Shock absorbers and suspension: spotting wear

Suspension has a job that is often forgotten behind comfort: it keeps the tyres on the road. Grip exists only while a tyre is pressed onto the tarmac under load, and every bump tries to lift it off. Springs carry the weight and absorb impacts, shock absorbers make sure the spring does not keep bouncing afterwards, and arms, joints and rubber bushes hold the wheel in the position the designers intended.

Wear in this system is therefore first of all a safety matter. A wheel that briefly hops after a bump transmits neither braking nor cornering force at that moment. The ABS then works harder, the stopping distance on an uneven road gets longer, and an avoidance manoeuvre gets more unsettled. On a smooth road at a gentle pace you notice little of this — which is exactly why it goes unnoticed for so long.

Potholes and winter are especially hard on suspension. A hard hit can break a spring, knock out a joint or shift the alignment, salt attacks springs and damper bodies, and cold makes rubber bushes hard.

Suspension is made up of parts that wear at different rates and announce themselves in different ways. Some make noises, others only change how the car drives, and some can only be seen from underneath:

The clearest sign of tired dampers is continued bouncing. After a long undulation on a country road the body does not settle after one movement but bobs once or twice more. Under braking the nose dives further, under acceleration the tail squats, and in corners the car leans more than it used to.

Then there are signs that are easily blamed on the road. The car is more sensitive to crosswinds and ruts and needs constant correcting on the motorway. On transverse ridges the wheels hop audibly, the steering wheel vibrates in a certain speed range, and over edges and manhole covers comes a knocking or rattling that was not there before.

Noises can be sorted roughly. A dull knock over bumps points more towards bushes, drop links or damper mounts; a click when steering at a standstill towards top mounts or springs shifting in their seats; a hum that gets louder with speed and changes in corners more towards a wheel bearing than the suspension. Only a lift gives a certain answer.

The old test of pushing a corner of the car down and letting go only finds gross cases; modern dampers can seem fine that way even when worn. More telling is a measurement on a damper test rig, which many workshops have, together with a visual check from below.

Tyres keep a record of the suspension. One pattern is typical of dampers: cupping, shallow dips repeating at regular intervals around the tread. It forms because a poorly damped wheel hops and scrubs harder at the same spots each time. You feel it with a flat hand better than you see it, and you hear it as rolling noise that rises with speed.

Wear on just the inner or outer shoulder, by contrast, points to the axle geometry, which is often knocked out by worn bushes or a hit against a kerb. That is why a new tyre alone does not solve the problem: it develops the same pattern as long as the cause remains. What the other wear patterns say about pressure and care is covered in the article on summer and winter tyres.

After a hard hit in a pothole, then, a close look is worthwhile: a bulge in the sidewall, a dent in the rim, a steering wheel that suddenly sits off-centre, or a car that pulls to one side. Each of those is a reason to go to the workshop, not to wait and see.

Shock absorbers and springs are replaced per axle, left and right together, even if only one is faulty. A new damper next to a worn one makes the axle uneven: the car behaves differently in left and right bends and can pull to one side when braking on a rippled road. The same goes for springs, because a new spring sits at a different height from an aged one. Top mounts and dust protection are sensibly renewed along with the dampers, because the labour is the same.

Then comes the wheel alignment. Any work on springs, dampers, bushes or track rods changes the geometry slightly, and even a small toe deviation wears a tyre down quickly. Ask for the printout before and after adjustment. If a value lies outside the adjustment range, a part is bent and adjustment alone will not help.

Two special cases. Cars with adaptive dampers or air suspension have more expensive parts and often sensors for ride height and headlamp levelling that need to be recalibrated after the work; a workshop that knows the system is worth it here. And anyone fitting sports or lowered suspension needs, depending on the country, an approval or an inspection with an entry in the vehicle papers. Without it the car no longer matches its registration; the country's road traffic or registration authority can tell you what applies.

Suspension can be judged better during a viewing than many think, if you keep to the order. First at a standstill: does the car sit level, or is one corner lower? Shine a torch through the wheel arches onto the springs, especially the lower coils, and look for oil traces on the dampers. Run your hand over the tyres, inside and outside. Then, with the car stationary, turn the steering from lock to lock and listen for clicks.

What you find here and on the drive is rarely a reason not to buy a car, but it is almost always an item for the sum. A set of dampers with an alignment is a plannable expense; suspension that feels suspicious and never gets looked at is not. If you are unsure, a check on a lift at a workshop near the car is the quickest answer. What else counts on a test drive is covered in its own article.

On the drive itself, look specifically for the roads that challenge the suspension: