sram xo gxp carbon fiber crank

Carbon fiber bikes and components + Amplitex


Carbon fiber bikes and parts are hot, but are they really that good ? Can you repair a frame that is cracked? Or, you may wonder how much is a carbon fiber repair? This revolutionary composite material have lots of misconceptions around it, and might not be the thing you want.

The prime material for making bikes changed two times in my era, first steel to aluminium, then aluminium to carbon fiber. Aluminium is still the most common frame material today, but that can and will change, depending on energy prices, mostly: making carbon fiber is a very energy intensive process, even more than aluminium, which is also a big sucker.

Common means not necessarily the best. I worked with steel and aluminium a lot, I’m always inclined to use steel whenever I build something, because I know the material better, and few more advantages, like easy weldability. I also love carbon fiber, because it’s a material that has so much good characteristics to dismiss.

What I like about composites like carbon fiber, or fiberglass is that you can use the same tools, same know-how and same aptitude amongst them. Interestingly, a material like carbon fiber, which looks like super high-tech, requires the minimum skills and tools compared to other materials except steel -maybe steel too: you don’t need a TIG welder, you don’t need special bending tools that takes huge amount of money or space, or crazy skills.

The most advanced tool you need to build anything out of carbon fiber to vacuum pump, which even doesn’t take much resources to make one DIY. In fact, it’s not even mandatory. You can go all crazy and even build a small scale autoclave oven, so that you can build carbon fiber bikes like any other legit manufacturer.

There is no perfect material to make bikes, each has their pros and cons.

Sometimes, a bike on paper that you like may not fit your needs or the way you use bikes. That particular type of bike material is carbon fiber for me. Carbon fiber is exceptionally strong, but pretty useless on impacts, especially when it takes a hit to an area that is “not expected”.

This is due to how carbon fiber, or composites in general, works, which doesn’t fit me: I don’t like to baby a bike. I sometimes throw it away. I fall. Or drop something onto it. I don’t use a kickstand, so my bikes fell over all the time.

ud pre preg carbon fiber
This is probably not what you’ re expecting, but UD carbon fiber looks like this. The fancy look that is associated to carbon fiber is carbon fiber weave, sometimes called carbon fiber cloth, have almost no use in bikes.

There is a good reason why almost all tourers have steel bikes. Steel is repairable, is shatterproof unlike carbon fiber and can handle almost all impact no matter where it comes from, comes to. Aluminium is also fragile: In its original form, I mean the aluminium frame, is perfectly robust. However, due to thinner, hydroformed tubes, and weaker strength, even a small dent can compromise its strength and can collapse surprisingly.

Steel is also springy, so when engineered and built correctly, steel bikes are comfortable. It’s not rigid as a carbon fiber frame. In perfect conditions, a carbon fiber frame has immense strength, cannot be comparable to any other material. But there are lots of “IFs”. If not taken a hit…If fibers laid out correctly…If autoclave and resin infusion processes are done well…If reinforced right…

It’s surprisingly hard to find a perfectly made carbon fiber frame, where even 5 digit bikes fail miserably.

Why carbon fiber fails

Strength does not come from the material properties only – correct geometry, clever reinforcement, or engineering, in general, is the key to strength, and most of the time, more critical than the material itself.

For example, even if you lay a 20-meter-long, 10cm square tube and hang it on both ends, it will flex to some degree, and cannot take much load. That’s why bike frames (mostly) have a truss structure, which is a very effective way of distributing the load.

Carbon fiber bike frames fail for lots of reasons, looks like the most prevalent factor being the manufacturers don’t seem to have that much experience, compared to more traditional materials like steel or aluminium. That’s not a huge surprise. Even the aluminium bikes from reputable manufacturers from the early 90s were crap – though the cheap, Chinese aluminium frames now are mostly immensely strong unless they are cutting corners and have zero interest in being a respectable brand.

Contrary to popular belief, carbon fiber as a raw material comes from a very limited number of manufacturers, mostly Japanese and recently Chinese. A good resin is a must to make a strong and durable carbon fiber part, as this is a composite material: epoxy resin is weak, and carbon fiber is not stiff as it is thinner than hair, but these two materials make up an incredible strong material.

Too much resin, or epoxy resin, makes the resulting material easy to fracture, to less of it will cause delamination, shattering, or cracks. The key is to remove unnecessary as much as possible, while uniformly “wet” the fibers, so they all bind together.

