Why Is My Tyre Losing Pressure Overnight?

All tyres lose a small amount of pressure over time — typically 1 to 2 PSI per month through normal osmosis of air through the rubber compound. This is normal and not a cause for concern, but it does mean monthly pressure checks are important. If you're losing significantly more than 1 to 2 PSI per month, something is wrong.

Losing enough pressure to notice a visibly soft tyre overnight or within a week means you almost certainly have a slow puncture or other leak that needs attention. Don't just keep re-inflating it — find the cause.

The most common cause is a small object — a nail, screw, or piece of glass — embedded in the tread. The object often seals its own hole partially, causing a slow rather than immediate deflation. Run your hand carefully around the tread (never use bare hands on a spinning tyre) to feel for any protrusions.

A faulty or damaged valve stem is another common culprit. The valve core can become loose over time, or the rubber of the valve stem itself can crack and perish. A quick way to check is to apply soapy water to the valve — if you see bubbles, the valve is leaking. Valve stems are cheap and quick to replace.

On older or corroded alloy wheels, air can seep through microscopic pores in the alloy itself — a problem known as wheel porosity. The fix is to have the wheel cleaned and resealed at the bead, where the tyre meets the wheel rim. This is a workshop job — a mobile fitter can reseat the tyre and apply bead sealant.

A bead leak — where the tyre is not seated correctly against the wheel — can also cause slow pressure loss. This can happen after a tyre has been removed and refitted, or after significant wheel damage. If you've recently had a tyre changed and are now losing pressure, a bead leak is a likely cause.