Carbon has undergone a development in bicycle construction that hardly any other material has experienced. What was still considered a sensitive high-tech exotic in the early 1990s is now an integral part of the premium and increasingly also the mid-range segment. Road bikes, mountain bikes, gravel bikes, e-bikes and even city bikes now rely on carbon frames as a matter of course - and sometimes also on carbon wheels, handlebars, seat posts and other components. However, despite its widespread use, there are still many misunderstandings surrounding carbon. Reason enough to take a differentiated look at the material - beyond marketing promises and half-knowledge.
Why the carbon frame is not a carbon frame
Even the term "carbon frame" is often misleading. Technically speaking, it is carbon fibre reinforced plastic (CFRP) - a composite material consisting of two central components:
- the carbon fibresthat take up the loads
- and a plastic matrixusually based on epoxy resin, which fixes and protects the fibres and transfers the forces between them
Carbon therefore differs fundamentally from metallic materials. Aluminium, steel or titanium are homogeneous materials with similar properties in all directions. Carbon, on the other hand, is anisotropic: its mechanical properties depend heavily on the fibre orientation, the layup, the resin system and the manufacturing quality.
This means that the properties of a carbon frame are only created during design and production - not in the raw material.
Mechanical properties: Outstanding, but only with the right design
Properly constructed, carbon fibre offers an excellent ratio of weight to stiffness and strength. In the fibre direction, carbon fibres achieve tensile strengths that put almost all other materials in the shade. At the same time, carbon allows stiffness to be built up specifically where it is needed - for example in the bottom bracket or head tube area - and to deliberately allow flex in other areas, for example to increase comfort in the rear triangle.
This ability to control properties in a targeted manner is a decisive advantage, particularly in bicycle construction. A carbon frame does not have to be as stiff as possible everywhere - it can be designed to carry loads efficiently, dampen vibrations and remain durable at the same time.
However, the following also applies: these advantages only exist with proper design and production. Errors in the layer structure, unsuitable fibres or inferior resin systems can result in carbon components not achieving their theoretical properties or, in extreme cases, failing abruptly.
Resin system: The underestimated backbone of the carbon frame
Many articles talk a lot about carbon fibres - the resin system often remains a side issue. Wrongly so. The resin is much more than the "glue" between the fibres:
- It transfers loads between the fibres
- It determines the fracture behaviour (brittle vs. tough)
- It influences ageing resistance and temperature behaviour
- It is decisive for repairability and durability
Incidentally, the term resin system always refers to the overall system consisting of resin, hardener and additives, which is precisely customised to the respective area of application. Modern bicycle frames almost exclusively use epoxy resin systems, as they offer high strength, good fatigue resistance and chemical stability.
Tough modified resins and recyclable or thermoplastic systems are also increasingly becoming the focus of development. These can improve damage behaviour and open up new avenues in recycling in the long term.
Production: High-tech meets manual labour
Despite all the automation, the production of high-quality carbon frames remains extremely labour-intensive. Cutting the prepregs, layering, positioning in the mould and quality control are largely carried out manually. Machines can provide support - for example with CNC cutting or curing - but cannot replace the expertise of experienced specialists.
In bicycle construction in particular, the quality of a carbon frame stands and falls with manufacturing discipline. Small deviations in the resin content, uneven pressure during curing or poorly managed fibre overlaps can later lead to delamination or local weak points.
Durability, damage and repair
A common prejudice is that carbon is fragile and short-lived. Practice shows a more differentiated picture. Well-made carbon frames have a very high fatigue strength and are insensitive to material fatigue - a clear advantage over aluminium.
However, damage diagnosis is problematic: carbon does not deform visibly, damage can be located inside the laminate and a visual inspection alone is often not sufficient. This makes it considerably more difficult to analyse damage after falls.
The good news is that carbon can be repaired. Repairs carried out professionally can almost restore the original strength. The decisive factor here - as with new buildings - is the expertise of the person carrying out the work.
Carbon compared to other materials
Whether a bike frame should be made of carbon, aluminium, steel or titanium is often a matter of taste. But technically speaking, there are clear pros and cons to the different materials. This is because the material determines the weight, riding behaviour, durability and, last but not least, the possible uses of a bike. Titanium plays a special role as a durable precious material. Aluminium was long regarded as the ideal compromise between weight and cost. And steel still stands for robustness, comfort and timelessness. Carbon, on the other hand, has redefined the rules of the game in the high-performance sector, especially as it allows greater design freedom. In order to categorise carbon realistically, it is therefore worth comparing it directly with its alternatives - with a view to objective material properties as well as practical consequences in everyday and sporting use.
Compared to aluminium, carbon offers:
- Lower weight with the same or higher rigidity
- Better fatigue strength
- More constructive freedom
- Aluminium, on the other hand, scores points for its robustness in the event of misuse and easy recyclability
Compared to steel:
- Significantly lighter
- Better mouldability in complex geometries
- Steel remains unbeatable in terms of ease of repair and long-term robustness
Opposite Titan:
- more favourable in relation to performance
- More constructive freedom
- more versatile
- Titanium impresses with its corrosion resistance and durability
Sustainability: better than its reputation
Carbon is often seen as ecologically problematic. In fact, the assessment is complex. On the positive side: The degree of material utilisation is high, i.e. in production, especially when cutting carbon layers, attempts are made to keep waste to a minimum. As carbon is extremely energy-intensive and expensive to produce, high material utilisation is the most important lever for the ecological balance. This is not the case with aluminium and steel, where subtractive work is carried out - parts are often milled from solid blocks or tubes are shortened considerably. Another pro for carbon: the service life
The weak point, however, remains recycling. The separation of fibre and resin is complex and genuine material recycling is still under development. Nevertheless, research is progressing rapidly - particularly in the field of recycled fibres and new matrix systems.
Conclusion: The main thing is well done
Carbon is neither a miracle material nor a bad decision in bicycle construction. It is a highly complex composite material that offers enormous advantages if the design, resin systems and production are perfectly harmonised - and becomes problematic if savings are made in these areas.
When used correctly, carbon fibre enables bicycle frames to be lighter, stiffer, more durable and more comfortable than with other materials. The future of lightweight bicycle construction should therefore not lie in ever more extreme weight records, but in well thought-out and sustainably produced carbon constructions.
Josh Welz
Editor-in-Chief
