Flat bicycle tyre: Why? What should you do?

It is normal for a tyre to slowly deflate all on its own. The air trapped inside your bike tyre is made up of nitrogen and oxygen molecules. These very small molecules can escape through the inner tube and the tyre. This permeability causes the tyre to deflate. Even with a high-quality inner tube and tyre, this loss of pressure is quite normal, but it can take a long time, weeks, or even months.

On the other hand, if the air escapes in a matter of days when the tyre is not punctured the tyre may be damaged, the quality of the inner tube may be poor or the valve may be faulty.

Finally, in hot weather, air expands and occupies more space inside the tyre. This phenomenon can speed up the loss of air. But this loss of air is marginal and is difficult to detect in the short term.

To repair a tyre that deflates slowly, it is necessary to:
👉 Detect where the air escapes from.
To do this, check the sides and the tread of the tyre for wear.
💡 If you find any cracks or abnormal deformation on the sides of the tyre, a flat surface instead of tread, then your tyre is showing signs of serious fatigue. In this case, the tyre is no longer airtight, which explains why it deflates quickly. It must be replaced.
We explain how to replace the tyre of your bike here.

👉 Also, take a look at the inner tube, which may have become porous, or very porous, if it is old. Over time, the quality of the rubber deteriorates and can allow the air to escape in just a few days. Observe the quality of the rubber by stretching the inner tube.
💡 If the inner tube is too elastic and insufficiently dense, then it needs to be replaced.

👉 Check the condition of the valve too. Take out the inner tube, inflate it and immerse in a bucket of water to check whether the air escapes in the shape of bubbles.
💡The inner tube must be replaced if any air escapes.

You can detect a slow puncture according to theme the tyre takes to deflate. If your tyre is flat after a few hours or a few days, then there is almost certainly a hole or a foreign body in the inner tube.

Usually a slow puncture causes the tyre to deflate faster than or natural air loss.

Remember that there may also be a serious defect of the valve or the inner tube. This can result in a loss of air that is sufficiently significant or rapid for you to think that the inner tube is punctured. To be sure, immerse the inner tube and the valve in a bucket of water. If any bubbles rise to the surface, then there is a puncture.

Yes, it is dangerous to ride with a deflated tyre, because the tyre does not provide the same grip, the brakes are less efficient, so the braking distance is longer. In general, road-holding is far less precise with a deflated tyre, the bike wanders, without any real grip on the ground, and with very low pressure, the tyre can even come off the wheel rim and cause you to fall.

Incorrectly inflated tyres are subject to more frequent deformation and punctures.

👉 I expend more energy than usual: when the tyre is not sufficiently inflated, the contact surface with the ground is larger, friction is increased and efficiency is reduced. In other words, you have to expend more energy to ride at the same speed than with correctly inflated tyres.

👉 The lifespan of the tyre is shortened: If your tyre is under- or over-inflated, its structure is subjected to abnormal aggression and forces that reduce its durability and performance.