When considering carbon spoke wheels, "ride comfort" is an inseparable factor.

Looking at online reviews, some people say they are "hard," while others say they are "soft."

Are carbon spoke wheels hard or soft?

Actually, as a big fan of mini velos, I know why this is.

I will explain the misunderstandings about carbon spoke wheels.

One reason for the differing opinions is "whose impression it is."

I usually ride a 20-inch mini velo, but I also ride a 700c x 25 cross bike.

For example, when passing over a manhole cover, I feel a bump whether I'm on a mini velo or a cross bike.

At this point, since the bump is significant, the sensation might vary among individuals, but I think everyone would notice it.

This makes comparison impossible.

I don't feel any bump at all on a mini velo when crossing the difference in level between a road gutter and the asphalt.

On a cross bike, I clearly feel the bump.

At this point, I feel that "the cross bike (700c x 25) has a harder ride."

Compared to this, mini velo tires are quite soft.

Therefore, it's undeniable that someone who usually rides a regular bicycle would feel a carbon spoke wheel bicycle is "hard."

On the other hand, people who regularly ride road bikes are used to narrow tires, so they wouldn't feel a carbon spoke wheel bicycle is "hard."

Rather, it's normal to feel softer compared to steel spokes.

Also, individual perceptions and preconceptions play a role, so those will also have an impact.

■ Mechanical characteristics of carbon

If I were to discuss this purely objectively, without any personal feelings, as a mechanical designer, I covered carbon in another article.

The secret of carbon spoke wheel materials and strength

Comparing specific gravity, steel is 7.87 and carbon is 2.25.

If you made a wheel of exactly the same shape, if it were made of steel, it would weigh 7.87 kg, and if made of carbon, it would weigh 2.25 kg.

This is a material characteristic, so everyone will get 100% the same result.

Next, considering "strength," there is data on "tensile strength," which indicates how much force is needed to tear a material when pulled.

Steel has a tensile strength of 400 MPa, while carbon has 1240 MPa.

Looking at the numbers, carbon is about 3 times stronger.

This tensile strength is also used to calculate how much a material can bend before it breaks, so you can think of it as 1/3 the weight and 3 times the strength.

The Secret to the Lightness of Carbon Spoke Wheels

From here on, the factors change depending on the person, but as mentioned above, it is unlikely that wheels of exactly the same shape would be made from steel and carbon.

If I were to design it, knowing that it is 3 times stronger, I would aim for further weight reduction by making it thinner.

Even if it's simply 1/3 the size, it still has the same strength as steel, so anything more would be considered over-specced.

Even though it's stronger than steel, it will definitely become more flexible if it's made thinner.

Measuring the steel spokes I have on hand, in Japan and Taiwan, they were 13 gauge (2.34mm) and 14 gauge (2mm); for overseas products, they were 1.8mm and 2.0mm. (This is just my own measurement of spokes with calipers, so I'm not sure if it's official.)

Carbon spokes, in the case of aero spokes, are flat, with the narrowest part being 0.9mm and the widest part 2.2mm (Sapim CX-Ray).

It's hard to tell which one is thicker from this, isn't it?

So, let's compare by cross-sectional area.

The cross-sectional area of a spoke with a diameter of 2mm is radius × radius × π, so 1mm × 1mm × 3.14 = 3.14 mm².

On the other hand, the aero spoke measures 0.9mm x 2.2mm, and even if we calculate it as a rectangle ignoring the rounded corners, it's only 1.98 mm².

In reality, since there are no sharp corners, it should be even narrower.

In the example above, the steel:carbon ratio is 3.14:1.98, meaning approximately 30% of the material has been reduced.

In the case of carbon, it is still over-specced, so the gauge can be further reduced.

Even if it's reduced by 66%, it still has the same strength as a steel spoke.

Thus, comparing steel and carbon, not only can the specific gravity be reduced, but also the volume, making it lighter in two ways.

Since they can be made thinner and thus more flexible, it's a natural conclusion that many carbon wheels would offer a softer ride.

However, personal preferences also play a role, so there might be wheels that deliberately feel stiffer without significantly reducing volume. When choosing, paying attention to spoke thickness and count can be helpful.

Summary

Comparing the material properties of steel and carbon, carbon is 1/3 the weight of steel and 3 times stronger.

Because carbon is 3 times stronger in bending and tension than steel, spokes can be made thinner or fewer in number than if made of steel.

While this allows for weight reduction, they can also be made thinner to allow for more flex, so the ride comfort often feels softer compared to steel wheels.

Some are deliberately made stiffer, so comparing spoke thickness and number can be helpful.

External writer: Koichi Okuno