Background: what makes carbon good?

In fact, 35 years ago, the first racing bike with a carbon frame was in the brochures. The brand was Cadex, and the frame was made of carbon tubing, glued into metal studs. Revolutionary at the time, but outdated. Today’s carbon frames are better in every way. But are they also good?

This article was published this year in the Fall issue of RIDE Magazine.

For 1500 euros you can buy a fantastic racing bike with a carbon frame. You can also just spend ten grand on it. Then you have better parts, stronger and lighter, everyone knows the type designations such as Dura-Ace, Red and Record. But what is different about the framework is often unclear. Lighter, stiffer and faster, but how? What is the difference between regular carbon and good carbon?

We consulted one of the biggest manufacturers of carbon bikes and components in the cycling world, Giant. ‘Good carbon’ is usually interpreted as high quality, fast, light and expensive. That’s why we will soon be talking to Jeff Schneider, who can tell us everything about Cadex’s stuff. The wheels, saddles and handlebars of this brand are sold separately, but are also on the top models of Giant.

Jeff Schneider

Jeff likes to explain what Giant and Cadex have in common. “Giant is one of the world’s largest bicycle brands. We develop and produce everything ourselves, internally or with suppliers that we work closely with. We develop as best as possible within the financial possibilities. This is what Giant is known for, value for money and products for everyone. At Cadex, it works the other way around. Cadex products are the best we can make, and the price tag reflects that.”

Jeff is surprisingly open about the connection between the two brands, Giant being the parent brand and Cadex being one of them. Still, Cadex is certainly not intended to be Giant’s ‘parts brand’. Cadex is also increasingly finding its way to connoisseurs who build their custom bikes with the very best parts.

When we ask what good carbon is, Jeff gets really wild. Years ago he raised the bar for carbon technology with Easton’s CNT carbon. Any serious brand had to improve its products back then, and we’re still reaping the benefits. In order to achieve high-quality carbon, four things must come together: design, fibers, resin and production. Easton strengthened the resin, making the final product inherently better, smart and usable everywhere. Cadex goes two steps further and does not only produce the raw fibers itself.

The most advanced frames are assembled by robotic fingers. The required accuracy cannot be maintained by human hands.

These are bought from Toray, where there is competition with Boeing and Airbus: if planes are sold, the prices go up. Cadex products are made from aviation material. T800, T1000 and even T1100 fibers. The latter in particular have such extreme properties that they cannot simply be used. The higher the number, the stiffer the fibers. And rigid fibers yield a little, so the loads in the carbon are higher. These must be carried on to the next fiber layer via an adhesive bond. That glue, a resin, is made in-house and the recipe is a well-kept secret, adapted to the production techniques that parent company Giant has developed over the past decades, even in-house.

But it’s the design process that makes the biggest difference, says Jeff. “No, we don’t have a secret Cadex laboratory where mad geniuses experiment. We already had enough geniuses in our company when we decided to breathe new life into Cadex five years ago, and now they can really show what they can do without limitations. We once made the first mass-produced carbon bicycle frames under this brand, and now they are parts. Performance comes first, and yes, it costs what it costs. The designs are at the edge of what is technically possible, literally Formula 1 level. The technicians make the prototypes in their laboratory and we have them tested by our professionals. Our race teams literally test labs. Not all ideas end up in the store, that’s the consequence of experimenting. But it gives us the opportunity to develop fantastic products.”

This is a generic piece of carbon twill before being impregnated with resin – Photo: Shutterstock

Production is often the most difficult because what works once in a laboratory suddenly has to be repeated very often. The production engineers are therefore just as important as the designers, their task is often almost impossible. Regular carbon parts are designed in such a way that there is a certain margin in production. If a piece of carbon is crooked by a few millimeters, it has no consequences. At Cadex, every millimeter counts, because overlap means unnecessary material and thus weight, and we don’t want that! It is therefore logical that only the very best production personnel are allowed to work on Cadex products.”

