First, a disclaimer: I am not, by any measure, an expert on vehicle suspension. I have just been fortunate to have been a motoring journalist who had the opportunity to get up close and personal with some people who were professionals in the field, and who had been generous in sharing their knowledge.
Along the way, I have visited several facilities used to develop and manufacture suspension components such as coil and leaf springs and shock absorbers, and have personally used several types of systems in differing conditions, and the experiences have shaped my views, along with additional reading material readily available on the web if you know what you are looking for.
The first factor that affects a suspension system is weight. How heavy a load is expected to be carried by the front axle, and also the rear axle, is what an engineer needs to know.
Knowing the weight that must be borne will yield the strength of the spring, measured as the force (or weight) required to compress said spring by a certain amount. Such as newtons (or kilograms) per centimetre, or pounds per inch.
Then it starts getting complicated. Vehicle weight may vary because we, the users, add stuff to it. The front end load of a typical car will not vary much but the rear will , depending on how much load is carried, where in people or their belongings, or just junk.
Engineers have a particular headache with pick-up trucks because they have to be sprung softly enough to be driven around empty, and also stiffly enough to be laden with an extra thousand kilograms, all of it on the rear axle. So, it is only logical that a pick-up that is comfortable to drive around like a car will sag in the rear end when laden with goods, as pick-uos are intended to. Conversely, one that carries a full load comfortably will be harsh when empty. There is no getting away from the numbers.
On top of that, many buyers also use their pick-ups for adventurous trips into the great outdoors, and decide they need beefier protection in the form of stronger (hence, heavier) bumpers/bullbars, and maybe a winch to add progress through the rough stuff.
That adds around 70 to 90 kilograms on the front axle. It's like having a stout friend sitting on your bonnet. That is why a vehicle that was behaving nicely over bumps and ruts can suddenly feel wallowy after you have stopped feeling pleased with how great it looks with your new bullbar and winch.
The springs are the first line of defence against shocks. They absorb the often violent forces of hitting anything other than smooth pavement at considerably speed.
The problem is that the springs absorb plenty of energy, which must than be dissipated by oscillating. In layman's terms, that is the boing-boing-boing effect. The spring continues to alternately compress and extend for some time after the bump is passed.
|Not sure if they came with car from factory, but still looking pretty good.|
That's where the shock absorbers come in, although the term is debatable since the springs actually absorb the firat shock, and the “absorber” then dampens the oscillations. But if you consider that the damping action is also “absorbing” the residual enery of the boinging spring, then it's all good. So, we'll accept them as absorbers even if some people insist they are really dampers.
The absorbers have to be engineered with the correct damping rates to work with the springs. And there are two rates to be considered, one being compression damping, and the other, rebound damping.
To add more complexity, some springs and absorbers are designed to act progressively, i.e., they get firmer the more they are compressed or pushed, so they do not have a single, linear rate.
Some shocks that are optimised for comfort offer very resistance to compression. When hitting a bump, the shock energy is absorbed entirely by the spring and the absorber compresses easily. But when the spring rebounds, the absorber does its darnest best to slow it down. If all works according to plan, you get one compression of the spring upon hitting the bump, and one controlled rebound or extension to original height, and the drama ends there, allowing a smooth journey to resume, until the next bump or porthole.
That's the short version. The long version is a lot more complicated with many types of spring and damper materials and designs, and electronic wizardry thrown into the mix. I won't go there, but you can read more online. Just ask google.
We've come this far because I have just had a pair of tired old absorbers replaced on a recently-acquired Ford Everest 3.0l, which has been on the road 10 years, and covered just over 200,000 kilometres, and a friend asked for a review of the brand spanking new Old Man Emu Nitrocharger Front Sport Shocks, part number #60222.
What I will say is they are money well spent. That is the because the shocks that came with the secondhand car were well past their prime. I have no way of knowing if they had been replaced at some point or other in the car's previous career, but they were original Ford-issued shocks, embossed with FoMoCo (for Ford Motor Company). So, they could well have been 200,000km old!
Of course, new OMEs, or any new shocks, will yield an improvement. Before the renewal of shocks, the car felt floaty at speed, and the 3.0l common rail engine is capable of getting it up to a decent clip in a quick time.
But the story did not end there. The front torsion bars also seemed to have sagged significantly, to such an extent that there was hardly any room for upward travel before the arms hit the bump stop.
The good news is that torsion bar-type suspension can be easily adjusted, and should have been done earlier. But, better late than never, so they were adjusted at the same time the Emus were fitted, so that now there is ample upward and downward travel.
Also, a clunking noise when going over bumps was traced to a worn out steering idler arm, which was promptly replaced. This immediately yielded a much more precise and controlled dteering feel, which added to the improvement in handling.
In summary, a pair of new front Old Man Emus (note that nothing has been done yet to the rear end, which are still held up by original leaf springs and, yes, a pair of FoMoCo shocks), a slight tweaking of the original Ford-issued torsion bars to raise ride height by some 20mm, and a tight new idler arm to replace the knackered old one, has TRANSFORMED the car.
It handles and rides beautifully now, even with more improvements due to come.
I have not yet renewed any of the many suspension arm bushes, anti-roll bar bushes, etc, that will be on the to-do list in future in the quest to restore that new-car feel.
|Knackered steering idler arm.|
One thing I feel that OME is doing right, and a reson why I like the brand, is that they do not offer a one-size-fit-all solution, such as a “Ford Ranger shock absorber”. Their website http://www.oldmanemu.com.au/ offers a Suspension Selector which asks what front bumper your car has, whether it has a winch, and also what weight is regularly carried in the back, and a specific model of springs and shock absorbers will be recommended for YOUR usage.
It helps to know background information about your vehicle, such as the fact that the Everest, model code U268, was not sold in Australia, but it shares the exact same underpinnings as the Ranger J97 (often erroneously called the T5) so you know which model to look for in the selector.
By the way, I have had these OME shocks for too short a period to give an in-depth review so in no way am I suggesting they are "the best", or even better than other competitors out there. For the record, I have been using a combination of King springs and Koni shocks for my other 4X4s, all of which are Land Rovers, and have been satisfied with their performance and durability.
Oh, I have fitted a brand new set of the latest Michelin LTX Force, size 265/70 R 16, and they are awesome.
|Good tyres are an important part of the ride, and Michelin's LTX Force are very good.|