At higher speed the whole bike slowly snakes or wanders from side to side, often felt through the seat more than the bars. This is slower than a handlebar shake. It usually starts at the back: low rear tyre pressure, a worn rear tyre, a heavy load behind the rider, worn rear shocks, a worn swingarm pivot, or a rear wheel out of line because the chain adjusters were set unevenly. Tight or worn steering bearings and bent parts can also cause it.
Is it safe to ride?
No, not at speed. When it happens, close the throttle smoothly and slow down without braking hard. Ride slowly until the cause is fixed.
Quick checks first
- Check both tyre pressures cold, especially the rear.
- Look at the rear tyre: worn flat in the centre, or near the wear marks?
- Is there a heavy load, top box or passenger?
- Look at the chain adjuster marks on both sides of the swingarm. Are they at the same mark?
- Has a windscreen, top box or luggage been added recently?
Diagnose it step by step
1Are tyre pressures right and the tyres in good condition?
- No: Check tyre pressure and Inspect tyres for wear and damage.
- Yes: go to step 2.
2Does it weave only with a load or passenger?
- Yes: move weight forward and lower, add preload with Adjust rear spring preload, and keep within the bike's load limit.
- No: go to step 3.
3Are both chain adjusters at the same mark, and is the rear wheel in line with the front?
- No: realign with Check and adjust chain slack. The K-Light 125 manual lists uneven chain adjusters as a cause of rear wobble.
- Yes: go to step 4.
4Does the swingarm move sideways at its pivot?
- Yes: do not ride. Check the swingarm pivot and Swingarm moves sideways or has play.
- No: go to step 5.
5Does the rear wheel rock on its axle?
- Yes: Check wheel bearings.
- No: go to step 6.
6Does the rear bounce more than once after a push down, or is a shock leaking?
- Yes: Check the rear shock absorbers.
- No: go to step 7.
7Is the steering tight, notchy, or loose?
- Yes: Check the steering head bearings.
- No: check the forks are equal and straight with Align the front wheel, forks and handlebar. If everything checks good, have a workshop check frame alignment, especially after any crash.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Low rear pressure or worn rear tyre | Gauge; flat centre | Check tyre pressure |
| Heavy or high rear load | Only when loaded | Reduce and move load; add preload |
| Rear wheel out of line | Adjuster marks differ | Check and adjust chain slack |
| Swingarm pivot play | Sideways movement at pivot | Check the swingarm pivot |
| Worn rear shocks | Bounces; leaking | Check the rear shock absorbers |
| Rear wheel bearings | Wheel rocks | Check wheel bearings |
| Steering bearings tight or worn | Notch, stiffness or play | Check the steering head bearings |
| Bent fork, swingarm or frame | After crash; nothing else found | Inspect the frame after a crash |