Bicycle tubes are filled with air, and if a hole forms in the tube, air leaks out, which is called a flat tire.

Separately, there is a phenomenon where air leaks out gradually.

Since many people seem to be troubled by not knowing the cause, I will explain the cause and countermeasures.

Difference from a normal flat tire

In a normal flat tire, there is a hole in the tube, and air is leaking from there.

If you remove the tire, inflate it with air, and then submerge it in a basin of water, air will leak from the hole, so the location of the puncture can usually be found relatively quickly.

However, with a stealth puncture, even if you put the tube in water to find the puncture, there is no air leak.

One reason this happens is when the hole is extremely small, to the point where no bubbles appear just by quickly submerging it in a basin.

In such cases, it may be possible to find the leak by inflating the tube further and submerging it in the basin of water for 10 to 20 seconds at a time, being careful not to miss even the slightest bubble.

The air leakage phenomenon I'm going to tell you about this time is when the air leakage is so subtle that it cannot be found even with this method.

Common causes and countermeasures for air leaks

In the case of city bikes (mamachari), the tube valve is an "English valve," and deterioration of the valve core rubber is the most suspicious cause.

The valve core rubber is an inexpensive and common part, even sold at 100-yen shops, so if it's discolored or cracked, try replacing it with a new one immediately.

Also, the valve may move inside the wheel, causing air to leak from the valve itself.

I don't think this can be repaired, so you should replace the tube.

If you are using a very thin tube, such as a latex tube for racing, air will leak out quite quickly.

About 1 to 3 atmospheres (1 to 3 bar) will leak overnight.

Generally, tires are used at the following pressures, so even if a road bike's tire pressure is adjusted to 7 bar, it will drop to 6 bar overnight, or even 4 bar depending on the type of tire.

• Recommended tire pressure for general tires

Road bike: 90~125psi / 6.2~8.6bar

Cross bike: 65~100psi / 4.5~6.9bar / 450~690kPa

Mountain bike: 30～50psi / 2.1 ~ 3.4bar

Mamachari: 44psi/3bar/300kPa

Have you ever bought a helium balloon when you were a child because it floated?

You probably also have the experience of it deflating overnight and falling to the ground.

If you magnify rubber with a microscope, you will see many holes.

When air is pumped in, these holes expand, and air tends to leak out more easily.

In other words, all tubes are constantly leaking a small amount of air.

Even a brand new bicycle will have flat tires if left unused for six months or a year.

Lightweight tubes, in particular, are thin, so the amount of leakage is significant.

This is inevitable, and the only way to manage it is to check the air pressure daily.

How to ride a road bike to prevent punctures

• Don't ride on the very edge of the road

First, when you're riding on the road, are you riding over the gutters?

Riding over gutter grates is not good because it causes vibrations, and glass shards and debris on the road flow into the drainage system.

In other words, there are many obstacles over gutters.

If you have a habit of riding right on the edge of the road, your bicycle is more likely to get flat tires.

It is less likely to get a flat tire if you ride near the white line on the road or slightly more towards the center of the road than the white line.

*Please check traffic conditions and ride safely.

In that regard, bicycle paths are maintained so that there are no uneven gutters, making them easy and safe to ride on.

There are types where the road is painted blue or has arrows drawn on it.

• Jump over bumps and obstacles to reduce stress

When going from the road to the sidewalk, or if you have to go over an obstacle on the road, don't just ride over it; lift the front wheel as if you're jumping over it.

When riding on the road, there are countless uneven places where the asphalt is raised or has holes.

The impact on the tires is significantly different between simply riding over these obstacles and lifting the front wheel as if to jump over them.

Tires have tubes and air inside, so they act as a cushion to some extent, but the instantaneous deformation upon impact is greater than you might imagine.

Therefore, if you repeatedly ride over obstacles, the rim tape will deteriorate, damaging the tube and causing punctures.

Also, if the tube itself moves inside the tire and the position of the valve becomes misaligned with the hole in the rim, continuous lateral force, like a guillotine, will be applied, causing air to leak.

In this way, punctures can be prevented by how you ride your road bike daily and the areas where you ride.

External writer: Koichi Okuno