienced this problem. If they had, then they’d hardly have been likely to launch their top model as a foam cell. Second one is that once overheated and aerated, foam cell shocks don’t return to normal after they cool. This again is incorrect because unlike a normal twin-tube which has gas atop the oil with no barrier, the gas inside the cells of foam cannot mix with the oil. The foam cells also take up less room inside the shock tube that the gas in a conventional monotube, which means there’s more space for oil and the more oil you have, the cooler the shock runs.
As foam cells are a form of twin-tube, then if the outer tube is damaged (unlikely) the shock still works. That said, a well-made monotube is extremely hard to dent!
One reason not to go for a monotube was cost and longevity – monos have gas under high-pressure, which creates stress for seals and increases manufacturing costs. Yet that high pressure means monos also offer a more precise control of damping than twin tube designs, and there’s just the one set of valves to run through the oil.
A remote-canister shock was a possibility, but quickly discounted as while the design offers the advantage of improving fade resistance through good heat dissipation, it is expensive, can be difficult to package, and the engineers felt that a large-bore foam cell could meet the needs of even heavy-duty recreational users.
So with the basic design of a foam cell locked in, Ironman next looked at how to make the shocks stronger and better. They started with a 3mm steel outer body, added a one-piece mount base, put a 360 degree weld on the eye ring, used a 20mm chrome piston rod and made dual independent seals around the piston. The piston shroud is made of HPDE, a super-tough plastic, and the metal parts are treated electrophoretically (EDP) which is more like a plating process than painting. There’s also a built-in bumpstop where applicable, just in case the shock gets overcompressed, and the oil is a premium-grade Fuchs blend which has a high boiling point and minimal degradation over time.
That took care of strength and durability. The next objective was useful features. Here we find rubber bushings (where the shock connects to the mount points) for good NVH (noise, vibration and harshness). Where the shocks are designed within a coil spring (coilover) then the coil mount is on a threaded spring seat, so you can adjust the ride height of the vehicle easily without needing to change springs. Ironman also claim the threads provide a heatsink effect. The coilovers also feature a rubber rather than metal spring seat cushion, again for NVH purposes.
The shocks are also fully rebuildable, although given their new price I would question the economics vs a new set, and it’s not really a DIY job. Nevertheless, it’s not a bad feature and if just one component did need replacing then that could be handy when travelling.
Then we come to the size. Ironman make much of the size of the Pros, and in general what sells in the 4X4 industry is bigger and stronger. So why is a bigger shock better, is there a downside, and at what point do we stop making shocks larger and larger?
Bigger shocks need less internal pressure to do the same job as thinner shocks (double volume, quarter the pressure), and less pressure means better durability as less stress on the seals. Bigger shocks have more oil volume, and therefore more ability to absorb heat, in the same way lakes take longer to heat up a pond than a lake. There’s also more surface area as the tube is larger, and that helps with heat dissipation. The corresponding disadvantage is that once heated, the shock will take longer to cool, and the physically larger the shock, the heavier it is, and weight is always detrimental to performance, particularly with respect to suspension. And the larger the shock, the less pressure the oil is under so you don’t get an advantage of increasing the oil’s boiling point, which erodes the big shock’s advantage of greater oil volume.
The damping front is interesting. Consider a very thin damper and a very thick one with then compress both by say 30mm. To meet the damping needs of the car both are going to need provide exactly the same resistance and energy absorption, but the larger shock will spread that load over a greater volume of oil using larger or more valves. On the other hand, the thinner shock would be better at fine-grained, precise control because there’s less oil to flow through the valves, the oil would be under higher pressure, and there’s less inertia with smaller components.
For 4X4 applications the tradeoff is clear – we start with vehicles that weigh 2200kg plus on tyres that aren’t exactly sportscar grade, then we add 300-500kg of gear as standard accessories, put in a lift and then fit heavy offroad tyres with large tread blocks. Having very precise shock control after all that is kind of pointless, so we’re better off with the improved fade resistance and plusher ride of big-bore shocks, both of which are actually good for rough-terrain handling and ride.
Of course, bigger is only better to a point because there’s a limit to how big shocks can be made as there’s simple physical size constraints, and at some point the large shock would be so slow-reacting that handling would be compromised as it would still be damping one bounce when the next arrives.
But that’s all theory, and the question is how it stands up in practice. I watched as four shocks – a standard unit, then Ironman’s Nitro Gas, Foam Cell and Foam Cell Pro were put through their paces on a dyno. The Foam Cell Pro took almost four times longer to heat up to 120 degrees C than the OEM equivalent, and it also comfortably bested its two cheaper Ironman stablemates which both lasted more than double the time of the standard shock.
Ultimately, suspension design is a compromise and to get those tricky tradeoffs right you need skill based on experience – and Ironman have plenty of both.
Our First drive of the Foam Cell Pro
My Ranger had a mixed suspension setup – OME lifted springs in the front, and an extra leaf added to the rear with four Bilstein shocks. The result was pretty good, and I’ve been a big fan of Bilstein shocks for quite a while. But I have test work to do, so Ironman replaced all my shocks and springs with their own gear including four Foam Cell Pros.
Now at this point you’re expecting me to gush about how much vastly better it was as soon as I put the car into gear, because that’s what journos do, right? Well, sorry to disappoint. The ride and handling weren’t hugely different, but there were a few small changes. First, Ironman did the lift properly so the driveline vibration on takeoff was pretty much eradicated by correct use of spacers. On the actual driving there was slightly less nosedive under braking, and overall the ride felt slightly plusher, especially over larger bumps –the worse the terrain, the bigger the improvement. The steering was fractionally more sensitive, which I think is due to a slightly taller lift at the front. On fast, bumpy dirt roads the Ranger was able to put all its power to the ground effectively even in 2WD, but it could before so nothing lost or gained. For what it is, the Ranger has handled well at speed on the blacktop and again not much change there other than, when really pushing, a little more roll so I’d still go for the Bilsteins on the smooth stuff. At the other end of the spectrum at very low speeds over large rocks there was less roll and dive, characteristics that will save your sills.
Watch this space for more updates, but in summary, after a couple of thousand kays I have no complaints. Ironman haven’t advanced vehicle handling to a whole new level and it’s doubtful any shock/spring setup could, because while important, there’s only so much suspension can do. Also, to be fair all the good aftermarket manufacturers do a decent job of tuning and to a great degree a “good” tune is personal preference, dependent on your driving style and use.
What Ironman have done very well is move the market forwards by delivering high-quality, strong, well-tuned shocks at a price-point that will worry their premium-priced competition, and for that reason I’d certainly put them on any shortlist.
For more information on Ironman 4×4, visit their website: http://www.ironman4x4.com