In short. A tire bead leak is usually a wheel problem, not a tyre problem. Dirt and moisture work their way between the tyre bead and the rim's bead seat, the aluminium corrodes, and the rough surface lets air escape slowly over days or weeks; the corrosion cannot be seen until the tyre is off the rim. Confirm it with soapy water or a water tank, then have the tyre removed: a light, measured clean-up of the bead seat and a bead sealer is the repair one car maker publishes, while the European wheel makers' association treats a leak from a worn rim-tyre interface as a reason to replace the wheel. A crack is never repaired.
This guide covers the rim side. For punctures in the tread, valves and normal pressure loss, read our guide to slow punctures.
What the bead seat does
The bead is the edge of the tyre, built around a hoop of steel wire. It sits on the bead seat, the narrow ledge on each side of the rim, and is held sideways by the flange. Just inside the seat is a small ridge, the hump, which stops the bead sliding into the well of the rim; Continental says the rims for tubeless tyres must have humps or ledges. On a tubeless tyre there is no inner tube: the seal is rubber pressed against metal, all the way round, on both sides.
What presses it there is the air. Our calculation for a 225/45 R17 tyre: the ring of sidewall between the rim (431.8 mm across) and the outside of the tyre (634.3 mm) has an area of about 0.170 m². Multiply by the pressure and you get the force pushing outwards on that sidewall:
| Pressure | Push on one sidewall (upper bound) |
|---|---|
| 220 kPa (2.2 bar, 32 psi) | 37.3 kN |
| 250 kPa (2.5 bar, 36 psi) | 42.4 kN |
| 275.8 kPa (40 psi) | 46.8 kN |
It is an upper bound, because the carcass carries part of the load, but it shows the scale: tonnes of force hold a sound bead in place. The US standard FMVSS 109 tests that grip on "a clean, painted test rim": the bead must not unseat below 6,670 N, 8,890 N or 11,120 N depending on section width (S4.2.2.3.1), and FMVSS 139 applies the test to radial light-vehicle tyres (S6.6).
So a bead leak is rarely a bead that has moved. It is a seal that has lost its surface.
What causes a bead leak
General Motors describes the mechanism in a public service bulletin (08-03-10-006I, March 2025, published by NHTSA). Abrasive particles get between the tyre and the wheel at the bead seat. There is always some relative movement between the two when the car is driven, and that movement lets the particles wear both materials. Corrosive media then get into the interface, and "eventually a path for air develops". The customer notices "a tire that slowly loses air pressure over a period of days or weeks". The corrosion can be on the inboard or outboard seat, and it "will not be visible until the tire is dismounted".
Other causes that end in the same symptom:
- Old, rusty or pitted seats. Michelin lists a rim that is "old and rusty" among the reasons a tyre loses pressure faster than normal.
- Rubber deposits and dirt left at the last tyre change. The European Association of Wheel Manufacturers (EUWA) asks that the bead seats of a tubeless rim be "free from rust and rubber deposit, in order to ensure air-sealing" (ES 1.09, 2.4), and Continental says to use only clean, rust-free rims.
- A damaged flange after a kerb or pothole. EUWA lists bent rim flanges among the defects that require replacement.
- A damaged tyre bead from fitting or from running flat. EUWA asks for any tyre and wheel that has run at 80 per cent or less of its recommended pressure to be removed, disassembled and inspected (2.2).
- The wheel itself: porosity in a cast wheel, or a crack. Those leak through the metal, not at the bead, and are covered below.
How to find the leak
With the tyre at normal pressure, brush soapy water on the valve and core, the tread, the line where tyre meets rim, and the wheel face. A leak shows as bubbles that grow. This is common practice rather than a maker's procedure, and it cannot see the inboard bead or the back of the wheel on the car. Do not get under the car to look unless it is raised and resting on axle stands.
