Besides the engine and transmission, your car's suspension might very well be its most important part. Except, it isn’t a singular component but a combination of springs, bearings, tubes, valves, joints, bushings, linkages, and even fluid, arranged in such a way to ensure the weight of your car is always supported and is pressed onto the road in harmony with its design specification, no matter the driving situation.
It plays an important part in allowing the wheels and tyres to maintain a good contact patch with the road, keeping the vehicle stable on uneven surfaces, making it key to both road holding and safety. A worn-out suspension not only makes the car uncomfortable but raises the risk of you losing control.
Suspension can be a confusing topic in and of itself, but most of us grasp how essential it is in how a car not only operates but feels and behaves, so it follows that it might one day need servicing or even replacing to maintain optimal performance and safety. You might even have thought about a suspension upgrade to improve ride quality or handling - maybe both at the same time. And the effects are sometimes night and day.
After a few years of hard service, any car will inevitably start to feel noticeably more unrefined or even lethargic when it rides over bumps, or perhaps vague and unstable when pitched into a corner. This most likely indicates the need for a new set of shock absorbers (also known as struts or dampers), a component that takes the most punishment outside (apart from tyres) on the road to keep you comfortable inside, and it’s important to have them inspected, rebuilt, or replaced before they become a safety hazard.
What Is A Shock Absorber?
Like spark plugs or an oil sump, shock absorbers also have a very straightforward name that match their function. Put simply, they use hydraulic resistance to absorb (or dampen) the impact - both mild and strong - exerted on the wheel and tyres by the surfaces you drive on.
In most cars, they are composed of a metal cylinder and a valve suspended in hydraulic fluid. This valve moves up and down this tube when a force is exerted upon it, though the fluid prevents any sudden agitation and releases the excess energy as heat.
Over time, and especially with the kind of pothole-infested roads we put up with here, the seals and even the fluid itself starts to wear and break down.
A shock absorber is generally referred to when addressing this singular tube assembly, whereas the term ‘strut’ is usually an abbreviation of the MacPherson strut, named after its inventor, an American automotive engineer, who combined the shock absorber with a coil spring into a single contained unit to save space and reduce complexity, which is why people (often enthusiasts) refer to them as ‘coilovers’.
When Do You Need To Replace Your Shocks?
As a rule of thumb, a worn shock absorber can easily be identified by a simple ‘bounce test’. When the vehicle is stationary, quickly and repeatedly put your weight on one corner of the car near the fender to simulate a bump and push down several times. The vehicle should absorb the compression and return the car to its resting position in one stroke, but if it continues to wobble up and down, you’ve got a problem.
Generally, if you’re observant, you’ll start to notice an issue well before that. Aside from the more subtle indicators, any noises or unusual vibration that might stem from the car’s outer corners is a clear signal that something is wrong. Worse, if you happen to find a viscous fluid on the ground near the tyres or, with the aid of a flashlight, in the cavity behind your brake callipers. Get it checked out immediately.
Of course, this is all relative, and your rate of suspension degradation does depend on your specific conditions and how you treat your car. However, when it is determined that your shock(s) or strut assembly need replacement, it's best not to delay.
The Next Step
Once a bad or worn shock or strut has been identified, you could just have your mechanic replace either the front/rear pair depending on the situation. They are typically sold from the manufacturer in pairs and, like tyres, is highly recommended to install them as a set instead of individually.
Your car might have come from the factory with shocks or struts made by a specific company such as Sachs, KYB, Bilstein, Ohlins, Koni, Fox, TRW, or Delphi, and a 1-to-1 replacement will be the most obvious choice to restore your car’s suspension to a like-new status.
However, a lot of these suspension companies do offer similar OEM-style replacements that might be interchangeable with your car despite its factory shocks coming from another brand. For example, Bilstein offers their entry-level B4 range for most European, American, or Japanese cars that have been configured to maintain stock ride characteristics but might be endowed with superior materials, dynamics, build quality, and reliability - these are claimed by the manufacturer, of course, so choose wisely.
And if you’re looking to upgrade your suspension system in search of dramatically better handling and performance, the majority of these same brands offer a wide range of aftermarket options that include adjustability for ride height, spring preload, camber, and compression/rebound.
Other companies such as KW, ST, BC Racing, Tein, and Fortune Auto focus almost exclusively on high-performance aftermarket suspension and specialised solutions that may or may not be compatible with your car. It’s worth finding out as the effects can be transformational.