The bicycle is the most effective non-assisted form of displacement; thus, it has been extensively used as transportation vehicle, but also as a device for leisure and/or sportive competition. The different gearings in bicycle transmissions allow to comfortably ride on uphill or downhill terrain; indeed, there is a long-standing challenge to get the maximum gear range (large variation between the easiest and hardest gears in order to access a wide set of terrains) with minimum steps between gears (small variation between consecutive gears in order to adjust for a more consistent and efficient pedalling), i.e. the maximum number of effectively usable gear combinations is sought.
Since parallelogram derailleurs were introduced in the 1950’s, little changes have been observed in bicycle transmission technology. Even the most recent electronic derailleurs use the same parallelogram mechanism, just substituting the cable actuation by a motor actuation. There were high expectations that electronic shifting would bring sequential shifting, i.e. instead of the rider deciding whether to shift sprockets or chainring, a simple “harder” or “easier” transmission command would be provided, and the system would automatically operate on the corresponding sprockets or chainring, but it never happened.
The main challenge for improved gearing at present is still mechanical, as it was the case 60 years ago; i.e. pedalling force must necessarily be reduced if a front shift is going to be performed. The physics behind this issue are unavoidable: applying force on the pedals originates tension on the chain at the point where it engages the chainring, generating a downforce that keeps the chain firmly engaged. This is counterproductive for chainring shifting where a lateral force is applied by the front derailleur to disengage the chain in the upward direction and laterally displace it. In current transmissions, even when the chain is displaced under moderate tension, shifting results in high friction and is abrupt, and requires a high-powered motor to exert the necessary shifting force.
Therefore, as the problem is generated by trying to move the tensioned chain towards the chainring, the solution can be as simple as moving the non-tensioned chainring towards the chain. On the contrary, SEGSEQ segments can be displaced with no friction by low-powered actuators while they are on the “chain-free zone”, and they smoothly engage with the chain as pedalling rotation progresses. In this manner, the benefits of a smooth and reliable shifter can be fully exploited: shifting can be applied more often so that wide range and close-step transmissions can be designed for better performance. Also, as shifting is smooth during any situation (even under high pedalling loads), sequential or even automatic shifting are straightforward to implement for unprecedent ease-of-use.
