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High-end bikes for sale … but what are you really buying?

Much science goes into the creation of the perfect bike frame. Guillaume Horcajuelo/EPA

CYCLING IN AUSTRALIA: What are you paying for when you buy a new bike? Materials … sure. Design … without doubt. Manufacture … yes, of course.

But beyond that, what’s going on? Why can these objects, beautiful as they are, vary so wildly in price, from a couple of hundred dollars to multiple thousands? Are those more expensive, high-end bikes worth it? Well, let’s consider what goes into them.

The international cycling union (UCI) defines rules that determine the fundamental characteristics of the bikes that are used during cycling competitions. The two main rules are the following:

1) Cyclists have to ride bikes that are available on the market.
2) The minimum total weight of the bike as well as the shape and dimensions of the frame elements are constrained.

The geometry, shape and dimensions of road bikes are constrained by UCI rules. From UCI official document.

The “commercially-available” rule was created so that any cyclist can buy the bike that Cadel Evans (BMC Team Machine SLR01 for approximately $13,500) used to win the Tour de France 2011.

The weight rule was defined in January 2000 to ensure the safety of the riders and avoid a technology “arms race”.

It has been defined according to the continuous reduction of the density of the material used to make bike components.

Holding back the years

In the 1980s, a typical high-performance racing bike frame was made of steel tubing. The frame weighed about 1.6kg and the fork weighed about 0.75kg, for a total bicycle weight of about 9.5kg. In the 1990s, aluminium alloy material was introduced, leading to a reduction of the weight to about 1.2kg for the frame, 0.6kg for the forks, and about 8kg for the total bike.

Since the 2000s, spectacular weight reductions have been possible thanks to the introduction of carbon composite material, with bike frame weight reaching as little as 0.8kg and the fork 0.3kg, with a complete bicycle weight of about 6.5kg.

In order to avoid any reduction in bike weights that could compromise the level of safety for cyclists, the UCI currently forbids bicycles lighter than 6.8kgs.

High or low?

Before investing in a $10,000 bike, it’s necessary to understand what the differences are between top-end performance bikes and the more budget-oriented models.

The high-end performance bicycle has mechanical characteristics that provide cyclists with the ultimate level of performance and comfort required by professional cyclists.

A high level of engineering is applied to optimise the bike’s design to satisfy the performance and comfort demands of the best cyclists while respecting the rules defined by the UCI.

“Comfort” is one of the most frequently encountered words during discussions among cyclists, and it’s a crucial aspect for professional cyclists taking part in multistage races such as Le Tour de France.

The mechanical responses of the different components of the bike to the excitation of the road (holes, bumps, etc.) strongly influence the comfort perceived by the cyclists.

From a mechanical point of view, the level of comfort on a bike depends on the energy transmitted by the bike from the road to the cyclist.

To optimise comfort, bicycle frames and forks are made of carbon composite materials that have anisotropic mechanical properties (they do not behave the same way in all directions).

These materials offer an opportunity for bike designers to manipulate a few key areas:

  • the tensile strength (i.e. maximum stress that a material can withstand while being stretched or pulled)
  • stiffness (i.e. Young’s modulus – a measure of the stiffness of an elastic material)
  • the damping properties (i.e. absorption of the vibrations caused by the excitation of the road) of the different frame elements in the various axis or planes, while respecting the dimension and shape rules.

Bike designers optimise the structural characteristics of different bike frame elements by carefully selecting the type of carbon fibers and adjusting their orientation within the bike frame element.

A large number of carbon fibres offering different mechanical properties can be used and combined by the bike designers to optimize the mechanical responses of the bicycle.

Because of the high specific strength (i.e. force-per-unit area at failure) offered by carbon composite materials, it has become possible to build safe bikes lighter than 6.8kgs, so that additional weights are often used in the form of ballast (usually located as low as possible in the frame) to satisfy the minimum weight rule.

Virtual design

The optimisation process is generally completed by combining computer models (e.g. 3D Computer Aided Design model) in conjunction with Finite Element Analysis (FEA).

This approach allows the structural characteristics of different bike frame elements to be created and its mechanical responses under loading condition to be virtually evaluated.

Finite Element Model showing ply-by-ply failure analysis of the head tube area of a composite frame.

Using this approach, bike designers can refine the characteristics of different bike components before the first bike is assembled. The shape of the different bike frame elements can also be fine-tuned in order to optimise the aerodynamic properties of the bike frame and wheels to reduce air resistance.

Using engineering tools such as Computational Fluid Dynamics (CFD) and wind tunnels, this approach has been mainly applied to optimise the air flow-related performance in cycling (see video below).

The cyclists’ body creates most of the aerodynamic resistance.

Power transfer

The most advanced engineering methods are employed by bike designers to optimise the structure of the bike components so that the power transfer between the cyclist and the bike is maximised (performance) while the vibrations generated by the road surface are absorbed (comfort). The shape of bike components is also maximised to reduce the aerodynamic resistances (performance).

Today’s bicycles provide a scientific combination of lightness, strength, stiffness, aerodynamics and damping in order to optimise the transfer of the cyclist’s efforts into bicycle speed while maximising perceived comfort.

All this engineering takes time and costs money, which contributes to the higher cost of top machines. While this technology trickles down the product chain to the lower-end products, compromises are inevitably made, such as using different grade materials and manufacturing methods to maintain the lower costs.

You get what you pay for, in other words, although bikes are getting better for everyone.

This article was co-authored by Raoul Luescher, Director of Luescher Teknik.

Read the rest of Cycling in Australia.

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