Symptoms
- Knocking sound only when riding over rough terrain
- No noise when pedaling smoothly on flat, smooth ground
- Noise seems to come from the front or rear depending on the bump
- Accessories like a rack or fender rattle along with the frame
Likely causes
- CommonLoose headsetPlay in the headset bearings shows up most clearly when the front wheel hits a bump.
- CommonWorn suspension pivot bearings (full-suspension bikes)Pivot bearings develop play over time and knock under the impact of bumps.
- PossibleLoose rack, fender, or bottle cageAccessory mounting hardware can loosen and rattle specifically over rough terrain.
- PossibleLoose or worn wheel skewer/thru-axleAn improperly secured wheel can shift slightly and knock on impact.
What to do
- Check headset play first by holding the front brake and rocking the bike, since this is one of the most common sources.
- For full-suspension bikes, grab the rear triangle and try to rock it side to side and up and down to feel for pivot play.
- Check that the front and rear wheel skewers or thru-axles are fully secured and tight.
- Inspect and tighten any racks, fenders, or bottle cages, since these are easy to overlook.
- Ride over a curb slowly while listening carefully to help pinpoint whether the noise is from the front or rear of the bike.
- Tighten or service whichever component shows play, working through headset, then wheels, then suspension pivots.
- If the source remains elusive, a bike shop can systematically isolate persistent creaks and knocks.
Tools and parts
- Allen key set
- Torque wrench
Suspension pivot bearing kitSearch: “full suspension mountain bike pivot bearing kit”
When to call a pro
A bike shop can methodically isolate a persistent knock and service worn pivot bearings on full-suspension frames.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.