The use of 3D physical models to understand the interaction of elements involving the bicycle has been proved to be of great use during the design process of a bicycle, a trail or the training of a rider, as well as in choosing the place and the equipment that best fits the necessities and desires of one rider. Despite some work has been presented in the past, lots of empty blanks are to be filled
The origin of this present initiative was to understand and clear out all the marketing claims made by bicycle suspension manufacturers. In a situation that can be many times compared to a rough sea of acronyms and "new" suspension systems always claiming to be superior to all previous ones, and optimal this and that, it was decided that it was about time for some serious approach to understanding the functioning of a full suspension bicycle in its particular working regimens. Initially, suspension functioning has been described on the vertical plane, in order to understand what actually changes from one suspension scheme to another, and to our pride and desperation, not much really changes, at least when it is analyzed purely as a absorbing device, and that can be seen when the leverage ratio of different systems are plotted to be compared. And in addition to that, spring-damper units have also reached a point where they can be finely tuned to particular needs and appications, to an extent that no matter what your frame kinematics is doing, final wheel behaviour can still be tuned to your preference on what concerns the job of the damper itself. That is very good, after all everybody likes choice, but the analysis cannot be restricted to that. Apart from absorbing terrain irregularities, a suspension system must still be stiff and its interaction with other systems on the vehicle cannot generate problems that were not present before the introduction of suspension to bicycles. Here in short words, braking and propulsion. So, in clear words, no suspension system can totally eliminate the influence of either braking or pedaling optimally. Yes, you can neutralize pedal-suspension interaction effects to a certain gear ratio, to one specific pedaling profile, or one particular braking configuration, in a way that most claims for optimal functioning we find in mountain bike marketing have no technical background. Brake and suspension together, to any kinematic scheme, will result in an additional positive or negative torque acting along the movement of the rear wheel, and not only, once front wheel, despite the simplicity of sliding forks, will also be affected by braking, resulting in different reduced stiffness. A model describing and quantifying this interaction is presented and a few particular cases are presented.
On what concerns pedaling, more factors are present, such as an individual´s pedaling profile that can be so particular as one´s fingerprints. Or still the gear ratio being used. So, in order to keep things clear, on what concerns the frame itself, influence on pedaling performance due to suspension travel is evaluated as variation on the distance between the bottom-bracket and the rear axle along suspension travel.
We have at this point, enough criteria to compare different designs to a level that can satisfactorily allow us to evaluate a bicycle in some of the many situations found in real-life riding.
On what concerns the riding, the first question to be cleared out, was that of how much suspension work is made by the rider, and how much is performed by the suspension system itself. Being the human body an endless source of inspiration and surprise, a complex rider model is defined, and the parameters that reflect its functioning as suspension are evaluated. Said that, it is possible at this point, with the help of an instrumented bicycle and pre-evaluated terrain, to define a torsional stiffness profile of each rider, and that allows us to personalize suspension tuning to the particular characteristics of one individual.
Given all the advances seen in the late days in terms of navigation, positioning and on-board electronics, such work is of crucial importance to future developments involving the optimization and the refinement of a bicycle system to particular or momentary needs, allowing also for fexibility and/or adaptability of one single bicycle to an extended array of possible uses.
Leonardo Sanches Lima
Category: Science, Research and Development