"resumão" de construção bike normal Vs bike reclinada e uso de materiais, pelo Julien Mauroy da Schlitter

Já contei que de vez em quando dou uma entrada no fórum Velorizontal, mesmo sem entender bulhufas de francês. E fico me arriscando no google tradutor.

Pois bem, esses dias um camarada abriu um tópico querendo saber sobre os materiais de construção das bikes, e seus usos/propósitos. Acabou sugerindo a velha discussão alu x carbon.

O Julien Mauroy, designer da Schlitter, deu uma resposta tão completa (e tão bem escrita que chegou a ficar bom no tradutor!) que achei por bem compartilhar. Marquei uma ou outra coisinha em itálico mas tem coisa que só dá pra melhorar se reescrever toda a frase, o que não é meu propósito. Fica então a cargo de cada um.

Imagino que nada seja novidade para os construtores e engenheiros do fórum, mas acho que é uma leitura rara.

Original: http://velorizontal.bbfr.net/t20291-alu-carbone-titane-acier-quel-materiau-pour-quel-usage

Versão traduzida da resposta, em inglês que fica bem melhor que no português (detalhe: VD = "bike normal" (quadro diamante), VH = reclinada, VM = velomóvel)

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The typical response is that it is not so much the nature of the material, [but] the way it is used. Pay attention to the reputations of materials came from the world of VD. They are not always relevant in the field of VH, and certainly modes, marketing and other imitations have their influence. We can not compare what is "ideal" in the context of the industrialization of VD, less constrained by production volume of questions, which is possible in the context of current low volumes VH. Let me explain ... The VD frames (without suspension), with their three triangles, can afford to use all kinds of materials, sections and formatting techniques in the same frame, for example:

* A large section down tube (width limited by the passage of the feet and legs, especially by the limited depth aero rules UCI), resistant to twisting and buckling.
* A horizontal tube a little lighter, especially resistant to buckling, except when part of an interdependent system stays in the manner of a leaf spring, we saw long tubes with double or bifid, or more recently with a pivot system between them and the seat tube (Trek Domane).
* A seat tube sometimes a little more flexible, which may be leaf spring office
* Shrouds (seat stays) which are soaring in a controlled manner as a leaf spring, except when it comes to prioritize aerodynamics (spring function requires to expose a flat surface rather the relative wind)
* Low section bases [chain stays?] (especially when it comes to fit between the large chainring and the tire while maintaining a short wheelbase) but resistant to buckling
* Sheaths (tubos) doing almost the same job as the shrouds [seat stays].

That's why we saw all kinds of mixtures: Solid oblique stays slim tubes, titanium or aluminum frame with carbon seat stays and sometimes bases [chain stays], or more exotic, while titanium frames with carbon seat tube, or the classic part of any kind with carbon fork.

The ideal VD framework may be a mixture of 300 metals, alloys and various composite (like a car) but it is the assembly compromise that take over beyond two or three materials ...

Even inside the single-material frames, all kinds of tricks to arrangement and orientation of the fibers (composite) or play with thicknesses (ex. Shrink / butted) sections (eg hydroforming) and Internal reinforcements are held under the surface and allow the different segments to perform very specific functions.

In design VH, we do not have that luxury!

Recumbent bike frames are almost all more or less curved beams. Some are discontinuous, against-windy places, certainly, but it is rarely complete triangles and joining same nodes so as perfect as those who form a part of VD. All interpretations of these beams are at the base, already less able to resist deformation due to cycling effort than a traditional bicycle frame provided in multiple triangles.

Certainly we saw mixtures of materials (bases or base + carbon shrouds [nos "chain stays" (rear fork) e "seat stays"] with aluminum or titanium frames), but what happening in front of these segments takes place in what can be considered as a single beam.

Up front, we do not have the luxury to assign different properties in various distinct segments in the manner of a VD: the theater of all kinds of constraints going in different directions rather incompatible: lateral buckling and twisting due to the transmission at the bottom bracket and pulley, torsion due to the efforts of the head tube, looking for . some vertical flexibility at the seat.

When using metals, one is faced with a material isotropic (wholesale All "fibers" in the same direction). A beam that is a beam work, brief ["a beam that works as a beam"]. It is possible to vary the sections and thicknesses (purchase of standard round tubes of different sizes and thicknesses, custom extrusion in Challenge and Bacchetta particular), but we are stuck with the same characteristics from one end to the other of the beam.

