Is more always better? Not always. With current technology, it would not be a difficult task designing frames or components to be stiffer, and even lighter than the ones available now. But, what happens if too much rigidity in the components compromises the overall working of a bicycle? We explain why everything has a limit when choosing the right amount of stiffness in each component and why stiffness is important if we want to get the most out of our bicycle.
If you spoke to any frame or component manufacturer they would warn you that too much stiffness can be on occasions negative. They would also say that they could produce a component so stiff, that flex in the material would be almost non-existent. They would also tell you that could even make them lighter. Luckily for us, the engineers that design the frames and components that we use, know that when we apply a certain force or pressure on these parts, there should exist a certain amount of “give” so that the energy can be transferred in and adequate way. There is energy that is transmitted, energy that is returned and energy that is lost and they all have an important role to play.
CARBON FIBRE AND ITS CAPABILITIES
Although not all manufacturers use carbon fibre to produce components, it is without doubt the material that can be manipulated the most to determine the rigidity of a component. The quality of the fibres, the number of layers, the angle of layers in relation to each other, the type of resin used to cure it and the different manufacturing techniques are so varied that it allows the manufacturer to find the perfect combination of all the factors that they are looking for when designing a component. A handlebar for example, needs to be stiff enough so when we hold on during a sprint it will not flex too much, but it also needs to absorb small vibrations and impacts and give a comfortable ride when passing uneven or rough terrain. This is something of vital importance in the rear triangle of a frame for example. The end goal is for the stays to transmit the most amount of energy from the pedals to the rear wheel, but at the same time they also need to flex enough to absorb small vibrations and impacts, giving the frame a more comfortable ride.
One thing that is very important in all of this is the definition of rigidity. We could say that rigidity is the resistance to elastic deformation, and that elasticity is the capability of the material to deform under loads or sudden forces and return to its original form. We also need to take into account that when using aluminium to produce a frame, no matter which type, the only way to make it stiffer is to use bigger or thicker tubing. But with carbon fibre, you can dramatically change the stiffness by using different types of fibres, laying them at different angles and the resin that we use or even the way that they are set and cured.
At Rotor we have been using aluminium for many years in our cranksets, by using the TDS system (Trinity Drilling System) we are able to produce extremely light cranks, and to not compromise on stiffness, we use our own ‘Twin Leg’ technology, which allows us to achieve a crankset that has a perfect balance of stiffness between the two cranks. There is no point making a super stiff right hand side crank, if the left hand side is too flexy.
ELASTICITY IS THE KEY TO RIGIDITY
The stiffness of certain components is important. It is fundamental that parts like handlebars, stems, seat posts and cranks are stiff enough to transmit all the energy we input to the rear wheel, and from there to the ground. In every pedal stroke we lose energy, and if all these components were too flexy, then very little energy would transferred to where it is needed, losing valuable watts. This is the reason why SPD pedals were introduced, to efficiently transmit all the power to the cranks, along with the extra rigid soles of road shoes. This same principle is true to the crankset as well, they need to transmit all that power to the bottom bracket and in turn to the chainring, chain, rear sprocket and ultimately to the rear wheel. With other components like the handlebar and stem, a balance is needed between stiffness and elasticity to offer certain comfort, and also to absorb small impact from the terrain. Professional racers for example will look for higher stiffness in detriment to confront and elasticity, they would prefer a set of cranks or a bar and stem that are extremely rigid, and will overlook the lack of comfort as a trade off.
On the other hand, you have cyclists who will look for components with a focus on bump absorption and optimum stiffness. This is the reason behind why high end components are oriented towards efficiency and not comfort, to be able to transmit as much of the energy the rider puts into the bike as possible to the ground.
There are evidently many factors to take into account that can influence the stiffness of a component, It is not just about the materials, like aluminium, carbon or the type of carbon used, but sizes and lengths are fundamental to obtain a stiffness to the degree desired. The rigidity of a set of 165mm cranks will not be the same as that of a set of 180mm cranks, or a 420mm wide bar compared to a 460mm wide one, or a seat post that is too far out of a frame, or a 130mm long stem or a small compact frame compared to a very large one… The key is to find a balance between stiffness, elasticity and weight in function to the needs of each cyclist.