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

Bicycle Cables Explained

This is a physical phenomenon that cannot be avoided.

Incidentally, bicycles use cables in two places.

First, for the brakes.

Since there are two (left and right), that's a total of two cables.

Second, for the gears.

Sometimes referred to as a derailleur, which sounds more stylish.

This also uses a cable to shift gears, so one cable is used here.

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

So, it's clear that a bicycle uses either three or four cables.

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■ What is initial cable stretch?

Cables are made by twisting multiple metal wires together, and then twisting those together further.

Simply put, thin wires are bundled to form a single cable.

Therefore, when pulled, the gaps between the wires become tighter.

Once the cable has tightened, it does not return to its original state.

In other words, it settles into a stretched state compared to its original length.

This is "initial stretch."

Since it's a physical phenomenon, initial stretch will occur no matter how expensive the cable you buy.

This probably doesn't apply to bicycles, but generally, there's something called "pretensioning."

Simply put, it's a method where a load is applied beforehand to induce initial stretch, and then the cable is used in that stretched state.

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

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

■ When does initial stretch occur?

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

Strictly speaking, it stretches based on how much it's been pulled, not just the duration.

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

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

For cables that are 12mm in diameter or so, which would never be used on a bicycle, there was a figure of about 2% stretch, but for the thin cables used on bicycles, this information doesn't seem to be publicly available.

However, if we assume 2%, then for a 2-meter cable, 2000mm × 2% = 40mm (4cm), which is quite a lot of stretch.

In reality (based on my感覚), it's about 20mm, so it's likely around 1% stretch.

■ Identifying initial stretch

In the case of brake cables, the free play in the brake lever will increase.

While applying firm pressure will still engage the brakes, the part with free play means the brakes aren't engaging.

That's dangerous, so it's best to adjust it.

For derailleur (gear shifter) cables, shifting gears becomes difficult.

This is likely due to the cable stretching, making it unable to pull enough to properly shift gears.

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■ How to deal with initial stretch (early stage)

Initial stretch is relatively easy to fix in its early stages.

You don't need any tools, 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.

It's certainly not pleasant to ride a bicycle with poorly functioning brakes.

The state of the brake lever due to initial stretch of the brake cable

There is a screw called an "adjuster bolt" near the brake lever; turn this screw.

Turn it in the direction that tightens the cable, following the right-hand rule, and it should improve to some extent.

■ How to deal with initial stretch (mid-to-later stages)

This "mid-to-later stages" might actually be a contradiction.

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

It absolutely needs to be adjusted.

Here's what it looks like after adjustment.

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

Since it's made of multiple bundled wires, it probably won't snap all at once, but the brakes will become unusable. So, if you feel the cable has stretched beyond the initial stretch phase (i.e., after about a month of purchase), you should consider replacing it.

When it will break is somewhat empirical, but suddenly the brakes will become very stiff.

When that happens, it usually breaks within a relatively short time.

Brake cables are consumables, so rather than telling you how to prevent them from breaking, I'll tell you how to deal with them when they stretch 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 brake shoe arm might spring open.

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

In the tightened case, the red circle in the image indicates where it was previously fixed, and it is now fixed further inward.

In other words, it was fixed at a tighter position than before - the cable has been shortened and then fixed.

If you press too much, the brakes will be constantly engaged, so you need to find the right balance.

I think you'll get the hang of it after a few tries, so please give it a go.

Make sure to fasten the screws securely.

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

External Writer: Koichi Okuno