As the name suggests, "carbon spoke wheels" are wheels that use carbon spokes and carbon rims.

Normal spokes are made of steel, stainless steel, or aluminum.

Rarer materials include titanium and nylon resin.

And there are also carbon spokes, which are currently a hot topic. Wheels with both carbon rims and carbon spokes are called carbon spoke wheels.

Especially in the road bike industry, there is a trend that "carbon is the strongest," so one might expect many options, but surprisingly, there are few types when you look for them.

This time, we will provide information on materials, which is a bit niche, as clearly as possible.

The Appeal of Carbon's Lightness

When considering the lightness of an object, saying "light" or "heavy" is quite subjective.

When asked, "Which is heavier, 100g of iron or 100g of feathers?", some people would answer "iron".

As a prerequisite, both are specified as 100g, so their weight is the same.

It seems like it would take quite a lot of feathers to gather 100g.

The difference between iron and feathers is their "specific gravity."

Specific gravity is a numerical value that indicates "how heavy something is when it has the same size and shape."

Let's list the specific gravity of the above materials.

• Specific Gravity of Each Material (g/cm³)

Iron: 7.87

Stainless steel: 7.6-8.1

Aluminum: 2.7

Titanium: 4.51

Nylon: 1.07-1.09

Carbon: 2.25

It's normal to not feel anything just by looking at this.

As a mechanical designer myself, I will explain it in a slightly easier-to-understand way.

Comparing iron and aluminum, you can see that iron's value is approximately 3 times larger.

This means that if you were to make a bicycle frame of exactly the same shape, an aluminum frame could be made at 1/3 the weight of an iron frame.

If an iron frame weighs 7.87kg, an aluminum frame would weigh 2.7kg.

The specific gravity of stainless steel ranges from 7.6 to 8.1, which indicates a slight variation because it is an alloy.

It is made by mixing multiple metals such as iron and chromium.

Since it contains a high proportion of iron, its specific gravity is close to that of iron, but it is lighter because it is made to be rust-resistant.

Looking at "carbon," the main subject of this discussion, its specific gravity is 2.25.

The Toray T700 and T800 used by ICAN have an even lighter specific gravity of 1.8.

In other words, if you were to make a bicycle frame of the same shape from iron and carbon, roughly speaking, the carbon frame could be made at less than 1/4 the weight.

If an iron frame weighs 7.87kg, a carbon frame would weigh 1.8kg.

It's clear how overwhelmingly light it is.

Lightness isn't everything.

Considering the materials above, nylon is the lightest, so one might think it would be best to make everything out of nylon, but nylon is plastic.

It's easy to imagine that a plastic frame would break with just a slight bump, wouldn't it?

That's where "strength" comes in.

Generally, "tensile strength" is the numerical value that indicates how much force a material can withstand when pulled.

Based on this value, the ease of bending and breaking is calculated.

Let's look at the values for each material.

• Tensile Strength of Each Material (MPa)

Iron (SS400): 400

Stainless steel (SUS304): 505

Aluminum alloy: 600

Titanium alloy: 1250

Nylon: 78

Carbon: 1240

The unit "Mpa" is too specialized, so you can ignore it here.

Just looking at the numbers is fine.

Comparing iron and nylon, it's clear that nylon has only about 1/6 the strength.

And looking at carbon, its 1240Mpa shows it's three times stronger than iron.

By the way, the Toray T700 and T800 used by ICAN have a tensile strength of around 5000Mpa.

Pure iron and pure aluminum are rarely used in general products.

Alloys that have been strengthened and made rust-resistant by mixing them with something else are always used.

While pure carbon has a tensile strength of 1240Mpa, through the research and ingenuity of material manufacturers, it has been enhanced to 4500-5500Mpa.

Toray is a Japanese manufacturer, so Japanese technology is being utilized in this area as well.

As these comparisons show, even just looking at the numbers, carbon is an amazing material.

That's why it's gaining attention.

Flexibility is also necessary.

If carbon is so good, it would be an extreme conclusion to say that buildings and cars should all be made of carbon, but in reality, that's not how the world works.

One of the reasons for this is "flexibility."

You could also call it "toughness."

If you consider iron or aluminum spokes, when you bend them firmly by hand, they bend into a V shape.

However, nylon or carbon hardly bend at all, but snap when a certain amount of force is applied.

This characteristic is called "toughness."

There are suitable materials for each application.

No single material scores 100 points in everything while others score 0; instead, based on your usage and preferences, you might decide that "iron is good," "aluminum is good," or "carbon is good."

Carbon is expensive.

One of the barriers to carbon is its price.

Iron is a relatively inexpensive material, but stainless steel and aluminum are costly.

Even more expensive is carbon.

And ease of processing directly affects the product price.

Did you know that all of ICAN's carbon spoke wheels are handmade?

With so much handiwork involved, it's unavoidable that the price will be somewhat high.

However, the quality is that good.

Being able to see the production process like this gives you peace of mind, knowing how the bicycle you ride is made.

Summary

Considering whether carbon spokes are a good idea or not, for road bikes, I think they are "a good idea."

When prioritizing lightness, carbon is less than 1/4 the weight of iron and over 10 times stronger.

Its effectiveness is significant, as seen in its adoption as material for airplane wings.

However, it is vulnerable to strong impacts, so it is not suitable for uses like BMX, which involve landing from high places.

There is no material that is 100% perfect for all cases.

However, for the bumps and unevenness typically found on Japanese paved roads, carbon spoke wheels are perfectly fine for road bikes. They are "a good idea."

Light and strong, I think it's the best material.

The fact that it's all handmade also adds to its charm.

External Writer: Koichi Okuno