A hard hit on a pothole, kerb or speed bump can dent the edge of the rim, bend it, or crack it. Cast alloy wheels can crack between the spokes or at the rim edge; steel spoked rims usually dent or bend. A damaged rim can lose air, unbalance the wheel, and a cracked wheel can break apart.
Is it safe to ride?
No if there is any crack, or if the dent is large enough to make the tyre lose air or the wheel wobble. A small cosmetic scrape on the outer face is not a dent.
Quick checks first
- Clean the rim and look closely, inside and outside, with a torch.
- Check the edge where the tyre sits: flat spots or bends.
- Cast wheels: look between spokes and around the hub for fine lines.
- Spin the wheel: wobble or bump?
Diagnose it step by step
1Is there a crack anywhere (a fine line that does not wipe off, often with grey dust or air bubbles)?
- Yes: do not ride. The wheel or rim must be replaced. Cracked cast wheels must not be welded for road use.
- Not sure: spray soapy water with the tyre inflated; bubbles from a line mean a crack. Ask a wheel shop to dye-test it.
- No: go to step 2.
2Is there a dent in the rim edge where the tyre bead sits?
- Yes: go to step 3.
- No: go to step 4.
3Does the tyre lose air at the dent, or is the dent deeper than a scrape?
- Yes: a wheel shop can sometimes dress a small dent on a steel or alloy rim; a large dent means a new rim or wheel. Fit a new tyre if the bead was also cut (Inspect tyres).
- No: monitor. Check pressure every ride for a week.
4. Measure runout (Check a wheel for runout). Over the limit? (K-Light 125: 2.0 mm lateral and radial.)
- No: the rim is serviceable. Check the tyre too (Tyre has a bulge or cut).
- Yes, spoked wheel: if the rim is not dented, it may true up with the spokes (Check and tighten spokes). If it is bent, it needs a new rim and respoking.
- Yes, cast wheel: replace the wheel. Do not heat or hammer it straight.
5Was the hit hard enough to affect the fork, steering or axle?
- Yes: see The bike has been dropped or crashed.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Pothole or kerb hit with low pressure | Dent at bead edge | Wheel shop or new rim |
| Bent spoked rim | Runout over limit, tight spokes | New rim, respoke |
| Cracked cast wheel | Fine line, bubbles | New wheel |
| Corrosion at bead seat | White deposits, bead leak | Clean seat (Bead leak) |
Reference values (K-Light 125)
| Item | Value | Source |
|---|---|---|
| Rim size front / rear | 1.85 × 17 / 3.00 × 15 aluminium | K-Light 125 manual, PDF p. 72 |
| Rim runout limit | 2.0 mm lateral and radial | K-Light 125 manual, PDF pp. 137, 161 |