Air leaking from the tyre valve

You hear a hiss at the valve, or soapy water bubbles there. The leak can be at the valve core (the small spring-loaded insert), through cracks in a rubber valve stem, where the stem seals in the rim (tubeless), or where a tube valve joins the tube. Most valve leaks are cheap to fix.

Is it safe to ride?

Only if the tyre holds pressure long enough for the trip and you check it before each ride. A fast leak is a flat: do not ride.

Quick checks first

• Is the valve cap missing? Dirt in the core makes it leak.
• Does the valve lean to one side (tube tyre)?
• Is the rubber stem cracked when you bend it?
• Did someone just inflate it with a poor chuck that bent the stem?
• Wet the end of the valve with soapy water each time the pressure is checked. A core that leaks in one stem may hold in another.

Diagnose it step by step

1Remove the cap. Put soapy water on the tip. Does it bubble?

• Yes: go to step 2.
• No: go to step 3.

2Tighten the core gently with a core tool. Does it still bubble?

• No: fixed. Fit a cap with a seal.
• Yes: let the air out, fit a new core, reinflate (Check and replace a tyre valve).

3Put soapy water round the base of the valve and bend it gently each way. Bubbles or visible cracks?

• Yes, tubeless rubber valve: the stem is perished or the seal in the rim is poor. Fit a new valve (Check and replace a tyre valve).
• Yes, metal clamp-in valve: tighten the nut gently; if it still leaks, fit a new seal or valve.
• No: go to step 4.

4Tube tyre: is the valve leaning, or does air seem to come from inside the rim at the valve hole?

• Yes: the tube has crept round the rim and torn at the valve base. Fit a new tube (Repair a puncture in an inner tube) and keep pressure correct to stop it creeping again.
• No: the leak may not be the valve. Go to Tyre slowly loses air.

What happens if you ignore it: a leaking valve lets the tyre run low. Low pressure lets a tube creep and tear its valve off, which deflates the tyre suddenly.

Causes, most likely first