The valve is the small stem poking through the wheel that the air goes in through. It is easy to ignore, but it is the only opening in an otherwise sealed tyre, so when it fails, the tyre goes down.
How the valve works
Inside the valve is a spring-loaded core, the same Schrader design used on a bicycle. It stays shut to hold the air in, and opens only when a pump or pressure gauge presses on the pin in the centre. That core is what keeps the air where it should be between top-ups.
Most cars use a simple rubber valve that snaps into the wheel. Performance cars and those with pressure sensors often use a metal clamp-in valve instead.
What the cap is for
The valve cap is not just a finishing touch. It does two useful jobs:
- Keeps dirt and moisture out of the valve core, which protects the seal and stops grit working in
- Acts as a second seal, a back-up barrier against a slow leak past a tired core
A missing cap is worth replacing, they cost next to nothing, and the valve lasts longer with one fitted. On metal valves, a plastic cap can be the better choice, as a metal cap can corrode onto a metal valve and seize.
Why valves are replaced with tyres
A rubber valve perishes with age just as the tyre does. After several years it can harden and crack, and a perished valve is a common cause of a slow puncture that has nothing to do with the tyre itself. For that reason, the valve is normally replaced as standard whenever a new tyre is fitted, so a fresh valve matches the life of the fresh tyre, fitted as part of the job whenever a new set goes on, a set ordered from an online tyre seller like Tyres.co.uk included.
TPMS valves are a special case. On cars with a direct monitoring system, the valve carries the sensor and is a metal item with a service kit, the seal, core and cap, that is renewed at fitting to keep it sealing without disturbing the sensor.
From the workshop: a tyre that loses a few PSI a month with no sign of a puncture is very often the valve, not the tyre. It is a cheap part, which is why we just fit a new one with every tyre rather than gamble on the old one.
Sources and accuracy. The valve and cap details here reflect manufacturer and fitting practice at the time of writing. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What does a tyre valve do?+
It lets air in when inflating and seals it inside the rest of the time. A small spring-loaded core in the valve holds the air, opening only when a pump or gauge presses on it. It is a small part, but a faulty one can let a tyre slowly deflate.
Do tyre valve caps matter?+
Yes, more than they look. The cap keeps dirt and moisture out of the valve core, which protects the seal, and acts as a second barrier against slow leaks. A missing cap is worth replacing, they are cheap, and the core lasts longer with one fitted.
How long do tyre valves last?+
Rubber valves perish over time, like the tyre itself, and can start to crack and leak after several years. Because of this, the valves are normally replaced as a matter of course whenever new tyres are fitted, so they match the life of the tyre.
Are TPMS valves different?+
Yes. On cars with a direct pressure monitoring system, the valve is usually a metal one with the sensor built in. These are more expensive and have service kits, seals and cores, that are replaced when tyres are changed to keep them sealing properly.