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triathlon, 09/2013
Reading time 3:00 minutes

The second wave

Cracked carbon tubes and broken frames are failures you hear people taking about again and again. Test engineer Philipp Groten about the pros and cons of the material.

Mr Groten, carbon increasingly eliminates alu as material for frames and components. Justified or not? 

Well, the composite material pushes the boundaries of traditional metal materials in many respects. In the case of frames and forks the weights could be reduced considerably. Today, light weigh forks weigh half and frames about a third of what these components – previously made of steel – used to weigh. In addition, this "diet" was not at the expense of the riding characteristics. Many of today’s carbon frames provide more riding stability and clearly more comfort than frames made of aluminium, steel or titanium. One of the major advantages is the shape flexibility the material offers. Organically shaped and aerodynamically optimized bearing components can only be designed with carbon. State-of-the-art time trial machines are not realisable with any other material. 

Where are the limits of these materials?

Reduced pressure resistance, brittle fracture properties and thermal sensitivity are the disadvantages of the fibre-reinforced plastic. The limits of the material carbon are therefore set by the suitability for use. As long as a bicycle made of carbon can be used, there is no need to worry. However, as soon as it is mounted in a work stand or someone starts any mounting on it or again as soon as it topples over, it is at risk of getting damaged. Another critical point for example are the more and more minimized drop-outs etc.

Is there a higher risk for me as an athlete to use carbon parts instead of alu parts?

If handled properly, mounted carefully and used according to its intended use, the carbon parts of serious manufacturers do not pose a threat.  However, the same also applies to aluminium. Many carbon wheels are yet an exception to this. The braking behaviour with regard to effectiveness and controllability, in particular in rainy weather, is not comparable to that of aluminium. In addition, braking heat as a result of longer downhill rides can heat up the resin and make it soft thus damaging the rim. In the case of carbon rims this is particularly critical for clincher and folding tyres, as in the worst case the inner tube can burst.

Taking account of the material’s sensitive reaction, do I have to fear that my bike collapses under my back, once it has toppled over?

Assuming careful fabrication a crack in the top tube does not mean that the feared "sudden death", i.e. the sudden collapse of the structure, is about to happen. Adjacent fibres bear the load, thus ensuring a residual load bearing capacity. Nevertheless, a damaged top tube or a cracked rear stay should be repaired immediately, which is meanwhile offered by specialist bike shops. Some manufacturers also offer a Crash-Replacement at favourable conditions for such kind of mishaps.

How has carbon processing and the quality of the components in the bicycle industry developed over the years and where is still backlog demand?

We are currently in the second carbon wave. The first one at the end of the eighties with the legendary, aerodynamically shaped "Kestrel 4000", with which many triathlon races were won, was still on a level strongly in need of improvement. About ten years ago the second age started with companies which accorded more importance to sophisticated fabrication methods and in particular to quality control as well as to pre-series tests. In my opinion the major task right now is to refrain from constantly trying to reduce weight. The suitability of some products is doubtful. The lighter the products, the less these products forgive mistakes in the usage. Whoever purchases a light product is obliged to handle it carefully and professionally. Otherwise you may be forced to by a new one.

Philipp Groten

The engineer (master of science) has already dealt in his bachelor theses with the development of a test stand. After having obtained his master degree he joined the team of "Zedler – Institut für Fahrradtechnik und -Sicherheit GmbH" as test engineer entrusted with the construction of testing systems and helps the team with the test orders.

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