Anecdote: supply of standard pipe in large sections, thin and relevant alloys is already limited in the aluminum and steel, it is even more so in titanium. Bacchetta was founded on the occasion the discovery of the liquidation of a stock of large section of titanium tubes (60mm?). ATV manufacturer had made ​​a risky investment in the production of such a tube to make oblique tubes and then went bankrupt. These tubes have thus become Ti-Aero. After a little more established market and before emptied titanium tubes reserves, the box has invested to diversify into steel frames, titanium + carbon (Carbon Aero 1), and aluminum and all carbon. Aujourd ' hui [Today], VH titanium production is limited, if I'm not mistaken, at 50mm tubes. This shows how the production of metal VH depends on the supply of tubes available without too much initial investment.

It rest hydroforming, which allows the sections and scalable thicknesses (up to a point). The molds are very expensive and are difficult to amortize on current production volumes VH. Another constraint is the length of such a part is limited to 80cm or 100cm with a little luck (and it's not for lack of personally asked each subcontractor mastering this technique in Taipei furniture). Even stake in butted tubes (butted) with constant section. Too short for a part of VH, except in an assembly, but it multiplies the mussel numbers and therefore investment. Certainly, there are industries capable of swaging or hydroforming longer, but the time to find and refine their application to a bike ... more consequential risks.

Few exceptions: bases and stays ICE mixtures hydroformed parts existing (the mold already exists, are selected in a catalog, the contractor absorbs its mold in a higher cost per part rather than requiring an initial investment) and new molds. Some executives [frames] also Cruzbike, TD [MBB] formula from just within the constraints of length, and the debate on the temerity of this investment would be the subject of another thread ...

Composite materials (we will focus on carbon fiber) are anisotropic (the fiber orientation is determined by the designer). This means that in the surface of what appears to be a simple beam, while a fiber orientation set and thickness is possible. One can imagine several small segments, each playing its distinct role somewhat like a VD setting, all under the surface.

So it becomes a bit more feasible to overcome conflicting constraints mentioned above. That is why in another thread, an owner Schlitter Again [Encore!] quoting the properties that I would translate by little buckling and twisting due to the transmission, but comfort allowed by some vertical movement. Or that more carbon frames owners explain that part "takes but gives" pedaling. By the way I try to avoid the term "rigidity" or "flexibility"[;] too ambiguous!

Finally, the layout of composite materials is - relatively - affordable. It is possible to create molds lost [lost molds] quite easily, reusable molds that do not cost too much, or metal molds capable of producing in series and withstand high pressures, but not too expensive (less than finishing work, some easier to control properties). Hence its relevance to current production volumes VH.

However, there is a huge difference between "form of VH carbon frame object" that can build yourself and what experienced engineers and craftsmen are able to design and implement.

Therefore Malric managed to work wonders with a frame in very curved beam shape, in isotropic materials, is far from being the most likely to respond well to contradictory constraints mentioned above .

So why in another thread I announced, even to promote a competitive product that: The difference between aluminum and carbon, particularly on a framework of VH, far beyond any consideration of weight .

Nino, você por acaso já viu postado em algum lugar o peso do kit quadro da Schlitter, ou alguma comparação com M5 CHR, Zockra ou Carbent em termos de peso?

Mordaz escreveu:

Nino, você por acaso já viu postado em algum lugar o peso do kit quadro da Schlitter, ou alguma comparação com M5 CHR, Zockra ou Carbent em termos de peso?  

Se tivesse visto, com certeza não teria guardado rsrsrs! Minha lerdeza pra guardar informações verdadeiramente relevantes sobre peso é notável. Mas vc viu que num dos tópicos recentes do paul worden, ele diz ter montado a nova CHR dele com "just under 9kg"? Esse just under 9kg pode até ser 8,9kg, mas me parece bem bom pra um quadro de carbono daquele tamanho, e aparentemente dimensionado pra grandes esforços, com grande rigidez! Acho que ainda não vi montagem da schlitter nessa faixa de peso,mas a maioria das que vi são bem "randonneurs", então mal mencionam peso e, se mencionasse, não seria impactante. Carbent com certeza chega; sim, vi uma de 8,4kg.

Sobre o kit quadro da schlitter, realmente não vi, mas no site fala que só o quadro pesa 1,9kg, na versão pra x-seam de 112cm. A título de comparação, apesar de não ser das que vc citou, a Metaphysic de carbono tem mencionado o peso do kit quadro, que é com banco, stays, garfo e guidão, e vai a 4,3kg. Deve pesar um tantinho bom acima de 2kg.

Será que esse tubo da Schlitter tem mesmo todo esse design mencionado no post?  O tubo da Carbent com certeza não tem essa distinção entre flexão vertcal ou lateral, pela própria forma como é fabricado.  Também tenho minhas dúvidas sobre a apicabilidade disso numa stick bike.  Os perfis de aço e de alumínio da Bacchetta, por exemplo, foram projetados para flexionar menos justamente na vertical, ou seja, o contrário do sugerido no post.