Why does my tyre keep losing pressure?
7 min readBy Wheel Fit
The short answer Every tyre loses a small amount of air naturally — roughly 1 to 2 PSI a month. Losing several PSI a week is a fault. The cause is a nail in the tread about as often as it is a corroded wheel rim or a perished valve, and those three are diagnosed and fixed differently.
The frustrating version of this problem is the tyre that keeps going down over weeks with nothing visible in it. That pattern usually points away from the tread and towards the rim or the valve.
The five common causes
| Cause | Typical signs | Repairable? |
|---|---|---|
| Object in the tread | Nail or screw head visible; steady loss over days | Often, if within the repairable area |
| Corroded rim seat | Older alloys; loss with nothing in the tyre; often one wheel repeatedly | Yes — clean and reseat the bead |
| Failed valve | Perished rubber valve, or a leaking TPMS sensor valve | Yes — replace the valve |
| Damaged or buckled wheel | Follows a pothole or kerb strike; may vibrate too | Sometimes — needs assessment |
| Sidewall damage | Cut, scuff or bulge on the side of the tyre | No — replacement |
Rule out the weather first
Air pressure falls as temperature falls — roughly 1 PSI for every 10°C drop. On the first cold morning of autumn, four tyres reading low and a TPMS light coming on is usually physics rather than a puncture.
The distinguishing test A temperature effect shows on all four tyres roughly equally and does not get worse week on week. A leak affects one tyre and keeps returning after you reinflate it.
Finding the leak
- Set all four to the correct cold pressure — from the plate in the door shut, not the tyre sidewall. See correct tyre pressure.
- Write down the readings and the date. Guesswork about "it feels low again" is not diagnosis.
- Re-check after a week, cold. This tells you which tyre and how fast.
- Look over the tread carefully, including between the blocks, for a nail or screw head.
- Check the valve. A little soapy water on the valve will bubble if it is leaking.
- Check around the rim edge where the tyre meets the wheel — bubbles here point at the bead seat.
If you find an object in the tread, leave it in place until the tyre can be looked at. Pulling a nail out turns a slow leak into a flat.
Corroded rims: the one people miss
Alloy wheels corrode where the tyre bead seals against them, particularly on older cars and after winters of road salt. The corrosion breaks the seal, and air escapes slowly around the edge of the wheel with nothing at all wrong with the tyre.
The fix is to break the tyre off the rim, clean the seat back to clean metal, and reseat it. It is a proper repair rather than a bodge, but it does mean the wheel has to come off and the tyre has to come off the wheel — which is why "there is nothing in it" is not the same as "there is nothing wrong".
Valves are a wear item
Rubber valves perish, crack at the base and leak. They are inexpensive and should be replaced whenever a new tyre is fitted — if a fitter is not including a new valve, ask why.
Cars with direct TPMS have a sensor built into the valve. Those have a rubber or metal seal that ages, and a service kit is normally replaced at each tyre change. A leaking sensor valve produces exactly the same symptom as a slow puncture.
Why you should not just keep topping it up
Under-inflation is its own hazard A tyre running low flexes more, builds heat, wears its shoulders out and lengthens braking distances. Repeatedly reinflating a leaking tyre without finding the cause means driving most of the time under-inflated, and risks turning a repairable puncture into a scrapped tyre.
There is also a repair window. A puncture found early is usually repairable; the same puncture after weeks of running soft will often have damaged the inner liner beyond repair. Can a puncture be repaired? sets out where the limits are.
Common questions
- How much pressure loss is normal?
- Around 1 to 2 PSI a month through the rubber itself, plus temperature effects. Several PSI a week is not normal.
- Can a slow puncture be repaired?
- Often, if the damage is within the central portion of the tread and small enough. Never if it is in the sidewall — see sidewall damage and bulges.
- Is it safe to drive on a slow puncture?
- For short distances at correct pressure, generally yes — but get it inspected within days, and check the pressure before every journey until it is fixed. Can you drive with a puncture? covers where the line is.
- My TPMS light keeps coming back after resetting it.
- Then it is telling you something. Never reset the light as a way of making the problem go away — see the TPMS warning light.
Getting it looked at
We can find and repair a slow leak at your home or workplace — including the rim and valve causes, which need the tyre off the wheel. Call 07989 606060 or see mobile tyre repair.