Timing is critical, too: bike frames are made by laminations, that are wetted by hand, and rolled/stacked together. Resins are generally fast-setting: so, if the worker lets the resin cure to a limit before adding a new layer, the layers do not bond strong enough, which will later manifest itself as delamination, generally. Then, it’s put to a mold, a bladder inside the tubes is inflated, and sent to an autoclave oven.

sram xo gxp carbon fiber crank
Yeah I know; nobody loves GXP, but this SRAM XO carbon fiber crankset looks gorgeous to me.

What is pre-preg ?

The normal build process (for hand production) is to lay resin-wetted carbon cloth, then vacuum infuses the excess resin, and let it cure.

Pre-preg is resin-infused carbon cloth, which resin is not “activated” – if you worked with resin, or even epoxy-based adhesives, you know that the adhesive is activated by another chemical, called “activator”, or “hardener” depending on chemicals. Pre-preg carbon fiber cloth is generally activated by curing ovens, and autoclaves. There are numerous advantages of using pre-preg:

  • No mess. To hand lay carbon fiber, you use a vacuum pump, nylon, a special cloth that is porous to let excess resin and air bubbles escape, and various types of adhesive tapes. It also takes time.
  • Less labor – you don’t need to make the carbon fiber + resin infusion yourself and clean the mess.
  • Surfaces are more refined.
  • It’s cheaper to buy than to make it yourself.
  • Less curing time.
  • Generally, pre-preg clothes have more uniformity, resulting a better strength.

My take on the carbon fiber frame construction method

What I find the problem in this process is, how each tiny part of carbon fiber come together. What I see in all “factory tour” videos is, pre-preg carbon fiber is glued with liberal amounts of epoxy resin, brushed on, and slapped onto each other.

This makes me wonder, are these resins are perfectly compatible with pre-preg resins? Adhesives are immensely complex to understand. They are using copious amounts of epoxy in critical parts of the frame, like bottom bracket junctions, or places like headtube. When put into a mold and cured, that resin does not have any place to go, right?

Bladder to mold interface can be a tight one, but pushing the frame along the mold would probably cause the resin to move to the bottom. Most likely, some of it would run out of mold, but will leave an oversaturated bottom side, after all.

When carbon fiber frame makers talk about carbon fiber, they talk about carbon fiber itself. Not if the way they build frames is legit or not. I know carbon fiber is VERY safe. Race cars use it. Planes use it. Even some high end boats use it. And I’m talking about a few decades. But the plants they build them, or the people laying carbon fiber clothes one by one do not inspire much confidence in me. Let’s face it; the bike industry has no technological or scientific maturity or know-how like aerospace does.

Every time Hambini crushes a “well-known manufacturer” because they have crooked bottom brackets, I feel validated and also concerned. Should I trust a manufacturer who even lacks the skills, or responsibility to make a proper bottom bracket?

t800 carbon fiber frame
T800 carbon is very high modulus – can also crack like glass. There are several Chinese frames that can surpass few thousands of dollars worth big name brands, at a fraction of price.

Carbon fiber is frighteningly easy to make

2 decades ago, a bunch of idiots I knew made a carbon fiber bike frame. I saw the end result and was looking perfectly fine. Why? Thanks to putty, you can even make a bike frame “look” octagonal. I asked a few questions and understood they have no idea what they did.

Want to make a carbon fiber bike frame and weight or strength is not a concern? Fine then! Get a thick and big enough polystyrene board, find a CNC cutter, stick a aluminium pipe of the correct size to the headtube and bottom bracket, and wrap it with a roll of carbon fiber, brushing on epoxy resin liberally.

Add some extra coats where you think it’s stressed. Sand, apply putty, sand. Congratulations, you have a carbon fiber bike to die for.

On the other hand, try to make a bike out of steel. Let alone mitering the tubes, and welding, just try to braze 0.8mm tubing without getting it red. Learning how to make a steel frame takes probably 10x time and effort, compared to laying up carbon fiber, or fiberglass.

In a market, having a low barrier of entry lowers the price, but also populates the market with low-quality products. Carbon fiber is expensive, but not because it’s hard to make, or labor intensive. It’s expensive because carbon fiber and epoxy resin is expensive.