A workshop takes the wheel off and uses a water tank. GM's procedure begins with "a water dunk tank leak test" and only then dismounts the tyre if the air comes from around the bead seat.
| Where the bubbles are | What it points to | What decides |
|---|---|---|
| On the tread | A puncture | Whether the tyre is repairable: see plug or patch |
| At the valve core or the base of the valve | The valve, or its seal in the rim | The valve, not the bead: see tyre valve stems |
| Along the line between tyre and flange, in one spot or several | The bead seal: corroded seat, rubber deposit, damaged bead or flange | Tyre off, seat and bead inspected |
| On the wheel face or barrel, away from the bead | Porosity or a crack in the wheel | Inspection by a wheel professional |
| Nowhere, but the pressure still drops | The inboard bead or back of the wheel | Water tank test with the wheel off |
Continental's repair page sorts it the same way: slow leaks from the valve or rim are not a tyre repair, because "the leak is caused by a faulty valve stem or rim corrosion, not by the tire itself".
How a bead seat repair is done
The only written repair procedure we found from a vehicle maker is GM's, for its own aluminium wheels and for trained technicians; the bulletin says it is "NOT" for a do-it-yourselfer. In outline:
- Wheel off, water tank test, tyre dismounted if the leak is at the bead seat.
- Identify the corrosion: it looks like blistering of the wheel finish, a rough or uneven surface the tyre cannot seal on.
- Measure it. Up to 32,186 km (20,000 miles), the total length of repairable corrosion is 100 mm (4 in) or less; beyond that mileage, 200 mm (8 in) or less. Above those lengths, the wheel should be replaced.
- Remove the corrosion and any flaking paint with a fine-cut sanding disc, back to material that is stable and firmly bonded, tapering the paint edges. Remove "ONLY the material required", and keep the sealing surface as smooth and level as possible.
- Coat the area with a commercial bead sealer, a black rubber-like coating that fills and seals the resurfaced seat. At 21 °C (70 °F), GM says it sets enough for mounting in about 10 minutes.
- Remount the tyre and refit the wheel, with the wheel bolts or nuts tightened to the car maker's torque.
GM excludes in-warranty repairs of chromed wheels, where the result is not lastingly cosmetic.
How much is 100 or 200 mm? Less than it sounds. We set the GM limits against the circumference of the bead seat, taken at the nominal rim diameter:
| Rim diameter | Seat circumference | 100 mm is | 200 mm is |
|---|---|---|---|
| 15 in | 1,197 mm (47.1 in) | 8.4% | 16.7% |
| 17 in | 1,357 mm (53.4 in) | 7.4% | 14.7% |
| 18 in | 1,436 mm (56.5 in) | 7.0% | 13.9% |
| 19 in | 1,516 mm (59.7 in) | 6.6% | 13.2% |
| 20 in | 1,596 mm (62.8 in) | 6.3% | 12.5% |
| 21 in | 1,676 mm (66.0 in) | 6.0% | 11.9% |
The real seat diameter differs by a few millimetres, which does not change the picture.
Why the wheel makers are stricter
EUWA, whose members are the main wheel makers for all types of vehicles, publishes service recommendations that cover passenger car wheels, though they are written above all for trucks and buses. It lists among the "typical defects that require the parts replacement" any "leaks in tubeless tyres derived by micro-cracks in the rim or by wear and tear marks on the rim-tyre matching surface". It also writes that repair of a damaged rim "by heating, by welding, by addition or removal of material is absolutely forbidden", and that "if in doubt about the suitability of a wheel/rim component, the involved part must be replaced" (ES 1.09, 2.3). At the same time it allows wire brushes or sand blasting to clean rust and deposits off contact surfaces before mounting (2.4).
The two texts diverge. Brushing off rust and old rubber is cleaning, which both accept; sanding pitted metal back to sound material removes metal, which GM prescribes within limits (its bulletin even says not to replace a wheel that can be repaired within them) and EUWA forbids. We do not settle that for you. What decides is the instruction of your wheel's maker and the judgement of the fitter who has the bare seat in front of them. A diamond-cut or polished wheel adds its own question of finish: see diamond-cut wheel care and corrosion.
Two things the texts agree on. EUWA says do not fit an inner tube to a tubeless tyre to cure an air leak (2.4). And none of the documents we read presents a sealant poured into the tyre through the valve as a fix for a bead seat. The British repair standard, BS AU 159, excludes liquid sealants and externally inserted plugs from its scope, and Victoria's transport department says inflation kits are "typically for emergency use only". The bead sealer in GM's procedure is a different product: it is brushed onto the bare, cleaned seat with the tyre off.
