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One of the terms car owners hear most often in service conversations, yet understand least, is "suspension and steering assembly". In fact, this isn't the name of a single part; it's the general name given to the entire mechanical system sitting between the vehicle's body and its wheels, which together produce road holding, comfort and steering control. The engine moves the car forward, the brakes stop it; the suspension and steering assembly manages the car's one and only physical relationship with the road. That's why any looseness in this assembly is directly a safety matter.

The core job of the suspension and steering assembly

The suspension and steering assembly has three jobs. The first is pressing the wheels onto the road. The moment a tyre loses contact with the road, neither the brakes nor the steering can do anything. The second is limiting how much of the road surface's imperfections are transmitted to the body, in other words comfort. The third is keeping the wheels at the correct angles in space; the steering going straight and the tyre wearing evenly both depend on this. These three jobs conflict with one another. A very stiff system holds the road well but tires the occupants; a very soft system is comfortable but throws the car about when entering a bend. The setting the manufacturer chooses is their own selected point on this balance. As suspension and steering parts wear, the car quietly drifts away from the point the manufacturer chose.

The main parts and what they do

Spring and shock absorber

The two are often mentioned together but they are not the same thing. The spring carries the vehicle's weight and absorbs impact. The shock absorber, meanwhile, dampens the spring's energy. Without the shock absorber, the car would keep bouncing repeatedly after a bump. The hydraulic fluid inside the shock absorber is forced through small orifices, converting motion into heat; this is what we call damping. A spring lasts a long time unless it breaks, whereas a shock absorber is, by its nature, a wearing part.

Control arm

The control arm is the arm that connects the housing carrying the wheel to the vehicle. While it allows the wheel to move up and down, it prevents it from shifting forwards-backwards and sideways. This is largely where braking and acceleration forces are transferred to the body. The control arm itself is usually a solid metal part; problems generally arise in the bushings and ball joint at its ends.

Ball joint

The ball joint is the spherical joint connecting the control arm to the wheel hub. It needs to allow both the up-down movement of the suspension and the left-right turning of the steering at the same time; that's why it's spherical in shape. It involves a ball rotating within a socket, and this socket is lubricated with grease and protected from the outside by a rubber boot. When the boot tears, grease escapes and water and dust get in, wear accelerates. The ball joint is one of the most safety-critical parts of the suspension and steering assembly; a severely worn ball joint develops play, and if it fails completely, the connection between the wheel and the vehicle is lost.

Tie rod and tie rod end

This is the rod that transmits the turning motion from the steering to the wheel, and the joint at its end. How "precise" the steering feels depends largely on these parts being free of play. Even a small amount of play developing in the tie rod end shows up as wandering in the steering and a constant need to correct course on a straight road. Wheel alignment is also physically carried out by adjusting the length of the tie rods.

Bushings

Bushings are the rubber (in some vehicles, hydraulically filled) bearings that sit between metal parts. Their job is both to allow freedom of movement and to prevent vibration and noise from being transmitted to the body. Being rubber, they harden, crack and tear over time. When a bushing wears out, the part moves more than it should, which produces both noise and misalignment. A surprisingly large proportion of suspension and steering noises originate from a torn or hardened bushing.

Anti-roll bar and anti-roll bar links

The anti-roll bar connects the right and left wheels to each other with a torsion bar. When the car enters a bend and the body leans, this bar twists to limit the lean. The short parts connecting the bar to the wheel side are called anti-roll bar links. Anti-roll bar links are thin, small parts and are among the elements of the suspension and steering assembly that start making noise earliest; they're a well-known source of the light clattering heard on rough roads.

Wheel bearing

This is the bearing that allows the hub to rotate freely. When it wears, it produces a humming-like noise that increases with speed, and the intensity of the noise usually changes when the steering is turned to one side.

Why it needs to be considered as a whole

The parts in the suspension and steering assembly don't work independently of one another. A worn-out bushing places extra load on the ball joint above it. A shock absorber with reduced damping causes the wheel to strike the road harder and the neighbouring parts to wear out faster. Deteriorated geometry wears the tyre unevenly. That's why a good suspension and steering inspection isn't about finding and replacing the single part making the noise; it's about looking at the whole system and understanding where the load is coming from.

The lifespan of suspension and steering parts varies greatly depending on the make, model, vehicle weight and, most of all, the condition of the roads used. For this reason, it wouldn't be right to give a single mileage figure that applies to everyone; the inspection interval in your vehicle's owner's manual is what matters. Still, as a general approach, having the suspension and steering assembly examined visually and checked for play during periodic maintenance is the cheapest way to catch problems while they're still small.

If you're noticing noise, vibration or instability in the steering on your vehicle, you can book an appointment with our service centre for a suspension and steering check.