After a bump the rear of the bike goes up and down several times instead of settling at once. The rear may feel floaty or wallow in corners, and the rear wheel may skip on rough roads under braking. A shock absorber has two jobs: the spring carries the weight, and the damper (oil forced through small holes inside) stops the spring bouncing. When the damper wears out or loses its oil, the spring is free to bounce. On most commuter bikes the shock is sealed and is replaced, not repaired.
Is it safe to ride?
Ride with care. A bouncing rear loses grip on bumpy roads and when braking, and can make the bike weave. Slow down until fixed.
Quick checks first
- Push down hard on the seat and let go. Does the rear come up once and stop, or bounce?
- Look for oil on the shock bodies.
- Check rear tyre pressure (K-Light 125: 210 ± 10 kPa cold).
- Twin shocks: are both on the same preload step?
Diagnose it step by step
1Is the rear tyre pressure correct?
- No: set it with Check tyre pressure. An over-inflated tyre bounces too.
- Yes: go to step 2.
2Does the rear bounce more than once in the bounce test?
- Yes: go to step 3.
- No: the shocks are probably fine; the feeling may be a loose swingarm. Go to step 5.
3Is a shock leaking oil, or is its rod rusty or bent?
- Yes: replace the shock. On twin shocks, replace both. See Oil leaking from a rear shock.
- No: go to step 4.
4Twin shocks: are both on the same preload step?
- No: set them equal with Adjust rear spring preload, then test again.
- Yes: the damping is worn out inside, even without a visible leak. Replace the shocks after confirming with Check the rear shock absorbers.
5Does the rear move sideways at the swingarm pivot?
- Yes: Check the swingarm pivot.
- No: check sag with Measure suspension sag. A very tired spring on a heavily loaded bike can also feel bouncy.
Buying replacement shocks: match the eye-to-eye length (centre of top mount to centre of bottom mount), mount type and spring rate for your bike. A longer or shorter shock changes how the bike steers.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Worn damper | Bounces more than once | Replace shock(s): Check the rear shock absorbers |
| Leaking shock | Oil on body | Replace shock(s) |
| Unequal preload (twin shocks) | Different steps | Adjust rear spring preload |
| Tyre pressure too high | Gauge reading | Check tyre pressure |
| Swingarm play | Sideways movement | Check the swingarm pivot |
Reference values (K-Light 125)
| Item | Value | Source |
|---|---|---|
| Rear tyre cold pressure | 210 ± 10 kPa | K-Light 125 manual, PDF p. 71 |