Wire Types and Differences for Road Bikes, MTB, and Hybrid Bikes

Basics of Bicycle Cables

When we talk about “cables” in general, it typically refers to steel strands twisted into a rope-like shape. In the context of bicycles, these are known as inner cables (or inners).

On the other hand, the outer casing—a tube usually made of plastic that protects the inner cable—is called the outer cable (or outer).

Each has a different role, so when replacing cables, make sure you know which one needs replacement so you can get the correct part.

Also, in high-end modern sports bikes, hydraulic brakes are used instead of cable-actuated brakes. These use hydraulic hoses instead of wires. Likewise, for electronic shifting systems like Shimano Di2, traditional cables are unnecessary; instead, special electronic wires (for power and communication) are used.

Basic Types of Inner Cables

There are two main types of inner cables used on bicycles:

1. Brake cable
2. Shift cable

Brake cables are used to pull the brake caliper via the brake lever, while shift cables move the derailleur via the shift lever.

Not only are their purposes different, but the diameter of each cable also differs.

For example, Shimano’s inner cables are:

• Brake cable: 1.6 mm diameter
• Shift cable: 1.2 mm diameter

This applies to both road bikes and mountain/city bikes.

Because the thickness differs, each requires a dedicated outer cable that matches the specific inner cable type.

Main Difference Between Road and MTB/Cross Inner Cables: the Cable Head (“Taiko”)

Brake Inner Cables Are Not Interchangeable Between Road and MTB

If both road bikes and MTB/city bikes use the same cable thickness, what’s the difference? The key is the “taiko”, the shape of the cable head that connects to the brake lever.

The shape of the cable head differs between road and MTB/city bikes.

• Road bike brake cables use a half-spherical head.
• MTB and city bike cables use a cylindrical head.

This difference exists because the cable is anchored differently inside the brake levers of each type. If the head shape doesn’t match, the cable won’t fit or function properly in the lever.

Difference Between Brake and Shift Inner Cables

Additionally, the shape of the “bottle” (or end fitting) for brake and shift inner cables differs. Due to this difference in shape, they cannot be used interchangeably.

Shift Inner Cables Are Common Between Road and MTB

On the other hand, shift cables share the same “bottle” shape for both road STI levers and MTB shift levers, making them a universal standard.

Thus, replacement shift cables are usually sold without specifying “road” or “MTB,” but this is not an issue as they are compatible.

Shimano offers road-specific shift cable sets, but the main difference lies in the materials of the inner wire and outer cable, making them usable on MTB bikes as well.

How to Decide Which Cable to Choose

If you’re unsure whether your bike uses “road” or “MTB/crossbike” cables, you can check whether your bike has STI levers to make the decision.

If your bike has STI levers, then you should use “road” cables. If the bike uses standard city cycle brakes with a shift lever, you should use “MTB/crossbike” cables.

Differences and Identification of Outer Cables

Outer cables, which protect the inner cables, differ only in thickness between “brake” and “shift” cables; there is no specific distinction between “road” or “MTB.” This is because outer cables do not involve the bottle.

However, outer cables for brakes and shifts are often colored the same, and the thickness difference is only about 1mm, so visually distinguishing them can be challenging.

If you’re replacing cables or working on a build, it’s easy to make a mistake if you remove all the outer cables, as it’s not immediately obvious which one is for brakes and which one is for shifting.

Typically, you can tell by comparing thickness: “thicker” is for brakes and “thinner” is for shifting. But if you’re using Shimano’s genuine outer cables, you can identify them by the logos:

• Brake outer: “SHIMANO SLR” logo
• Shift outer: “SHIMANO SIS” logo

“SLR” is Shimano’s braking standard, and the latest levers and brakes adopt the “NEW SLR” standard.

Meanwhile, “SIS” refers to Shimano’s shift standard, which stands for “SHIMANO INDEX SYSTEM.” All current Shimano shift components adhere to the “SIS” standard.

Knowing these standards guarantees that you’ll know exactly which is for braking and which is for shifting. The subtle silver logo on the outer cables adds a stylish touch, which is typical of Shimano products—they are worth the price.

When to Replace the Cables

Inner Cables Should Be Replaced When Discoloration Appears

Inner cables are shiny silver when new, but if the bike is stored outside or kept indoors for a long time, the exposed parts of the inner cables begin to darken and turn black. This is a sign that the wire is deteriorating.

If only the exposed part is deteriorating, it’s often fine to continue using the cable without replacing it. However, if rust has reached the inner cable inside the outer cable, it can affect braking and shifting, which is a clear indication that it’s time to replace the cable.

Outer Cables Can Be Used as Long as They’re Not Too Heavy

On the other hand, outer cables are built quite sturdily and generally do not degrade. Over time, like 5 or 10 years, they may show signs of aging, but internally they might still be fine. It’s best to judge the condition of the outer cable by the “pulling resistance.”

If you feel that shifting or braking has become heavier than when you first bought the bike, it’s a good idea to consider replacing the outer cable. At this time, replacing the inner cable as well can restore smooth operation, making it feel like new.

Cables Are Actually Important Parts for Comfort

Cables may not be the most talked-about part when it comes to upgrading road bikes, MTB, or cross bikes, but they are actually crucial for the bike’s operation.

There are two types of braking systems on bicycles: “mechanical” and “hydraulic.” The industry is gradually shifting toward hydraulic systems, but many bicycles still use “mechanical” systems.

In mechanical systems, the resistance of the wire directly affects the force needed to pull the brake. High-quality inner and outer cables are designed and manufactured to reduce resistance, making braking and shifting smoother.

While cables may seem trivial, since brakes are frequently used on a bicycle, heavy brake pull can lead to fatigue in your hands during long rides.

People often think that the weight of the brake pull is determined by the brake itself and the lever, but the quality of the cables and their routing also play a significant role.

We have looked at the different types of cables for road bikes, MTB, and cross bikes and the differences between them.

Even something as small as changing the cables can greatly improve your riding comfort, so consider customizing your bike with care.