Knocking over bumps
Where the noise comes from
suspension, the wheel area
Go to the garage without delay
A knock that appears only over bumps — expansion joints, cobbles, speed bumps — almost always comes from the running gear. Going over a bump the suspension compresses and extends, and if play — free movement — has appeared in one of the joints, the part hits its mounting on every stroke. For cars older than five to seven years this is an ordinary story, and it is usually cheap wear parts to blame rather than major assemblies.
The pattern of the knock narrows the list of suspects. Frequent dull tapping on small ripples at the front is the classic anti-roll bar link; the same pattern at the rear means the rear links or the beam bushes — the rubber bushes through which the beam attaches to the body. Single thumps over potholes point to control arm bushes or tired dampers. A separate case is a knock in time with the wheel turning that appeared after a recent tyre change: it may be loose wheel bolts, and that is the version to check first.
Possible causes
| Cause | How likely | Danger |
|---|---|---|
| Anti-roll bar links | Most often — frequent knocking at the front over small bumps | shop this week |
| Rear suspension: rear links, beam bushes | Common — if the knock is at the rear | shop this week |
| Control arm bushes or dampers | Common — single thumps over potholes | shop this week |
| Play in the steering rack | Rarer — the knock comes straight into the steering wheel | shop this week |
| Loose wheel bolts | Rare — but the first thing to check after a tyre change | pull over |
Can you keep driving
With a typical anti-roll bar link or bush knock you can drive: these parts do not fail suddenly, and a week or two before the check changes nothing as long as you take big potholes slowly. The suspension check itself is quick: a mechanic rocks the joints on a lift and finds the play in a few minutes. Dragging it out for months is still a bad idea: a worn joint passes impacts to its neighbours and speeds up their wear.
A rhythmic knock in time with the wheel turning in the first days after a tyre change looks different: that is a reason to stop at the first opportunity and check the bolts on every wheel with the wheel brace. A wheel on loose bolts wears out the holes in the rim and in the worst case can come off while driving. A knock that comes into the steering wheel should not wait either: the steering is a safety system and gets checked within days.
What to check yourself
- If the wheels were recently taken off or swapped, check the bolts on every wheel with the wheel brace first, before any other theory.
- Note the pattern of the knock: frequent tapping on small ripples and single thumps over potholes are different parts, and that detail narrows the mechanic’s search straight away.
- Work out whether the knock is at the front or the rear: drive slowly with the windows down along a wall or fence — the reflected sound is much easier to hear.
- Hold the steering wheel under slight tension on a rough road: if the knock felt in your palms quietens, it looks like play in the steering rack, and that is worth mentioning at the garage.
- Rule out the simple things: take loose items out of the boot, check that the spare and the jack are secured, press on the closed bonnet — a loose bonnet latch taps much like the suspension.
Narrow the cause down with questions
Answer a few questions and the diagnostic tree will shorten the list of causes for your case.
How the app helps
The Pro-Stuk app asks the same questions as this page, only step by step: what kind of knock, where you hear it, how it behaves on different bumps. From your answers and the recording it builds a report with likely causes and an urgency traffic light — with it, deciding between a garage tomorrow and a garage whenever is easier.
Common questions
Why is the knock heard only over bumps and not on a smooth road?
Play in a suspension joint shows up only when the suspension is working: over a bump the part shifts in its mounting and hits. On smooth tarmac the suspension travel is small and the worn joint stays quiet. That is why knocking over bumps is nearly always about the running gear, not the engine.
I had the tyres changed recently and now it knocks. Coincidence?
Probably not. A rhythmic knock or clatter in time with the wheel turning in the first days after the wheels came off is the classic sign of loose bolts. The check takes five minutes: go round every wheel with the wheel brace. After any tyre change it is worth re-torquing the bolts again after 50–100 kilometres.
The anti-roll bar links are knocking. Is that urgent?
The links themselves are not dangerous — they are small rods that wear out first in the suspension, and the car stays controllable with them knocking. But more serious parts can knock in a similar way, so a check within a week or two is needed: on a lift the source is found in minutes.
The app for iPhone and Android
The questionnaire, the sound recording and the full report with probabilities are all in the Pro-Stuk app.
Installed from a store, the app updates itself.