Key takeaways
- There are three tyre valve types: rubber snap-in, metal clamp-in, and TPMS valves that carry a pressure sensor inside the wheel.
- A rubber valve bends if you push it sideways. A metal clamp-in valve is rigid, with a nut at its base. A dash that shows each tyre's pressure almost certainly means sensor valves.
- Soapy water finds the leak: bubbles at the tip mean the core, which can be changed with the tyre on; bubbles at the base mean the whole valve, with the tyre unseated.
- Rubber valves are renewed with every new tyre. TPMS valves keep the sensor but get a new seal, nut, nickel-plated core and sealed cap.
- Never swap a TPMS valve for a plain one: on cars first used from 2012 a TPMS fault is a Major MOT defect.
One tyre keeps going soft and there is no nail in it. Or a fitter on the phone asks whether your car has rubber or TPMS valves. Either way, the valve type decides what the fix involves. It also decides whether the tyre has to come off the rim.
The trade splits valves three ways: rubber snap-in, metal clamp-in and TPMS sensor valves. That is a working split rather than a formal standard. A TPMS valve is itself a clamp-in or snap-in stem with a sensor behind it, and Michelin's own guide simply divides valves into rubber and TPMS (Michelin UK). What matters to you is what each type needs when it leaks or when a tyre is changed. It also matters whether the fix can be done with the tyre still on the wheel.
What is inside a tyre valve?
Every car tyre valve has the same three working parts. The stem passes through a hole in the rim and carries the air. Screwed inside it is the valve core, a small spring-loaded check valve. The air line's connector pushes its pin in to let air through, and the tyre's own pressure pushes it shut again. On top sits the cap.
The cap matters more than it looks. Michelin says "a valve must always have a cap to prevent air loss" (Michelin UK). Trade magazine Tomorrow's Technician says the right cap has a rubber seal "to keep out the moisture" (Tomorrow's Technician). The core is what actually holds the air in, and a core that cannot close fully is a slow leak. A missing cap is not an MOT defect on its own, but it is the easiest part of the valve to put right.
What are the three types of tyre valve?
| Valve type | How it seals | Where you find it | What is renewed with a new tyre |
|---|---|---|---|
| Rubber snap-in | Rubber body pulled into the rim hole grips both sides of it | Most everyday cars without direct TPMS | The whole valve |
| Metal clamp-in | Rigid stem held by a nut, sealed by a rubber grommet | Some alloy wheels and performance cars, and many vans on high pressures | Grommet, nut and core; the stem if corroded |
| TPMS sensor valve | Clamp-in or snap-in stem with a sensor fixed inside the rim | Cars with direct tyre pressure monitoring | Seal, nut, core and cap; the sensor stays unless it has failed |
Rubber snap-in valves
A snap-in valve is a metal valve body moulded into a rubber stem. The fitter pulls it through the rim hole from inside the wheel until a groove in the rubber seats around the hole, and the rubber itself becomes the seal. It is the standard fitting on most ordinary wheels without direct TPMS. The weak point is the rubber. Valve maker Schrader-Pacific says its snap-in rubber is made "to resist ozone damage and prevent premature deterioration caused by rim hole compression, heat, and cold" (Schrader-Pacific). Those are the things that age a rubber valve on the car. That is why a rubber valve is replaced every time a new tyre goes on.
Metal clamp-in valves
A clamp-in valve has a solid metal stem pulled tight against the rim by a nut on the outside, with a rubber grommet doing the sealing. It is stiffer than a rubber valve, and you find it on some alloy wheels, some performance cars and many vans. Schrader-Pacific's clamp-in brochure lists its valves for passenger and high-performance cars and for truck, bus and trailer wheels (Schrader-Pacific clamp-in brochure). The stem can outlast a tyre, but the grommet and nut are wearing parts that are renewed when the tyre is changed. A stem that has corroded into the rim is replaced. Metal is not automatically better: a rubber valve is perfectly sound on an everyday wheel as long as it is renewed with each tyre.
TPMS sensor valves
On a car with direct tyre pressure monitoring, each valve stem is attached to a battery-powered sensor inside the rim. TyreSafe, the UK tyre safety charity, says direct systems use "sensors inside each wheel to measure tyre pressure directly". It adds that TPMS batteries "typically last for between 5 and 10 years" (TyreSafe). Many sensor valves have a metal clamp-in stem with a nut; some use a rubber snap-in stem.
The sensor is kept when a tyre is changed, but its sealing parts are not. Sensor parts maker WEGMANN says the "nut, sealing ring, valve core or valve cap" should be replaced whenever a tyre is changed (WEGMANN automotive). TyreSafe notes that many manufacturers recommend renewing the cap and core every time (TyreSafe).
