Captured in a rare moment with their guard down, the shock absorber fraternity have been found to be lying to us 4WDers the whole time – they don’t absorb shocks at all – Shocking! That’s right, its been a sneaky game they have been playing with us, suggesting they are doing all the toil of hard working springs when really they’ve just been riding the waves and soaking up all the glory – Shocking! So here’s the real (Shocking) story from an insider who has spent many years among these bits and pieces and is ready to tell all on how it really works.
The real shock absorber in your 4WD is the spring !!
Bang….. there, I said it. The spring does in fact absorb the shock from bumps to boulders that are imposed upon the wheel on initial contact, and limits the amount of shock passed onto the vehicle frame and its oblivious passengers. Without a spring, as in a solid mounted frame to axle would mean every single pebble would cause unbearable vibrations and jolts through the vehicle at every rotation of the tyre. Ask the developers of the early horse & carts or go-kart racers and they will explain what that feels like. But that’s not to say shock absorbers don’t have a very special task to perform, despite misleading the average wheeler for the last century or so.
See the problem with springs is:
they keep on springing, that is in their very nature. This may sometimes be referred to as oscillations, or if we want to use more big words we can call it periodicity. This is essentially the ongoing undulation of the spring without any form of dampening. This effect can be very easily felt by simply removing the ‘shock absorber’ from your vehicle and driving it (in a safe non-public place) and you will find the vehicle bouncing down the road after any bump is encountered. The only way to control or limit this is through a process called dampening which is what a shock absorber really is, a dampener. We still refer to the horizontal one up front on your steering linkages as a ‘steering dampener’ but for some reason we don’t use ‘spring dampener’ when referring to the four corners of our 4WD’s suspension.
Now to clear up a little bit of myth on leaf springs before we go too far, there is a particular aspect of this spring design which is sometimes misunderstood as self-dampening. This is the theory that the layering and therefore friction between each surface provides an element of dampening. This is not entirely correct as it is actually referred to as stiction. This is where the layered leaf spring blades pressing against each other (but not sliding) will require some threshold of force parallel to the surface of contact in order to overcome static cohesion, hence the use of special coatings and pads to remove some pulsation effect created by stiction and the variability resulting from wet or dry conditions. Most good aftermarket leaf spring manufacturers will coat their blades in a graphite type material and insert anti-friction pads to overcome this issue, although still using some of the inherent friction to assist in the dampening process. This is where valving in a shock absorber is so important because a firm valved shock absorber on a leaf pack with inherent dampening will create a very stiff ride.
So on to shock absorbers as such.
This hard working device is available in a number of construction styles but regardless all serve the very same purpose. The style and features just help the device work better (or worse) in specific conditions in which it is used.
The very early shock absorber was simply a rotating friction disc applied to a leaf spring all the way back in 1906 but a few bone-jarring rides later the simplest form of hydraulic dampener was created around 1912. A great deal of learning, science and engineering has developed since and we are now at the pinnacle of shock absorber development.
Now we can select from mono-tube shocks to the popular twin-tube shocks and right up to triple by-pass remote reservoir shocks, but ultimately they all perform the same basic task. Taking kinetic energy (spring movement) and converting it to heat which is then dissipated to atmosphere. No, this will not cause global warming, but it is why you will find shock absorbers too hot to touch after a few hundred kilometres of riding across our corrugated outback roads.
So let’s look at the basic function of shock absorbers rather quickly so there is a better understanding of what they do and how to choose what is best for you.
As mentioned their basic function is pretty simple but how they do it well is more complicated and relies heavily on quality components to achieve good performance.
The spring moves up or down as it follows the terrain, so the piston assembly inside the shock absorber moves correspondingly whilst pushing oil through a valve body which is made up of spring steel sections and little orifices. This specially designed valve body can be made to react differently to the speed of the piston. The effort required to push this oil through and back creates the dampening effect but in doing so gets the oil very hot. The design type and materials used in the construction of the body then helps that heat dissipate to atmosphere.
The quality of the oil is very important, the construction type of the shock absorber itself also changes the heat dissipation rate, the seal design and quality is vital to holding in the gas and oil, and the welding of eyes and pins is crucial to performance in arduous conditions. There are lots more features that make up a high performance and high quality shock absorber, and the old adage of “you get what you pay for” very much rings true for shock absorbers. However for most 4WDers and tourers travelling Oz with a big van in tow, there’s simply no need to spend a thousand dollars per corner when you can fit out a whole vehicle for almost half that.
It comes down to ‘value for money’ and ‘fit for purpose’. The average 4WDer will never require the high end performance characteristics of a competition level Fox shock, so why bother wasting your money. However most will exceed the performance of some cheap imports that are merely a volume solution to everyday drivers.
A smart 4WDer will seek advice from a trustworthy and competent suspension specialist who will deliver the best value to suit your requirements, and backed with a warranty that stacks up.
So choose wisely, your passengers will thank you for it.