Carbon fiber bikes are tricky for…carbon fiber itself.

As in aluminium or steel, carbon fiber has multiple “types” – the weave of the carbon cloth, thickness for individual strands, or material of it gives the resultant product a different character. Carbon fiber may be stiff, but like almost every material, it can also flex.

Not every carbon fiber is super stiff – yes; carbon fiber is inherently stiff, but high-modulus carbon fiber is not as stiff as low-modulus. If carbon fiber has no flex, they wouldn’t make bows with it.

Take 2 carbon fiber bikes. If one is super stiff and lightweight, while the other is heavier but less stiff, ditch the first bike. It’s not a decently made bike and will crack at some point. Easy as that! Why? Most bike manufacturers use ultra-high-modulus carbon fiber in their frames. High-modulus carbon fiber have also very high tensile strength. In short, it’s a very hard, stiff, and strong material, but it’s also extremely brittle. It will almost shatter like glass when its limits are exceeded.

That’s why some carbon fiber parts or bikes fail catastrophically while others crack with warning signals. I’ve seen some carbon weaves in some frames, which is “abnormal” because the whole industry seems to be using unidirectional fiber. The carbon weave is heavier, and not as strong as unidirectional cloth.

Well; I say cloth, but that’s plain wrong, because it’s nonwoven, unlike carbon weave. Carbon weave can withstand stress in all directions depending on the weave type, or orientation of fibers. However, your frame will not crack upon impact, at least not a huge one, unlike UD fiber. UD fiber is about 20 times as weak upon impact if the impact comes at 90 degrees to fiber orientation.

Carbon fiber bikes fail, because we don’ t care

The carbon fiber bike craze caused also a “lightweight bikes” frenzy, going to extremes.

Can I build a 6 kg bike, with a midrange aluminium bike frame and components? Probably yes, if it would be driven by a 30kg kid, no more than a few hundred meters. I’d drill everything, including even the cassette cogs and the chain. I’d cut seatpost just below the seatpost clamp. Would sand the frame to half its thickness, also the handlebars, well, basically, everything.

This is what is happening today. I wouldn’t ride a 6 kg bike as a 90+ kg rider.

Looking for lower weight is a juicy metric, but I won’t ride a bike that is looking for a small reason to kill me.

Most road bike riders, actually rich amateurs with no or very low experience on bikes or riding, demand the lightest stuff. Let’s be realistic, so a real rider would pay 15.000$ for a bike. Even most pros use aluminium bikes, or much cheaper models if they’re paying for their frames. Those bikes are show ponies to attract people into buying their midrange bikes.

Why carbon fiber bikes or components are not a good thing

Carbon fiber is unethical.

Be it bikes, rims, or shoes, I will never buy a brand-new carbon fiber product. Buying carbon fiber second-hand is extremely risky, and that’s why I have almost no carbon fiber parts, but that’s not the ethical part of it.

You know why almost all western manufacturers outsource production to China? Just because they’re super cheap? No. They actually do not outsource production, but liabilities. China or any other cheap labor in eastern countries do not have worker rights. They don’t have environmental laws or policies. One bike manufacturer which I don’t remember now describes how the Chinese government instructed carbon fiber bike manufacturers to dump their waste into the ocean!

West turning a blind eye to outsourcing because people can buy cheaper bikes. Then talk about how eco-friendly biking is. Biking, in its current form, is not an eco-friendly business. Carbon fiber bikes are piling up in dumpsters. This composite material is almost not recyclable. Recycling opportunities are very limited. And not just that, too.

PTFE in chain lubes, polyester in clothing, excess consumption due to ever-changing “standards” and now, e-bikes…

Carbon fiber is highly carcinogenic. We don’t know how these people work, in what conditions. Nobody cares, too. By buying carbon fiber parts, we are contributing to human rights and labor violations, too.

giant cadex carbon fiber bike
Giant Cadex 2 carbon fiber bike frame. These lugged, carbon frames both is light and looks good, but tubes separating from lugs plagued the idea and the bikes. Koga also made such frames, probably others, too.


Composite bike frames are fashion items

Manufacturers says carbon fiber parts or bikes are very durable too, which I have doubts too. Even if they are, are they really durable? Durability in practice, not “sit there and exist forever”. Now, the rim brakes are gone forever on road bikes, already.

