Have you ever experienced your bike's brakes gradually becoming less effective? Many people seem to think it's just their imagination or a vague malfunction, but this is actually due to "initial cable stretch."

■ What are bicycle cables?

It's a phenomenon that cannot be avoided due to physics.

By the way, there are two places where cables are used on a bicycle.

The first is the brakes.

There's one on each side, so a total of two cables.

And the second is the derailleur.

It can also be called a gear changer.

This also uses one cable to switch gears.

By the way, if there are derailleurs at both the front and rear, one cable is used for each, making a total of two cables.

So, we've learned that a single bicycle uses three or four cables.

■ What is initial cable stretch?

A cable is made by twisting multiple metal wires together, and then twisting those together further.

Simply put, thin strands of wire are bundled together to form a single cable.

Therefore, when pulled, the gaps between the strands become compacted.

A compacted cable does not return to its original state.

In other words, it settles into a state longer than its initial length.

This is "initial stretch."

Since it's a physical phenomenon, initial stretch will occur no matter how high-quality the cable is.

It probably doesn't apply to bicycles, but generally there's a process called "pretensioning."

Simply put, it's a method where initial stretch is induced by applying load beforehand, and then the cable is used in its stretched state.

I haven't heard of it being done with bicycle cables, but maybe enthusiasts do it?

I think the simplest solution is to install them normally and then readjust them after about a month.

■ When does initial stretch occur?

As the name suggests, initial stretch will typically be experienced within about a month of riding a new bicycle.

Strictly speaking, it stretches not based on time, but on how much it has been pulled.

It's surprisingly difficult to determine exactly how much it stretches.

It seems to vary depending on the cable and how it's twisted.

For cables with a diameter of about 12mm, which would never be used on a bicycle, there were figures of about 2%, but for the thin cables used on bicycles, this information doesn't seem to be publicly available.

However, if we assume 2%, for a 2-meter cable, that would be 2000 mm × 2% = 40 mm (4 cm), which is a considerable stretch.

In reality (though this is anecdotal), it seems to be about 20mm, so roughly 1% stretch.

■ Identifying initial stretch

In the case of brake cables, the play in the brake lever increases.

The brakes will engage if you squeeze firmly, but the brake won't engage during the play.

That's still dangerous, so it's better to adjust it.

(1)

For derailleur cables, it becomes harder to change gears.

This is likely because the cable stretch prevents it from being pulled as far as it needs to be.

■ How to deal with initial stretch (early stage)

Initial stretch can be fixed relatively easily in its early stages.

No tools are needed, nor special knowledge or techniques, so please learn about it and give it a try.

After all, riding a bicycle in comfortable condition makes it safe, enjoyable, and pleasant.

A bicycle with poor brake performance is definitely not pleasant to ride.

How the brake lever looks with an initially stretched brake cable

There's a screw called an "adjusting bolt" near the brake lever; turn this screw.

By turning it according to the right-hand rule, in the direction that tightens the cable, it will improve to some extent.

(2)

■ How to deal with initial stretch (mid-to-late stage)

Referring to this as "mid-to-late stage" might actually be a contradiction.

That's because it's no longer "initial stretch" of the cable, but "deterioration."

It absolutely needs to be adjusted.

After adjustment, it will look like this.

(3)

Compared to initial stretch, the cable will gradually stretch, and once it exceeds a certain point, it will break.

Since multiple strands are bundled together, it probably won't snap all at once, but the brake will become unusable. So, if you notice the cable stretching after the initial stretch period (after about a month of purchase), it's probably best to consider replacing it.

While knowing exactly when it will break is somewhat empirical, the brake will suddenly become stiff at some point.

Then it will break in a relatively short time.

Now, since brake cables are consumables, rather than telling you how to prevent them from breaking, I'll tell you how to deal with the situation when the cable stretches and the brakes become less effective.

Loosen the cable fixing bolt.

If you're working alone, just loosening it is enough, but be careful as the bar holding the brake shoes can spring open.

If you can, working while pressing the part indicated by the arrow will make it easier to tighten the cable.

If it's adjusted, the red circle in the image shows where it was previously fixed, and it's now fixed further inward than that.

(5)

In other words, it was stopped at a tighter position than before, meaning the cable was shortened and fixed.

If you press too much, the brake will remain constantly applied, so a balance is needed to avoid overdoing it.

I think you'll be able to do it after a few failed attempts, so please give it a try.

Please make sure to securely fasten the screws.

If you're concerned, your local bike shop should be able to do it for you.

External writer: Koichi Okuno