Written by the fitting team at 24/7 Mobile Tyre Services, Glasgow. Last reviewed: July 2026.
You know the signature. A fine, steady line of bubbles exactly where the rubber meets the rim. A tyre that drops three or four PSI a week. And absolutely nothing wrong with the tyre itself.
That is a bead leak, and the tyre is almost never the problem. The wheel is — unlike the alignment issue behind cars pulling after new tyres, this one has nothing to do with steering at all.
If you have not confirmed the diagnosis yet, our page on the nine causes of a tyre losing air will get you there first. This page assumes you already know it is the bead and starts from there.
Quick answer: A bead leak means air is escaping between the tyre’s bead and the wheel’s sealing surface. It is usually caused by corrosion, damage or coating on the bead seat. The repair requires the tyre to be dismounted and the bead seat cleaned back to sound metal. Adding sealant through the valve will not fix it.
What the bead seat actually is, and why it fails
Here is the thing most drivers never realise about a tubeless tyre.
The tyre’s bead is a steel cored ring, pulled hard against a machined shelf on the rim by the internal air pressure itself. The seal is rubber against bare metal. There is no gasket. Safe seating relies on getting this right, which is why manufacturer guidance on safe bead seating pressures exists and matters.
That is an elegant design and it works beautifully, with one condition: the metal has to be clean and smooth. Anything sitting between the rubber and the metal, whether that is oxide, dirt, old sealer or paint, becomes a leak path.
Why aluminium specifically? It oxidises readily, and salt accelerates the process considerably. What you end up with is a chalky white deposit and, over time, pitting. Small craters that the rubber physically cannot bridge.
The Scottish part. Gritting runs roughly October to April across Glasgow and the trunk network. Add coastal salt spray for cars kept in Ayr, Troon, Largs or Helensburgh, and cars parked outside through the whole winter.
Bead leaks are not a rare fault here. They are a seasonal one, and this is the region that gets them.
Steel wheels suffer the same problem, it just presents as rust at the seat rather than white oxide. Worth knowing if you run a van or a budget car on steels.
The seven causes of a bead leak
1. Salt corrosion or oxidation. By a long way the most common. White powder, pitted seat, usually worse on the inner face.
2. Coating over the bead seat after a refurbishment. This one produces a genuine “oh, that is why” moment.
When alloys are refurbished, the bead seat should be masked off or machined clean. Plenty of budget alloy wheel refurbishments powder coat or paint straight across it.
The coating then flakes off under the bead pressure, and the wheel starts leaking within months. On a wheel that looks absolutely immaculate.
If you are having wheels refurbished, ask directly whether the bead seat is masked or machined clean. Get it in writing.
3. Kerb or pothole damage. A flat spot or a bent flange means the bead simply cannot make continuous contact around the full circumference. See what to do when a pothole buckles an alloy wheel.
4. A hairline crack at the flange or in the casting. Often completely invisible until the wheel is submerged.
5. A nicked or damaged tyre bead. From careless bar work or a badly set tyre machine. In this case the wheel is fine and the tyre is not.
6. Old residue that was never cleaned off. Hardened bead sealer from a previous repair, rubber deposits from the last tyre, adhesive from stick on balance weights.
7. Casting porosity. Genuinely rare. Usually shows as a leak through the barrel rather than at the bead, and generally means a replacement wheel.
Confirming it is the bead
On the car. Soapy water at correct working pressure, then watch the junction of rim and tyre for at least thirty seconds. A bead leak gives you a slow line of bubbles, not foam.
Turn the wheel. The leak may be sitting at six o’clock where you cannot see it.
Check both sides. The inner bead is the one people miss, and it is usually the worse of the two.
That makes sense when you think about it. The inner face of the wheel takes the salt spray thrown up by the road and never gets cleaned by anybody.
The definitive test is a water bath, with the wheel off the car and pressurised. It is the only way to be certain, and it is what distinguishes a bead leak from a crack in the barrel.
One seasonal pattern worth knowing. Bead leaks often appear or worsen in cold weather, as the rubber stiffens and contact pressure at the seat drops.
A leak that turns up in November on a wheel that was perfectly fine in August fits that pattern exactly.
The correct repair, step by step
This is what a proper bead repair involves. If any of these steps are missing, it is not a repair.
- Dismount the tyre. There is no shortcut here. Anything done with the tyre still on the wheel is not a bead repair.
- Inspect both the wheel and the tyre bead for damage, cracks and distortion.
- Clean the bead seat back to sound, bright metal. Abrasive pad or wire wheel, both seats, working with the seat rather than gouging across it.
The aim is to remove oxide and residue, not to remove metal or reshape the sealing surface.
- Assess what is left. If the pitting is deep enough to catch a fingernail as you draw it across the seat, cleaning alone may not be enough. An honest fitter tells you at this point, not afterwards.
- Bead sealer, applied sparingly and correctly. A thin, even film on a clean seat.
Our position on this is not negotiable: sealer is an aid on a clean surface, not a substitute for cleaning. Slathering it over live corrosion buys a few months and hands the problem back to you in spring.
- New valve, or a new TPMS service kit. Grommet, nut and core, torqued to specification. Doing a proper bead repair and then reusing a five year old valve wastes the whole job. See TPMS sensor replacement.