Porous cast wheels
A cast wheel is liquid metal that solidifies in a mould, and it can trap gas. In aluminium castings, hydrogen is "the only gas that dissolves in significant quantity", and in castings of a few kilograms the pores are usually 0.01 to 0.5 mm across (Wikipedia, Casting defect). If pores connect through the wall, air passes, and the bubbles appear on the wheel, away from the bead.
GM sends this case to a separate bulletin (05-03-10-003, repair with adhesive sealant), which we have not read. EUWA replaces a wheel that leaks through micro-cracks, and a pore and a fine crack are hard to tell apart by eye: that call belongs to a professional.
What about forged wheels? General references on forging list a "reduced chance of voids" among the advantages of open-die forging; we found no measurement of porosity in forged car wheels, so we draw no conclusion from it. A forged wheel's bead seat can still corrode, collect deposits or crack after a hard impact. The differences between the processes are in forged, cast and flow-formed wheels.
Repair or replace the wheel
| Finding | What the texts we read say | Outcome |
|---|---|---|
| Rust or rubber deposit on the seat | EUWA and Continental: seats clean and rust-free before mounting | Clean, remount, test |
| Corrosion pitting within GM's limits | GM: sand and seal; EUWA: no removal of material | Wheel maker's instruction and fitter's judgement |
| Corrosion beyond 100 mm or 200 mm | GM: replace the wheel | Replace |
| Porosity in a cast wheel | GM: adhesive sealant (bulletin not read); EUWA: micro-crack leak means replacement | Professional diagnosis; if in doubt, replace |
| Crack, bent flange | EUWA: no heating, no welding; replace | Replace |
| Damaged tyre bead | USTMA and VicRoads: repairs only in the tread area | New tyre |
If a wheel has kerb damage as well as a leak, our guide to alloy wheel repair explains what can be put right and what cannot.
Refitting: the seating pressure limit
Once the seat is sound, the tyre goes back on with mounting paste on the beads and rim, and is inflated until the beads pop over the humps; the steps are in how to mount a tyre on a rim. This is workshop work: Continental wants the rim secured on the mounting machine during inflation, and a safety cage or other restraint if the machine has none. It gives the limits: in Germany the wdk sets 3.3 bar to get over the hump and 4.0 bar for seating; for the USA and Canada it cites the USTMA at 2.75 bar, 40 psi; for Japan, JATMA at 3.0 bar, 44 psi. It forbids flammable substances to seat a bead and says never to inflate a tyre on a rim lying loose on the floor. In the US, OSHA 29 CFR 1910.177 tells employees to stay out of the trajectory when inflating and says bead seating must not exceed the manufacturer's maximum pressure (g)(10), although the rule itself does not apply to automobile wheels (a).
A bead that will not seat at the limit is not cured with more air: Continental says to reduce the pressure and find the cause. Once seated, the tyre goes down to the pressure the car maker gives.
The rules where you live
None of these countries has a rule about bead leaks as such, but each has texts that catch the results.
| Country | What applies | What it says |
|---|---|---|
| United Kingdom | MOT inspection manual, section 5.2 (DVSA, updated 14 October 2026) | A tyre incorrectly seated on the rim: major, 5.2.3(k). Tyre obviously under-inflated: minor, 5.2.3(l). TPMS malfunctioning or obviously not working: major, 5.2.3(h). Any fracture or welding defect on a wheel: dangerous, 5.2.2(a) |
| United Kingdom | BS AU 159 (tyre repairs) | Covers tyres and valves; plugs inserted from outside and liquid sealants are outside its scope; it says nothing about the rim |
| United States | FMVSS 109 and 139; OSHA 1910.177 | Bead unseating test for new tyres; workshop safety for truck wheels. Periodic inspection, where it exists, is set by each state: we have not read the state rules |
| Australia (Victoria) | VicRoads, Vehicle Standards Information 16 (October 2021) | "Repairs are not permitted in the bead, sidewall or shoulder area of the tyre"; the tyre must be removed from the rim for a permanent repair. Other states publish their own sheets, not read here |
| Canada (Ontario) | MTO Passenger / Light-Duty Vehicle Inspection Standard, section 9 | Reject if a "leaking tire will not maintain a constant air pressure"; reject a wheel or rim that is damaged, cracked or distorted, or welded or repaired in a way that does not meet industry standard. Other provinces not read |
If the pressure warning keeps coming back, our TPMS guide separates a low-pressure warning from a system fault. Top up to the car maker's pressure, on the door-pillar label or in the handbook, and have the wheel checked before a long trip.
