What is the name of the core of a bicycle

Bike advice

From the range of different fiber composite materials, CFRP (carbon fiber reinforced plastics, colloquially simply called “carbon”) is particularly relevant for bicycle frame construction. The material-related advantages, in particular the ratio of weight to rigidity and strength, of CFRP are significant. Actually, these properties come into play best when flat profiles are used. Since the design of such frames takes getting used to, they have so far not been able to establish themselves with series bikes. High-quality CFRP constructions are made "as if from one piece". So there are no adhesive connections between the individual subsegments, even if they are designed in a "tube shape".
From a technical and physical point of view, CFRP frames offer attractive properties:
• High rigidity and strength with low weight.
• Corrosion resistance and freedom of design in the construction.
• Theoretically, CFRP components could be designed to be almost optimally elastic or stiff.
In practice, however, there are a number of circumstances that stand in the way of this, such as the restriction of design freedom through standardized components (steering head bearings, steerer, etc.). In addition, great efforts (material tests, calculations, manufacturing techniques, etc.) are required to achieve optimal and consistent technical properties. Effort means costs. This means that the CFRP revolution is also subject to price limits.
• In addition to the possibilities of lightweight construction, the freedom in design should be emphasized. That is why CFRP is often the favorite material of designers.
However, CFRP also has a number of disadvantages:
• Because of the high manufacturing costs, there is usually only a limited selection of frame sizes for each model. Under certain circumstances, this means a restriction in the adjustment options of the frame to body size, seating position and individual needs.
• Sensitivity to scratching and abrasion.
• Ecologically questionable if the matrix is ​​made of epoxy resin (not recyclable, harmful to health during processing).
• Safety concerns due to the low elongation at break. If the component is overstrained, the low elongation at break results in a brittle fracture. This means that there is no plastic deformation of the material, but rather an immediate failure / breaking off. The resulting sharp edges lead to a further increase in the risk of injury.
• Little repairability (e.g. if material repairs are required).

Areas of application of CFRP in bicycle frame construction
If processed correctly, CFRP is the high-end material in bicycle construction. In the case of MTB, racing bike, cross and fitness bike frames, the top products are almost entirely made of it. There are already high-performance frames in the upper middle class. Since weight is not as high a priority for other types of bicycles, such as trekking bikes, as it is for sporting purposes, frames made of CFRP are a rather rare occurrence there.

CFRP forks
Carbon forks are almost standard on racing bikes. The situation is similar with cross and fitness bikes. There are full carbon forks as well as those with an aluminum steerer tube. In the case of full carbon versions, the area of ​​the ahead stem clamping can generally be a problem zone, because CFRP components are not suitable for pressure loads, which is why it requires a functional design (e.g. an integrated aluminum sleeve) so that the clamping forces required for the stem assembly are survived unscathed.
A carbon fork is also usually used for niche products such as titanium frames. Aluminum forks can only be found on racing bikes in the lower price ranges.

Materials and processing characteristics
The matrix is the plastic (usually epoxy resin) in which the fibers are embedded. It fixes the fibers and transfers forces to them. Due to the merely "connecting" effect, the aim is to keep the matrix proportions as low as possible in the overall network.
The Fibers are the actual “load carriers” in the composite material. They can only take loads in the direction of the grain, not across it. For the resilience of the finished fiber composite material, both the load-appropriate alignment and the properties of the respective fibers are decisive. Carbon fibers have enormous strength, a low specific weight and minimal elongation at break (= high brittleness). To compensate for the disadvantage of brittleness, some manufacturers add aramid fibers as an admixture.
The individual fibers are combined into threads / fiber bundles, which in turn become woven fabrics. There are mats and "stockings", the threads of which can be interwoven in a wide variety of directions and thus guarantee the requirements for frame-appropriate use. With the "monocoque shape", the advantages of CFRP can be fully exploited. With the pseudo-monocoques (glued connections) the joints are problem areas. Monocoque frames are complex hollow bodies, so they are expensive to manufacture. They are manufactured either in hollow forms or in forms with a core (lightweight rigid foam. Rigid foam cores add weight, but also provide acoustic and mechanical damping. A monocoque also has eyelets, nipples, threads and other details for attaching the Components made of aluminum are used, especially in places where threads are required (e.g. bottom bracket housings).