A slow puncture is the tyre that keeps needing air. It holds pressure for a while, then goes soft again, usually while the other three stay put. Finding it is straightforward; the cause decides whether it is a quick fix or a new tyre.
What causes a slow puncture
Air escapes in only a few places, and each leaves a clue:
- An object in the tread: a nail, screw or shard, sometimes barely visible, letting air past slowly
- A leaking valve, perished with age or never sealed properly
- A corroded rim seal, where the tyre bead meets an alloy that has started to oxidise, common on older wheels
- A failed previous repair that has begun to weep
- Seasonal change, which is not a puncture at all but explains a tyre that only softens in the cold
The soapy-water test
The reliable home method needs only washing-up liquid and water:
- Set the tyre to its correct pressure first, per correct tyre pressure
- Brush or spray a soapy solution over the tread, sidewall, valve and the rim edge
- Watch for bubbles growing where air escapes
- Mark the spot, or note if it is at the valve or rim rather than the tread
A nail in the tread is usually repairable. A leak at the valve or rim seal, or anywhere on the sidewall, means the tyre has to come off the wheel for a proper look.
When it stops being a home job
If the bubbles point to the tread and the object is small and central, it sits inside the repairable area of a tyre and a garage can fix it. If the leak is at the rim, the valve, the shoulder or the sidewall, or if the tyre has been run soft for a while, it needs professional assessment to settle the repair-or-replace decision. A tyre that keeps deflating with no obvious cause is also worth reading about under a tyre that keeps losing pressure.
From the workshop: people assume a slow puncture is always a nail, and often it is. But a good third of them are the alloy quietly corroding where the tyre seals to the rim. You can chase that with soapy water all day and find nothing in the tread. That one's a tyre-off, clean-up and reseal job, not a plug.
Sources and accuracy. This reflects standard diagnosis at the time of writing. A persistent leak should be assessed by a tyre professional. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
How do I find a slow puncture?+
Inflate the tyre to its correct pressure, then brush soapy water over the tread, sidewall, valve and the rim edge. Where air is escaping, the solution bubbles up. A nail or screw is often visible in the tread; a leak at the valve or rim needs a garage to break the tyre down and reseal it.
Is it normal to lose a little pressure over time?+
A small, gradual loss of a few PSI over a month or two is normal, and tyres also read lower in cold weather. A slow puncture is faster and persistent: the same tyre going soft again days after being reset, while the others hold.
Can I keep driving with a slow puncture?+
Only with care, and not for long. Topping the tyre up and getting it inspected within a day or two is reasonable; ignoring it is not, because a soft tyre overheats, wears its edges and can fail. Keep an eye on it and check the pressure before every drive until it is fixed.
Why does my tyre lose pressure only in winter?+
Cold air contracts, so pressures genuinely read lower as temperatures drop, often by a PSI or two for every 5C. If a tyre only ever goes soft in the cold and holds steady otherwise, that is physics rather than a puncture, though a borderline leak can show up first in winter.