One thing a fitter should never do is swap a sensor valve for a plain one. TyreSafe's TPMS leaflet says the sensor should not be "replaced with a 'standard' non-TPMS type valve" under any circumstances (TyreSafe TPMS leaflet). On a car first used on or after 1 January 2012, that will fail the MOT (DVSA MOT inspection manual).
- Cores: nickel-plated. Many TPMS stems are aluminium. A plain brass core in an aluminium stem sets up galvanic corrosion that thins the stem until it breaks (Tomorrow's Technician). The nickel coating keeps the two metals apart, and TPMS service kits come with nickel-plated cores (WEGMANN).
- Caps: plastic, aluminium or nickel-coated. A chrome or steel cap on an aluminium stem will seize onto it (Underhood Service). Use the sealed cap from the service kit, or a plastic cap.
Cars with indirect TPMS have no sensors in the wheels at all. TyreSafe explains that they use the ABS sensors to monitor wheel rotation and calculate pressure from that (TyreSafe), so their valves are ordinary snap-ins or clamp-ins. Our guide to the tyre pressure warning light covers what the light means on each system.
How can you tell which valve your car has?
Three checks, in this order, tell you which valve you have. None of them needs tools.
- Look at the dashboard. If the car can show the pressure of each tyre individually, it almost certainly has direct TPMS and a sensor valve on each wheel, because indirect systems work pressure out from wheel speed rather than measuring each tyre. If you only ever get a warning light, the handbook says which system the car uses.
- Push the stem gently sideways. If it bends and springs back, it is rubber. If it does not move at all, it is metal.
- Look at the base. A hex nut where the stem meets the rim means a clamp-in valve. On a car with direct TPMS, that is usually the sensor valve.
Why is a valve renewed with every new tyre?
Because it ages alongside the tyre, and once the tyre is fitted the base of the valve is hidden inside the rim where nobody can inspect it. Michelin says valve replacement "is always carried out when you fit a new tyre" (Michelin UK). Reusing an old snap-in valve means trusting years of aged rubber for the life of a new tyre, and if it then leaks, the tyre has to come off again. On a TPMS wheel the same reasoning applies to the seal, nut, core and cap.
How do you know a tyre valve is leaking?
A typical valve job goes like this. One tyre reads low at each weekly check, and there is nothing in the tread. Soapy water on the end of the stem stays flat, but a froth of small bubbles builds at the base. That points to the valve body or its seal, not the core. So the bead is pushed off the rim on that side and a new valve goes in. The wheel is then balanced and checked for leaks before it goes back on.
The usual clue is one tyre that keeps losing pressure with no nail or cut you can find. If you check the pressures weekly, when the tyres are cold, a valve leak shows up as the same tyre being low each time. To find it:
- Take the cap off and brush or spray soapy water over the end of the stem. A steady stream of small bubbles means the core is leaking.
- Wet the base, where the valve meets the rim. Bubbles there mean the valve body or its seal has failed.
- On a rubber valve, put the cap back on and bend the stem gently from side to side. Michelin's test is to listen: if you hear air escaping as it moves, the rubber is porous (Michelin UK).
- Look at the stem itself: splits or cracks in rubber, white or green corrosion on metal, or a cap that is missing or will not unscrew. If a cap on a metal or TPMS stem has seized, do not force it with pliers: the stem can snap and take the sensor with it. Leave it for the fitter, who will renew the stem parts.
If the valve stays dry, the leak is somewhere else, so work through the other causes of a slow puncture. If you find a nail or screw in the tread, that is a puncture repair rather than a valve job. For a proper pressure check, see how to check your tyre pressure.
Core, valve or sensor: what each fix involves
Not every valve fault needs the tyre off. What the fix involves depends on which part has failed: the core, the valve body or seal, or the TPMS sensor.
- The core is leaking: it can be changed with the tyre still on the wheel. The tyre is deflated, the old core is unscrewed with a core tool, a new one goes in and the tyre is reinflated.
- The valve body or its seal is leaking: the whole valve has to be changed. Snap-in and clamp-in valves are fitted from inside the rim, so the tyre bead is pushed off the rim on that side to reach it; that is our tyre valve replacement service. Michelin recommends a professional for this because it needs "accessories and machines" (Michelin UK). The wheel is checked for balance before it goes back on.
- A TPMS sensor has failed: it is changed the same way, then matched to the car. TyreSafe's TPMS leaflet notes that replacement sensors are set up with "specialist diagnostic equipment" (TyreSafe TPMS leaflet). Sensor maker Schrader adds that each car has its own relearn method. It can be a stationary relearn using a TPMS tool at each wheel, an OBD relearn through the diagnostic port, or an automatic relearn that needs a drive for a set time above a minimum speed (Schrader TPMS Solutions).
