Bicycles made of carbon fibre have a unique appeal. Light, stiff and stable: modern carbon fibre bicycle frames are considered the ultimate in the sporting goods industry. However, unlike a steel or aluminium frame, no visible tubes are joined together in a carbon frame. The black material therefore raises questions. Questions that we put to Christian Gemperlein, graduate engineer in plastics technology and founder of Bike Ahead Composites. The expert gives us the 20 most important answers on the subject of carbon bike frames.
Production of carbon fibre bicycle frames
1st BIKE: How is a carbon frame produced?
CHRISTIAN GEMPERLEIN: Everything starts with the cutting of the prepreg layers to fit the respective pipes perfectly. We then insert them into a negative mould by hand. In Asian production, the layers are often wrapped around a positive core. The number of layers and their overlap varies depending on the load. Pressure and heat are required for the curing process. In the Far East, this is usually done in a hot press, whereas we work with a large pressurised vessel, also known as an autoclave. After being removed from the mould, the material already has the desired strength, but still needs to be reworked. In other words: grinding parting edges, drilling holes, gluing in metal parts, milling bearing seats. Finally, the carbon part is sealed by us and painted by others.
2. what is the base material for a carbon frame?
So-called prepregs serve as the raw material for a carbon composite. These are pre-produced either as fabric or as unidirectional material by impregnating carbon fibres with resin. These are supplied in large sheets on rolls.
Carbon prepregs: high-tech snippets
3. Are there any relevant prepreg producers in Europe?
There are large prepreg manufacturers in Europe. They are primarily important suppliers to the aviation and automotive industries, which of course purchase completely different quantities compared to the bicycle industry. There are a few tonnes of material in the wing of an aircraft. We don't source our prepreg from Asia either - which probably wouldn't be any cheaper. Prepreg production is one of the keys to ensuring that the component works well later on, as the resin acts as an adhesive in carbon parts. If a poor adhesive is used, a bombproof bond can never be achieved. The best carbon fibre is worthless with an inferior resin or a poor impregnation process. That's why we rely on closely monitored prepreg quality from Europe.
4 Where do the raw materials for carbon prepregs come from?
Carbon fibres mostly come from Japanese manufacturers. Toray, Toho Tenax and Mitsubishi are the three biggest players. The fibre spools are purchased from an impregnator or a weaving mill. There they are combined with resin, which usually comes from large chemical companies. The resulting prepreg raw material can then be further processed.
5. are there also frame builders who produce their own prepreg?
Some Asian producers, such as Giant, manufacture their prepregs in-house. To make this worthwhile, certain quantities have to be realised in processing, as this is also a major investment for the large manufacturers. However, no bicycle brand produces the carbon fibres themselves.
Prices and competition
6. what explains the higher price of a carbon frame compared to an aluminium frame?
Even the raw material is more expensive than an aluminium pipe set, for example. However, the majority of the additional costs can be explained by the added value. Manual labour hours are the biggest cost factor in the manufacturing process. This basically applies to production in Europe as well as production in Asia, albeit at different ratios. In our production in Germany, the raw material only accounts for a small percentage of the costs.
7 How do the large price differences for carbon parts come about?
An inexpensive product from Asia will also always be easier to manufacture. In addition to the amount of manual labour, the price can also be influenced by the choice of fibre. Standard carbon parts are made from the cheapest available fibres. So-called high-modulus fibres have a higher stiffness and can be four or five times more expensive to buy than the standard. Between the two extremes, there are of course a large number of other fibres on the market.
8. is carbon always better than aluminium?
You can't say that in general. It always depends on the application. For example, the technical properties of a carbon stem will not be as good as those of a lightweight aluminium stem. A handlebar-stem combination made of carbon, which replaces a clamp connection with a one-piece construction, is again the more sensible option. Carbon offers just as much freedom in design and shows its advantages best when functions are combined.
From light to super light
9. why are some carbon frames significantly lighter than others?
In addition to the fibres used, the final weight depends heavily on the processing expertise of the producer. Anyone who has to work according to the motto "a lot helps a lot" is not utilising the full potential.
10. what compromises would have to be made in order to build extremely lightweight carbon parts?
The sensitivity that carbon is said to have depends heavily on the manufacturing process. If wall thicknesses are reduced further and further, products will break sooner or later, for example due to external influences. We could also make our products much lighter. They would still be just as durable in terms of their area of application. Of course, they are not always used in ideal conditions. Not every biker is a professional and always hits the ideal line. Crashes and botched landings are just as much a part of it as a bike falling over in the car park. With an enduro frame, it simply has to be clear that it will sometimes take a tumble in the woods at the bike park. This must be taken into account in the design. A mountain bike should be so safe that it will still come down after such an incident.
