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What is a slow puncture?
A slow puncture is a small, steady air leak: the tyre doesn't go down all at once, but loses pressure over hours or days. You often notice because you keep having to pump up the same tyre or because the pressure warning light comes on.
The most common causes are a small foreign object in the tread, a leaking valve or an imperfect seal between the tyre and the rim. If the tyre is already very low, read the page on a deflated tyre.
How do you do the soapy water test?
The soapy water test is done by spraying a soapy solution on the inflated tyre and watching where bubbles form.
- Bring the tyre to the correct pressure: with little air the leak is harder to see.
- Mix water with a little washing-up liquid in a spray bottle, or in a bowl with a sponge.
- Wet one section of tread at a time and watch for a few seconds.
- Move the car forward slightly (or turn the lifted wheel) to check the whole circumference.
- Wet the valve, with the cap off, and the edge where the tyre meets the rim, on both sides if possible.
- Where growing bubbles form, you've found the leak: mark the spot with chalk.
Where does the leak most often hide?
The leak most often hides in the tread, the valve or along the edge of the rim.
| Location | Clue | More information |
|---|---|---|
| Tread | Nail, screw or small stone embedded; bubbles in one precise spot | Nail in the tyre |
| Valve | Bubbles at the tip or base of the valve | Leaking valve |
| Rim edge | Bubbles along the bead, often with a corroded or damaged rim | The tyre needs to be removed |
| Sidewall | Bubbles from small cuts or cracks | Generally not repairable |
What should you do if you can't find the hole?
If you can't find the hole, the leak may be very small, on the inner side of the wheel or between the rim and the tyre, where it can only be seen with the tyre removed. Don't keep trying on your own.
Check the pressure every day to see how quickly it drops and have the tyre checked by a tyre specialist: with the tyre removed or submerged in a tank, the leak is easier to find.
Can you keep driving with a slow puncture?
With a slow puncture you can only drive if you keep the tyre at the correct pressure, and only for as long as it takes to get it checked. Driving on an under-inflated tyre overheats it and can damage it beyond repair.
If the tyre goes down within a few hours or is already very low, don't carry on: read can you drive on a punctured tyre?
Slow puncture in Milan?
If you're in Milan or the surrounding province and the tyre keeps going down, SOS Tyre comes out 24/7, in 30 minutes on average, even outside your home or in your garage, as a mobile tyre fitter. Call +39 377 326 0999.
Frequently asked questions
Can the soapy water test damage the tyre?
No, a solution of water and ordinary washing-up liquid won't damage the tyre or the rim. Avoid solvents, harsh degreasers or petroleum-based products. After the test you can rinse with clean water and dry the valve before putting the cap back on.
How much pressure can a tyre normally lose?
All tyres lose a little pressure over time, even without holes, which is why it should be checked regularly. But if one tyre drops noticeably more than the others between checks, a slow puncture or a leak from the valve or rim is likely.
Can cold weather look like a slow puncture?
Yes. When the temperature falls, the pressure drops in all the tyres together. The difference is that with a slow puncture the drop affects just one tyre and happens again even after you've brought it back to the correct pressure.
Can I remove the nail I found with the test?
Better not. The nail often partly plugs the hole: pulling it out can suddenly make the leak worse. Mark the spot, check the pressure and have the repair assessed. The technician will remove the foreign object when carrying out the repair.