Is a damaged tyre valve an MOT failure?
It can be. The DVSA MOT inspection manual lists "a tyre valve seriously damaged or misaligned likely to cause sudden deflation of the tyre" as a Dangerous defect. On cars first used on or after 1 January 2012, a tyre pressure monitoring system that is "malfunctioning or obviously not working" is a Major defect (DVSA MOT inspection manual, section 5.2.3). That TPMS check applies to cars, not vans. The manual has no separate defect for a missing cap or a slowly leaking valve, but a tyre that will not hold its pressure is worth fixing well before the test.
Do vans need different tyre valves?
Often, yes. Vans that run high tyre pressures need valves rated for them. Valve maker Schrader-Pacific rates its standard rubber snap-ins to a maximum of 65 psi. Its high-pressure snap-ins are rated to 80 or 100 psi (Schrader-Pacific snap-in valves). It also makes metal clamp-in valves for truck, bus and trailer wheels (Schrader-Pacific clamp-in brochure). So a van can need either a high-pressure snap-in or a clamp-in, depending on the wheel and the pressure in its handbook. If the van needs new tyres as well, see our mobile van tyre fitting.
What a fitter checks, and what to tell us on the phone
At a leaking valve we check five things:
- which part is leaking: the core, the base or the stem;
- which type of valve it is;
- whether the car has direct TPMS, and whether the warning light is on;
- which cap and core are fitted to any aluminium stem;
- the tyre itself, because a valve leak and a puncture can happen together.
When you call, it helps to tell us:
- where the car is parked and which tyre is losing air;
- whether the stem bends or has a nut at the base;
- whether the tyre pressure warning light is on, and whether the dash shows each tyre's pressure;
- whether sealant has been put in the tyre, because it has to be cleaned out before the valve or sensor is worked on;
- whether the car has locking wheel nuts and where the key is, in case the wheel needs to come off.
Need someone to come to you?
A leaking valve does not need a trip to a garage. We do tyre valve replacement where the car is parked, at home, at work or at the kerb. We find the leak, renew the valve, rebalance the wheel on the balancing machine in our van and check the tyre for leaks before we go. If the warning light points to a sensor rather than the valve, we can replace a faulty TPMS sensor on the same visit. If the leak turns out to be a nail, we can repair the puncture too.
We cover London and the surrounding counties 24 hours a day, typically arriving in 30 to 60 minutes, with no out-of-hours surcharge. We work where the car is safely parked, never on a live carriageway or hard shoulder. Call 07717 389637.
Sources
- DVSA / GOV.UK, MOT inspection manual, section 5: axles, wheels, tyres and suspension
- TyreSafe, What is a Tyre Pressure Monitoring System (TPMS)? and TPMS leaflet (PDF)
- Michelin UK, How to replace a tyre valve?
- WEGMANN automotive, TPMS service kit
- Schrader TPMS Solutions, Back to the basics: TPMS relearn procedure fundamentals (archived copy)
- Schrader-Pacific, Snap-in tubeless tire valves (PDF), Clamp-in tire valves and clamp-in valves brochure (PDF)
- Tomorrow's Technician, Galvanic corrosion: the TPMS killer (archived copy)
- Underhood Service, TPMS sensor corrosion: tips to help avoid a snapped stem (archived copy)
How this guide was checked: written by Abed Jabbarkhel, founder and director of Fast Tyre since April 2021 (Companies House), whose vans replace tyre valves and TPMS sensors at the car. Checked against the sources above on 2 October 2026. The Tomorrow's Technician, Underhood Service and Schrader relearn pages block automated requests, so their full text was read from the Internet Archive copies linked above (captured June 2024, June 2025 and May 2025) on the same day. Where no source gives a figure, such as how often seized caps cost a sensor, we do not give one. Photo: Derwin Edwards on Pexels. It shows a decorative metal valve cap; on an aluminium TPMS stem, use the sealed cap from the service kit, or a plastic cap, instead. The valve drawing is Fast Tyre's own sketch.
Frequently asked questions
Schrader. Car and van tyre valves are the Schrader type, with a removable spring-loaded core behind the cap that the air line's connector pushes open. Presta valves are a narrower type used on bicycles.
It depends on which part has failed. A new core or a rubber snap-in valve is a smaller job than a TPMS valve, where the seal, nut, core and cap are renewed, and a failed sensor also needs a new sensor set up for the car. Call us with the car and the symptoms for a quote.
If the dashboard can show each tyre's pressure, the car almost certainly has direct TPMS with a sensor in each wheel. If it only shows a warning light, it may be either, and the handbook says which. Indirect systems use the ABS wheel-speed sensors and have ordinary valves with no sensor inside the wheel.