Adding air lightens the load, which can lead to a misunderstanding.

The misunderstanding is, "The more air I put in, the less pedaling resistance there will be."

Here, we will explain what happens if a bicycle's tire pressure is too high.

Optimal Tire Pressure

Bicycle tires have an optimal tire pressure.

In reality, you put air into the tube, but since the tube is inside the tire, you can't normally see it.

Therefore, the tire itself states the appropriate pressure.

What's a bit troublesome is that there are typically four units of measurement.

・bar

・PSI

・kPa (kilopascal)

・kgf/cm2 (kilogram-force per square centimeter)

Since different units are used in different countries, the common units for the country of manufacture or export are often listed.

Incidentally, in Japan, kPa (kilopascal), an SI unit, is standard, but you wouldn't go to a butcher shop and say, "I'd like 20 N (Newtons) of sliced pork."

You'd say, "I'd like 200g (grams) of sliced pork," which I think you'll understand.

These are industrial units, which have been commonly used in Japan for a long time.

And even now, they remain mainstream.

However, in mechanical and architectural fields, it is rare to discuss things in industrial units like kg; discussions are almost always in SI units like N (Newtons).

A common misunderstanding is often asking, "What's the right pressure for a mini velo?" or "What's normal for a road bike?"

Actually, the specified pressure differs depending on the tire product, not the type of bicycle.

I'm not sure if it's the material used, or the tire's diameter or width, but it's certainly true that even with the same diameter, the specified pressures can be different.

Therefore, while examples can be given as shown in the figure above, "what's normal" is a rather difficult question to answer.

Optimal tire pressure also has a range

As far as the author knows, tire pressure is almost always written in two or more units.

And sometimes a range is specified, and sometimes only an upper limit is specified.

If the tire pressure isn't above a certain level, the rim can pinch the tube at small bumps, such as when going from the road to the sidewalk, making punctures more likely.

Since very few people ride with a deflated tire, there are cases where the optimal range is set as ○kgf/㎠ to ○kgf/㎠ within common sense limits, or an upper limit is set as ○kgf/㎠ or less.

Since these are just different approaches, it's safe to assume there's no inherent difference between them.

When a range is specified, the lower limit often appears to be about 70% of the upper limit, so as long as you inflate the tire without exceeding the upper limit, there should be no problem.

Also, air gradually leaks out over a certain period.

We recommend checking it regularly.

While there are no particular rules, please refer to the following based on experience.

Light roadster, city bike... once every 7 days

Mini velo... once every 4 days

Cross bike... once every 6 days

Road bike... once every 5 days

These are reference values, assuming daily riding and commuting/schooling for more than 5 km.

I think it's fine to check it a little every weekend.

Sports bicycle tires are narrow.

For road bikes and cross bikes, the tire diameter is often 700 (equivalent to 27 inches) with widths of 25 or 23.

Simply put, the tires are narrower, resulting in less contact resistance with the ground.

In the past, the prevailing idea was that the less ground contact resistance, the better, so tires became increasingly narrow, and at one point, 23mm was the mainstream.

More recently, the idea has emerged that below a certain point, a lack of grip becomes counterproductive.

Since ground contact resistance and grip are essentially the same thing, there must be a "just right" point somewhere.

Even at 25mm, the width is sufficiently narrow and resistance is low compared to mamachari (city bikes), so I think this is a matter of personal preference.

What happens if tire pressure is too high?

Both have an upper limit specified, so there's no problem as long as you don't exceed it when adding air. However, if you mistakenly think "the more air, the lighter the pedals" and inflate without checking the pressure, there's a risk of a burst (tire explosion) at worst.

This is especially dangerous when tires have deteriorated.

The author made this mistake over 10 years ago, so once you see it, you probably won't make that mistake again.

Degraded tires become more prone to tearing.

In that state, if excessive force continues to be applied from the inside, the tube will bulge out from the inside and tear the tire, as shown in the figure above.

If this happens while riding, the tube will also burst, which is quite dangerous.

It's important to regularly check your tires and tire pressure.

Writer: Koichi Okuno