Tires, too early to change, too late to change🚗💭

"When should I change the tires?"

Have you ever had trouble being told "it's about time" at a dealer 🍋

Actually changing tires,

There was a structure to lose even if it was too early or too late.

What you want to know in order not to lose,

Three axes and "optimal zone" ✨

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🔖 rainy day, it changes so far in the ditch

Actual measurement test conducted by JAF in 2023.

With summer tires, 100 km / h, wet road surface,

Measured braking distance (distance to stop) due to difference in residual groove.

[New 8mm] 47.6m

[Residual groove 4mm] 50.8m

[Residual groove 1.6mm (legal limit)] 70.5m

The result is + 22.9m, about 1.5 times longer than the new one 💡

This is "The distance that can not be stopped is extended more than one car" level.

On the highway on a rainy day and on the road running with children,

This difference is directly linked to the safety margin.

By the way, the opposite trend on dry roads,

The shallower the groove, the wider the ground contact area and the shorter the braking distance.

I tend to think that "So even a reduced tire is okay,"

It is structured so that the risk rises at once on a rainy day ⚠️

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🔖 tire life is determined by three axes

The life of a tire is not determined by "mileage alone."

It has a structure in which three axes proceed independently 📌

[Axis 1: Mileage (physical wear)]

Estimated wear is about 1 mm per 5,000 km.

From new 8mm to legal limit 1.6mm, usable width is 6.4mm.

In other words, if you look only at the mileage, about 30,000 km is a measure of life.

According to the Sony Insurance 2022 survey,

The average annual mileage of Japanese drivers is 6,727 km.

With this calculation, we will reach the limit in about 4.6 years.

[Axis 2: Years (Chemical aging)]

Tire manufacturers recommend 4-5 years from production.

The time when the phenomenon of rubber hardening becomes easier to proceed.

Even if the mileage is short, the replacement time comes with the number of years.

[Axis 3: Environment (factors that accelerate deterioration)]

UV light, temperature difference, road surface condition.

Outdoor parking · In areas with severe temperature differences,

Degradation tends to proceed at 1.2 to 1.5 times speed.

Even if the mileage is short, if the shaft 2 advances,

Even if the number of years is shallow, exchange if axis 1 advances.

* * The correct answer changes depending on which limit you reach first * * 🌿

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🔖 Study on Tire Change

Here, I would like to introduce two overseas academic studies 📚

Świeczko-urek et al. 2017

Actual measurement study published in Combustion Engines.

The test trailer measures the rolling resistance of the tires on the actual road surface.

In summary, "When rolling resistance changes by 50%,

Energy consumption fluctuates by about 15%.

In other words, the ease of rolling the tire,

Structure that moves fuel consumption greatly ✨

If you keep on wearing old and hardened tires,

It is also easy to lose money in terms of fuel efficiency.

Stabile et al. 2025

Comprehensive review of Engineering Science and Technology.

In a study that comprehensively summarizes the aging mechanism of tires,

As the rubber hardens, the risk of damage increases and traction decreases.

It is said that "handling deterioration" is likely to occur.

⚠️ this is the part I want you to pay attention to.

It's not a story to assume that "people wearing old tires are dangerous,"

"Because there is a structure that changes properties over time,

I want to have a habit of checking sometimes 🌸

Study 1 is "fuel efficiency" and Study 2 is "safety."

From different angles,

It has a structure that shows the risk of continuing to wear tires for a long time.

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🔖 by mileage, 3 patterns of exchange timing

Get closer to your story from here.

I organized the guide by annual mileage 🪞

[Pattern A: Less than 5,000km / year (weekend drivers)]

Cases where aged deterioration precedes wear.

The limit of the number of years will come in 4-5 years.

I tend to think, "It's okay because I don't ride much,"

Even if grooves remain, the life of the rubber comes first.

I want to be conscious of the number of years as much as the car I only ride on weekends.

[Pattern B: 5,000-15,000 km / year (general use)]

A case where wear and aging proceed in a well-balanced manner.

Estimated to approach 3-4mm remaining groove in 3-4 years.

It is natural to look at it at the timing of vehicle inspection and inspection.

A pattern close to the average usage of Japanese people.

[Pattern C: 15,000 km or more per year (commuting / long distance)]

Cases where wear precedes aging.

Approaching 3-4mm remaining groove in 2-3 years.

It is better to replace it early before feeling fuel efficiency deterioration

Structure that often becomes profitable as a result.

In the field view of the mechanic,

"Be careful with grooves less than 4mm, replace with 2-3mm"

It is shared as a guide 🔍

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🔖 psychological trap "I can't change it because it's a waste"

Finally, a little bit about behavioral economics.

In a 2017 study (Journal of Economic Psychology),

The psychology of "thunkcost bias" has been verified.

I feel that this is a waste of investment so far,

A human tendency to become unable to make rational judgments.

When replaced with tires,

"With the tires worn so far, it should be able to be used a little more."

That feeling is likely to be a factor delaying the exchange 💭

Moreover, in the study,

* * People with higher cognitive abilities are more likely to be bound by sunk costs * *

Reversal phenomenon is also shown that.

In other words, the smarter people tend to bend rational judgments due to wasteful behavior.

Take a step back from here,

Just having a perspective to calmly evaluate "safety and fuel efficiency in the next three years,"

Judgment becomes fairly simple ✨

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I look at the tires every day.

Items that I do not know how many mm are left unexpectedly.

There is not one correct answer,

Even if you replace it quickly or use it for a long time,

There is a reason for each judgment 🌿

However, being aware of the three axes (residual groove x years x usage),

Sometimes I look at the tires of my car,

You can see what you want to consult with at the next inspection.

Next time you look at the tires,

I just want you to check three 📌

① How many mm is the residual groove?

How many years ago was the tire?

③ Are you worried about rainy days and highways?

If even one thing bothers you,

It is also a good choice to consult a professional for inspection.

The timing you choose for yourself,

It will be right for you ✨

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