How Car Suspension Works

An eight-step lesson on a 3D model. See how the spring takes the hit, what the piston does in the oil, how the control arms guide the wheel, and where knocks come from.

8 steps
about 6 minutes
rotate the model

Full screen

Step 1

Suspension connects the wheel to the body

The wheels aren't bolted to the body rigidly: otherwise every bump would hit the passengers and throw the car off course. Between wheel and body sits the suspension: springs take the hit, shock absorbers damp the bouncing, control arms guide the wheel up and down, and the anti-roll bar keeps the body from leaning in corners.

Step 2

The spring takes the hit

The wheel hits a bump and moves up, the spring compresses and stores the energy of the impact. The body barely jerks. But the spring damps nothing by itself: as it expands again, it throws the body back up, like a swing.

Step 3

The shock absorber: a piston in oil

A shock absorber is a cylinder filled with oil. On the end of the rod moves a piston with tiny holes: with every movement of the wheel the oil has to squeeze through them. That turns oscillation into heat.

Wheel moves upthe rod enters the body, oil flows through the piston

Resultthe suspension movement is slowed down

The bump stop is a rubber cone on the rod: it softens the blow when the suspension reaches its end of travel.

Step 4

With a shock absorber the body bounces once

The spring stores energy, the shock absorber dissipates it. Without it the body keeps bouncing, and the wheels alternately press on the road and lose contact with it.

A worn shock isn't a "stiff" ride; it's the opposite: the car keeps rocking after bumps, nose-dives under braking, and stopping distances grow.

Step 5

Control arms guide the wheel up and down

Upper and lower armThe lower arm is longer, so the wheel changes its tilt slightly as it moves — the tire grips the road better.

BushingsRubber sleeves where the arms attach to the body. They crack with age.

Ball jointThe joint between the arm and the steering knuckle: the wheel moves up and down and turns on it.

Many cars have no upper arm: the strut does its job. That layout is called MacPherson.

Step 6

The anti-roll bar works by twisting

In a corner the body leans: the outer springs compress, the inner ones extend. The anti-roll bar is a U-shaped springy rod whose ends are connected to the left and right wheels. When one side goes down and the other up, the rod twists and resists the lean.

Step 7

Where knocks come from

Sway bar linksA rattling knock over small bumps — the most common cause. Quick and cheap to replace.
Strut top mountClunks from above over potholes and when turning the wheel at a standstill.
Ball jointA dull "thud" over bumps and play in the wheel. Failure is dangerous: the wheel can collapse.
Control arm bushingsA "mushy" steering feel, pulling to one side, knocking when braking and accelerating.
Tie rod endKnocking in the steering wheel, steering play.

What to read next

Repair guides for your car"Suspension" section — shocks, control arms, ball joints and links Replacing shocks and strutsguides by make How brakes work3D breakdown How an engine works3D breakdown

3D models: Two-lever independent suspension — 33V1; Coilover Shock Absorber Damper — Robert Prispilović (Sketchfab, CC BY 4.0), simplified for the site, with piston and oil added.