So, what happens to your frame when you cannot find proper rim brakes or what will you do if your rim brake compatible brifters gone bad? You dump the frame, because you’ll not get a replacement after some time. So, they’re not durable, right?

Bikes are not fashion statements, but you want it to look good. Few years later, your composite bike will look probably too silly and irrelevant to bear, like acid wash denim, or faux fur coats, that you cannot stand them. Steel bikes from any era was cool then, now and forever.

look optimum flax carbon
Look, my favorite road bike brand, makes Carbon + Flax mixed frames. This is used on cheaper models, like this Optimum line. But Flax fibers have a great quality, which lowers vibrations. This is not Bcomp’s flax fiber, Amplitex.

Misconceptions about carbon fiber and composites

They are impossible to repair

I have no idea how this idea come up – probably stemmed from the fact that if your motorcycle helmet drops, or you had an accident with it, you have to replace it. That is, in fact, true: but the construction, intended use, even the materials are different.

Carbon fiber is easy to repair. If there is a scale of repairability of ten, I’d rate aluminium bikes at 2, steel 8, and carbon fiber…hmm…8, or even 9 ?

Yes! I’d even rate them higher than steel, which is somewhat tricky to braze, but almost impossible to weld for a weekend welder. Especially, newer, or quality bikes having high-end, butted tubes like Colombus, Reynolds, etc.

Problem with carbon fiber repairs is not the repair itself but assessing the extent of the damage and longevity of the repair. Every damage is repairable, it comes down to how much effort and money you want to spend on it. These days, there are even repair kits sold for relatively simple repairs.

Carbon fiber is eternal – unlimited shelf life

Wish that was true, because it’s heartbreaking to see a Ferrari F40 goes to salvage yard. Nobody exactly knows how long they will survive, but the most optimistic ones are 50 years, if everything is done perfectly and the item stored & cared by the book. Manufacturers are much more pessimistic, they advise to replace components, including frames, every 6 to 10 years.


ferrari f40
Let me tell you a story about Ferrari F40, first carbon fiber body road legal car I know. I first saw it when I was 16-17 years old, and was like a dream. However, I immediately noticed how bad it is put together: horrible body parts alignment, lots of gaps amongst panels, and more strangely, ondulated look – I think that was some exaggerated orange peel problem. There are various rumors about the paintjob. The most popular one being, Ferrari, in order to save weight, painted the car too thin, so much that if you look closely, you can see carbon fiber beneath it. No. I’ve tried. You cannot see carbon fiber. However, the story is somewhat true: carbon fiber cloth created a dimple shaped surface, but Ferrari didn’t want to use putty to fix it, which would add a few extra kg’s. You might ask, why I cannot see that on my bike? Answer is simple. On bikes, they don’t use carbon fiber cloth, at least on majority of them. Even if they use it (some do, for mostly cosmetic purposes) it’s not nowhere thick as the Ferrari used, because cars takes hits.

UV radiation does not effect new resins

UV effects all resins, slowly dissolves them – UV is so strong that it even dissolves our DNA. It’ s the paint, clearcoat and wax that protects your part.

So, we know there are “lightly painted” bikes to reduce weight. That’s a problem: UV dissolves epoxy which can lower the strength by almost 30% – add the lightweight (less carbon, less epoxy) to the mixture, and this is a perfect recipe for disaster.

A natural alternative: Amplitex by Bcomp

Natural fibers like Hem or Flax is not a new idea. They are usually used as a “filler”, or additional layer to glass fibers. But seems like Bcomp, a Swiss company, have a more viable option. This new material is called Amplitex, made from Flax. The exact method of production is unknown – though I might have an idea…

Being a natural product, making the fibers alone is about 100 times(!) less energy intensive, compared to carbon fiber, and 10 times compared to glass fiber. It’s %30 cheaper than carbon fiber, they say, and it’s special resin also includes (but not totally made up of) natural materials.

Porsche, Volvo’s electric car spinoff Polestar, Adidas are the big guns trying and using Amplitex. I don’t have very definitive data about it, but looks like it’s as strong as “entry level” carbon fiber, which is nothing less than great.

Bcomp Amplitex 10
Bcomp’s Amplitex used in a Porsche for testing. It’s natural color is lovely, I liked it much better than carbon fiber.

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