- Remount with the correct tyre lubricant and seat the beads safely.
Safety note, and we mean it. Bead seating must be done at safe pressures with proper equipment, in line with HSE guidance on safe tyre inflation. Never inflate a tyre beyond the manufacturer’s stated seating pressure to force a stubborn bead to seat. Tyres have exploded doing this and people have been seriously injured. This is not a home job.
- Retest. Water bath, or a thorough soap test at working pressure.
- Rebalance, refit and torque to specification. More on wheel balancing.
What not to do, and why
Tyre sealant through the valve. It does not address corrosion. It coats and can ruin a TPMS sensor. It makes the next dismount a filthy job, and some fitters will refuse the work or charge extra for the cleanup.
Sealant is a delay, not a repair.
Silicone or RTV on the bead seat. It does not bond reliably to an oxidised surface, it is a nightmare to remove afterwards, and it will leak again.
Over inflating to force a bead to seat. See the safety note above.
Welding a cracked road wheel and carrying on. Our position is plain: a crack in a road wheel is a structural failure. Repairs of this kind are specialist work with no guarantee, and for a wheel carrying a car at motorway speeds, replacement is the responsible answer.
Aggressive acid wheel cleaners. They strip the protective finish and accelerate precisely the corrosion causing your leak. That advice costs us nothing and saves you money, which is why it is here.
When the wheel is finished
Most corroded wheels clean up fine. Some do not. Here is where the line sits.
Replace the wheel if you find:
- Pitting deep enough that cleaning leaves a visibly uneven seat
- Any crack, anywhere on the wheel
- A buckle or flat spot at the flange
- Repeated leaks after a correct repair
- Corrosion that has spread across the inner barrel
Your options, with the honest trade offs:
| Option | Cost | Watch out for |
|---|---|---|
| Used OEM wheel | Cheapest | Ask the seller for photos of the bead seat before you buy |
| New OEM wheel | Dearest | Guaranteed fit and finish |
| Refurbishment | Middle | Only worth it if the seat is sound. Specify masking in writing |
| Aftermarket set | Varies | Check load rating, offset and centre bore carefully |
Stopping it happening again
- Wash the wheels through the winter, including the inner faces. Salt sitting on bare alloy for six straight months is the entire mechanism
- Skip acidic cleaners. Use a pH neutral wheel cleaner
- Have the bead seat inspected every time a tyre is changed. That is the one moment the surface is visible, and looking costs nothing
- Deal with kerb damage early rather than living with it
- Put the bead seat masking instruction in writing if you send wheels for refurbishment
- While you’re at it, it’s worth checking tyre age and tread depth too, since both get missed for the same reason: nobody looks
A fitter’s note on the winter pattern
Our bead leak calls arrive in a wave, and it is a predictable one. They start in late October and run through to about March.
The wheels tell the same story every time. White bloom across the inner rim face, the outer face looking fine, and the customer completely baffled because the tyre is barely a year old.
Two of the more memorable ones came off refurbished wheels that looked showroom fresh from the outside. Powder coat straight across both bead seats, flaking away underneath where nobody would ever see it.
Cleaned back to bright metal, resealed properly, new valves, rebalanced. Both held pressure fine afterwards. The customers were more annoyed at the refurbisher than at the wheels, which was fair enough.
FAQs
What does a bead leak sound and look like? Usually silent. What you see is a fine line of slow bubbles where the tyre meets the rim when sprayed with soapy water, and a tyre that loses a few PSI a week without any visible damage.
Can a bead leak be fixed without removing the tyre? No. The sealing surface is underneath the tyre bead. It cannot be inspected or cleaned with the tyre mounted, and anything applied from outside is a temporary mask rather than a repair.
Will tyre sealant fix a bead leak? No. It does not address the corrosion causing the leak, it can foul or ruin a TPMS sensor, and it makes the eventual proper repair messier and more expensive.
How long does a bead leak repair last? On a sound wheel cleaned back to good metal, a correct repair is durable and often lasts the life of the tyre. On a heavily pitted or marginal wheel, it may not, and a fitter should tell you that before doing the work.
Does corrosion on an alloy mean the wheel is scrap? Usually not. Most corroded bead seats clean up perfectly well. Replacement is needed where pitting is deep, where there is a crack or buckle, or where leaks return after a correct repair.
Can you drive with a bead leak? You can, but you should not ignore it. Persistent under inflation overheats the sidewall and causes internal damage that cannot be undone. Keep it at correct pressure and get it repaired.
Why do bead leaks get worse in winter? Two reasons working together. Road salt accelerates the corrosion, and cold rubber stiffens, which reduces the contact pressure of the bead against the seat.
Will a refurbished alloy leak? It can, if the bead seat was coated rather than masked or machined clean during the refurbishment. The coating flakes under the bead and creates a leak path on a wheel that looks perfect.
A bead leak needs the tyre off the wheel
Which is precisely why it suits mobile fitting. The job comes to the car rather than the car going to the job.
We can dismount, clean the bead seat back properly, fit a new valve or sensor kit, reseal, rebalance and torque to specification, at your home or workplace.
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