On a tubeless tyre, the bead (the stiff edge of the tyre) seals against the rim. Air escapes when the bead or the rim's bead seat is dirty, corroded or damaged, the rim edge is dented, or the tyre was not seated properly when fitted. Tube-type tyres do not seal at the bead: on those, the air comes from the tube.
Is it safe to ride?
With care for short trips if the loss is slow and you check pressure before each ride. A bead that loses air fast can let the tyre come off the rim in a corner: do not ride.
Quick checks first
- Is the tyre tubeless? (TUBELESS or TL on the sidewall.)
- Was the tyre fitted or repaired recently?
- Did you hit a pothole or kerb hard?
- Look at the thin moulded line just above the rim on both sides: is it the same height all round?
Diagnose it step by step
1Tube-type tyre?
- Yes: the leak is in the tube or valve. Go to Tyre slowly loses air.
- No: go to step 2.
2Inflate to correct pressure. Spray soapy water along the rim line on both sides, turning the wheel slowly. Do bubbles come from one area or all round?
- One area: go to step 3.
- All round, many small bubbles: the bead seat is probably corroded. Go to step 4.
- None: the leak is elsewhere. Go to Tyre slowly loses air.
3At that area, is the rim edge dented or the rim cracked?
- Yes: go to Rim is dented or cracked. A dented edge can sometimes be dressed by a wheel shop; a crack means a new wheel.
- No: go to step 4.
4Is the moulded line even all round, both sides?
- No: the bead is not fully seated. A tyre shop should deflate, lubricate and reseat it, never above the bead-seating pressure on the tyre.
- Yes: go to step 5.
5Have a tyre shop break the bead and look. What do they find?
- White powdery corrosion or old rubber on an alloy bead seat: they clean it back to bare metal, and refit with lubricant. This fixes most bead leaks.
- Damaged or cut bead on the tyre: Replace a tyre.
- Grit trapped during fitting: clean and refit.
6After repair, does the tyre hold pressure overnight?
- Yes: done. Check weekly.
- No: check runout of the rim (Check a wheel for runout); a bent rim may not seal.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Corroded or dirty alloy bead seat | Bubbles all round, white deposits | Shop cleans seat and refits tyre |
| Bead not fully seated | Uneven moulded line | Shop reseats bead |
| Dented rim edge | Visible dent, bubbles at that point | Wheel shop or new rim (Rim damage) |
| Damaged tyre bead | Cut or torn bead when removed | Replace a tyre |