Frequently asked questions
What causes a bead leak on a tyre?
Most often corrosion of the rim's bead seat: grit and moisture get between bead and rim, wear the surface and open a path for air. Rubber deposits from a previous fitting, a bent flange, a damaged tyre bead and, on cast wheels, porosity in the metal cause the same slow loss.
How do I know it is the bead and not a puncture?
Brush soapy water on the tread, the valve and the line where tyre meets rim, with the tyre at normal pressure. Bubbles along that line point to the bead; bubbles on the tread to a puncture. If nothing shows, the leak may be on the inboard side, which needs the wheel off and a water tank.
Can a tyre bead leak be repaired?
Usually, if the seat is only dirty or lightly corroded. The tyre comes off, the seat is cleaned, and in GM's procedure, corrosion up to 100 mm (200 mm past 20,000 miles) is sanded back and sealed with bead sealer. EUWA forbids removing metal and replaces a wheel whose rim-tyre surface is worn, so the wheel maker's instruction decides.
Does tyre bead sealer work?
In GM's bulletin it is part of the repair: a rubber-like coating brushed onto the cleaned, resurfaced seat with the tyre off, then left to set for about 10 minutes at 21 °C. It is not a liquid poured into the tyre, and it does not fix a crack.
Will a can of puncture sealant stop a bead leak?
None of the texts we read says so. Those products are made for tread punctures; BS AU 159 excludes liquid sealants from repairs, and Victoria's transport department treats inflation kits as an emergency measure.
Is it safe to drive with a slow bead leak?
No text we read gives a distance. Our reading: kept at the car maker's pressure and checked often, a leak that takes days to show is a reason to book the wheel in soon, not to keep topping up for months, because the tyre runs under-inflated between top-ups, and EUWA asks for any tyre run at 80 per cent or less of its pressure to be taken off and inspected. If the pressure drops quickly or a crack is visible, do not drive on it: fit the spare, or have the car recovered, and have the wheel checked before you set off again.
Why does my new tyre leak at the bead?
The tyre is new but the rim is not. A corroded or dirty seat leaks with a new bead as it did with the old one, which is why EUWA asks for bead seats to be free of rust and rubber deposits before mounting.
Where to go next
If the leak turns out to be in the tread, see plug or patch repairs; for corrosion on the face of a wheel, removing oxidation from aluminium wheels and diamond-cut wheel care. If a wheel has to be replaced, the replacement takes the dimensions your car maker gives: Onyx Forged does not recommend a size or an offset. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards; the catalogue shows the designs.
Sources
- General Motors, bulletin 08-03-10-006I, March 2025, published by NHTSA.
- EUWA, ES 1.09, Safety and service recommendations for wheels, sections 2.2 to 2.4.
- Continental, tyre mounting safety instructions (in German; our translation) and Tire repair.
- Michelin, Tyre pressure for cars.
- OSHA, 29 CFR 1910.177.
- eCFR, FMVSS No. 109 and FMVSS No. 139.
- USTMA, Tire repair basics.
- GOV.UK, MOT inspection manual, section 5, updated 14 October 2026.
- BSI, BS AU 159G:2013, scope; Pirelli UK, Tyre puncture repair.
- Department of Transport Victoria, Vehicle Standards Information 16, October 2021.
- Ontario Ministry of Transportation, Passenger / Light-Duty Vehicle Inspection Standard, section 9.
- Wikipedia, Casting defect and Forging.
All pages were read on 16 October 2026.
The Onyx Forged design office.