Stiffness and repair
11. which adjusting screws influence the stiffness of a carbon frame?
The choice of fibre already influences the stiffness. To get the maximum out of a racing bike, for example, you can use highly rigid fibres. But I can also adjust certain flexibilities with carbon. If I want to achieve comfort in my frame, I work with the fibre orientation. I then take the fibre slightly out of its load path. Bicycle parts are always in motion. Every seat post, every handlebar is moved millions of times while riding. Carbon can withstand this much better than metal. It used to be said that lightweight aluminium handlebars had to be replaced after one season. Even a well-made carbon handlebar can normally be used for eight, nine or ten years without any serious crashes.
12. can a damaged carbon part be repaired?
This works and is absolutely justified. In fact, almost all carbon parts can be repaired. There are some repair companies that do really good work and can restore the original strength and appearance. Sometimes, however, the question of cost-effectiveness arises.
Where does carbon come from?
13 Is carbon the Holy Grail of frame materials or will we see even better materials in the future?
When it comes purely to performance, carbon is by far the best material. The ratio of weight, stiffness and fatigue strength is extremely good in a well-made carbon frame. No metallic material comes close. There is currently no material in sight that could replace carbon in the next ten years.
14. does each frame manufacturer have its own carbon production or do they all come from the same factory?
There are good, big players in the Far East who produce frames for many bicycle brands. In fact, almost only Giant and Merida have their own production facilities in Asia. Some brands also have different models produced by different manufacturers. There may be strategic reasons for this, as not all manufacturers are equally good at all processes. For example, some companies have specialised in producing lightweight road bike frames, while others are better at full-suspension enduro frames.
15 Why is the production of carbon parts so geographically centred?
This centring has developed historically. In the past, the bicycle manufacturing industry was also based in Europe and the USA. At some point, production moved away for cost reasons. Cheap manual labour enables low prices. Even in Asia, producers keep moving to the next cheapest country without changing the actual manufacturing process. However, there has never been large-scale carbon fibre production for sporting goods in Europe, only in Asia. The relevant expertise has therefore always been located there.
16 What are the advantages of manufacturing carbon frames in Germany?
Production in Germany can be a quality advantage. This is not always the case and of course depends on the expertise of the respective company. For our brand, however, it is important to develop bike parts ourselves and manufacture them at the same location. This means we have a direct influence on quality and can monitor it constantly. This allows us to maximise product performance. For me as an engineer, it's important to have a say in production.
Sustainability and care
17 How much cheaper could the same carbon parts be produced in Taiwan instead of Germany?
It is impossible to say whether the products would actually be the same in the end. If you had parts produced by a service provider, you would probably have to pay half the price at most. However, even if we were to halve the production costs, we must not forget the quality monitoring. Additional costs would be incurred there before delivery.
18 How does the environmental compatibility of carbon compare to aluminium?
In itself, carbon is not as bad as it is often made out to be. Production is very material-efficient. We use over 90 per cent of a square metre of carbon raw material when cutting it to size. In turn, 100 per cent of the cut prepregs are processed into parts. Compared to aluminium, production is also less energy-intensive. For example, unlike aluminium frames, carbon frames do not have to be post-treated in hardening ovens. Carbon also has a very high fatigue strength. A well-made carbon frame can be ridden for 20 years without hesitation. With a lightweight aluminium frame, you will experience severe fatigue over the course of its service life. The strength decreases and the susceptibility to defects increases. The recyclability of carbon still offers potential for the future. There are currently many endeavours to reuse recycled carbon in almost equivalent parts. But there is still a long way to go.
19 What are the challenges in recycling carbon?
In my opinion, there are two major challenges. Firstly, an energy-efficient process to separate the fibres from the resin. The second major hurdle is not to downcycle the fibres obtained by shredding them, but to make performance components again, i.e. to turn a handlebar back into a handlebar. That would be real recycling.
20. do carbon parts need special care?
Not really. The epoxy resin in which the carbon fibres are embedded is in itself very chemically resistant. Even harsh cleaning agents are rather harmful to the metal parts involved or can attack the paintwork. However, the carbon material does not dissolve and is very robust.
Conclusion
Carbon production fascinates me. I find the differences in material and production particularly exciting. The black wonder stuff raises a lot of questions for the average biker, but they can all be answered. If you want a light, stiff and modern bike frame, there's really no getting round carbon. Especially in the high-end sector, it's possible to create some incredible designs. - Jan Timmermann, BIKE editor
Jan Timmermann
Editor