Carbon means carbon. In fact, the main component of charcoal, C is CO2 and what makes rubber tires black. Carbon atoms can form many and strong bonds with their counterparts and thus form long, extremely strong fibers. These are the famous carbon fibers from which bicycle parts and airplane wings are made. How exactly it works is worth a separate article, but it comes down to the fibers being glued together in layers and sometimes woven. These packages, cut into a precisely defined shape, are placed in a mold and glued together. This bonding is done with a resin that must be strong and adhere well to the fibers. All spaces between the fibers must be filled, air bubbles are the beginning of a crack. But too much resin is not good either: the denser the fibers are, the stronger and stiffer the whole is. Therefore, the excess resin must be squeezed out before the mold goes into the oven under pressure. When the resin has hardened, the fibers form an almost unbreakable whole.

Even the lightest carbon parts must meet the same safety requirements as any other bicycle part. An old saying in the cycling industry goes: ‘Light, strong, cheap, pick two’. And since with superlight carbon every flaw has an effect on strength, very strict controls must be carried out. Jeff emphasizes that. “The rims on our Cadex wheels are not painted, you can see the carbon when it comes out of the mold. It is to save weight, paint weighs a lot, but on carbon it is not functional. You would see every wrinkle in the carbon, every air bubble. If there were any imperfections, it would be immediately apparent.”

“There is also no paint on the spokes, they are also made of carbon, and we are very proud of that. Because although carbon fibers are ideally suited to absorb tensile forces, it is very difficult to make nipples on them. The easy way is to glue afterwards, but if such a connection comes loose, the damage is incalculable. So we chose the hard way, using a mechanical clamping connection with a wedge in the spokes. The carbon fibers in the core continue all the way from the hub to the rim. And to properly compress the fibers when the resin hardens, the whole thing is forged under a hydraulic press. I can’t tell you exactly how we do it, but it’s a complicated process that no one else does.’

A carbon rim is hard to make, but not special anymore. Reliable carbon spokes are even harder to make.

Lots of outcomes
In the production of carbon parts and frames, Cadex applies strict quality checks afterwards. It is an open secret that in the production of the lightest and most expensive carbon parts there are relatively many ‘errors’; this means that part of the production does not pass the inspection. This is good because it means that the chance of a defect is very small. The disadvantage is the ‘waste’ of the large amount of labor and the expensive and rare raw materials.

Jeff Schneider is also aware of this. “Cadex products are great, but also so expensive that they only end up with riders for whom performance is most important. Our athletes are winning competitions with it and our customers are running faster and further than ever. In addition, Cadex products last a long time, they are light, but also very strong! That doesn’t mean there’s anything wrong with cheaper, heavier carbon. ‘Mid-range’ carbon is heavier because more material is used. And more fibers means that each fiber has to be a little less stiff. This means cheaper raw materials and easier production. The driving characteristics are not affected, the product is just heavier.”

“Only in the lowest price categories are products that we at Giant do not call carbon, but composites, truly simpler materials. Fiberglass for example. Fiberglass is comparable in strength and stiffness to carbon, but much heavier. You can still make a good product out of it, especially combined with nylon it is suitable for shoe soles and pedals because it is impact resistant. But it is not very light, and that has nothing to do with high-quality carbon.”

Fat finger
How good carbon is changes as technology advances. Jeff: “A Cadex frame from 1987 is heavier and much slacker than a modern aluminum frame. It was much lighter than a steel steed, which was the norm at the time. That development will probably continue for a while, because we are far from using the actual strength of the fibers, each subsequent design and each new production technique makes the carbon a little better.”

“What remains is the attention to detail required in each step of the process. An awkward angle on the drawing will cause poor fiber overlap. A greasy finger reduces the adhesion of the resin and a degree more or less in the oven makes the resin too hard or leaves it soft. Good carbon requires attention and perfection every step of the way, from loose fibers on a bobbin to complete bike in the shop. For both the top model and the budget version.”

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