A tyre that’s fine one week and a few psi low the next has a slow puncture, and the frustrating part is that you often can’t see it. Good slow puncture diagnosis is about knowing the handful of places air escapes and testing each one methodically. Do that and you’ll usually find the culprit in your own driveway.

What counts as a slow puncture?

A slow puncture (or slow leak) is any loss of pressure that happens gradually — over days or weeks rather than minutes. All tyres lose a little air naturally, typically a psi or two a month, so topping up occasionally is normal. If you’re adding air every week, or one tyre consistently reads lower than the rest, that’s a leak worth chasing. Keeping an eye on it is easier if you already know how often to check tyre pressures.

The five usual suspects

Nearly every slow leak comes from one of these:

Two of these have their own guides worth a look: bead leaks: why your tyre loses air without a puncture and corroded rims causing air loss.

How to find a slow leak yourself

Work through these in order. You’ll need a spray bottle, dishwashing liquid and water, and a decent pressure gauge.

1. Inflate to the placard pressure first. A leak shows faster in a properly inflated tyre. Set pressures cold, to the figure on your car’s tyre placard.
2. Mix a soapy solution — a good squirt of dishwashing liquid in water — and spray it liberally over the whole tread, working slowly around the circumference. Watch for a growing cluster of bubbles; that’s your leak. Mark it.
3. Spray the valve. Cover the valve stem and its base. Bubbles at the tip often mean a loose or faulty valve core (sometimes just needing tightening); bubbles at the base mean a perished stem that needs replacing.
4. Spray the bead and rim edge on both the front and back of the wheel. Bubbles right where the tyre meets the rim point to a bead leak or rim corrosion rather than a puncture.
5. Still nothing? Try the water bath. If you can safely remove the wheel, submerging it in a tub of water (or having a fitter dunk it) will reveal the finest leaks as a steady stream of bubbles.

If you find a tread object, don’t pull it out on the spot — note where it is and let a fitter assess it against the repair rules, as covered in nail in the tyre: repairable or replace?

What your TPMS is telling you

If your car has a tyre pressure monitoring system, it’s an early-warning tool for slow leaks — a light that keeps returning on the same corner after you top up is a strong hint of a real leak rather than a one-off. But TPMS has limits: some systems only warn once pressure drops well below target, and sensors themselves can fail. Our guide to how TPMS works and when it lies explains what to trust. Whatever the dash says, verify with a gauge, because running underinflated quietly wears tyres and burns fuel.

Habits that stop slow leaks becoming flats

A little routine catches most slow punctures before they strand you. Check all four tyres (and the spare) cold once a month and before any long trip, and log the readings on your phone so a single low tyre stands out from a general drop. Keep valve caps fitted — they keep grit out of the valve core, one of the most common slow-leak sources. Give tyres a quick visual for embedded objects after driving on building-site roads, gravel or freshly chipped surfaces, which is where thorns, screws and wire tend to lodge. And treat a wheel that has copped a heavy kerb or pothole hit with suspicion, since a hairline rim crack or a bent bead seat can weep air for weeks before you notice.

When to see a fitter

See a tyre shop if you can’t find the leak, if it’s at the bead or rim, or if the object is anywhere near the shoulder or sidewall. A workshop can demount the tyre, inspect the inside and reseal or repair properly — and confirm whether the puncture even sits in a repairable spot. That question is answered in where a tyre can legally be repaired in Australia. And don’t forget your spare can develop a slow leak too — the spare tyre pressure is the one everyone overlooks until they need it.

Frequently asked questions

How much pressure loss is a slow puncture?

Losing more than a couple of psi a week, or one tyre always reading lower than the others, suggests a leak. A psi or two a month across all four is normal.

Can I keep driving with a slow puncture?

Short term, if you keep it inflated to the placard pressure and check it often. But get it diagnosed promptly — running low damages the tyre and a slow leak can suddenly become a fast one.

Will soapy water damage my tyre or wheel?

No. A mild dishwashing-liquid solution is harmless; just rinse alloy wheels afterwards so no residue is left on the finish.

Why does my tyre lose air only in cold weather?

Air contracts as it cools, so pressures read lower on cold mornings without any leak at all. If it’s the same tyre losing air regardless of temperature, that’s a genuine slow puncture.

Bottom line: Inflate to the placard pressure, then spray soapy water over the tread, valve and bead to find the bubbles. Most slow punctures are a small tread object, a tired valve, a bead leak or a corroded rim — all cheap to fix if you catch them early.

Guidance current as of 2026. Have punctures and rim damage assessed by a qualified tyre fitter, and confirm any repair against the rules for your tyre and state.