There have been countless innovations in rear derailleurs over the years. The ever-increasing number of sprockets, the introduction of indexed shifting, the addition of STI levers, clutches, and electronics, and more recently, wireless technology, the list is endless. Despite this, the basic shape has remained largely unchanged from the original parallelogram design pioneered by Tullio Campagnolo in 1949.1]

Soon, this may all change. According to a recent patent application by market leader Shimano,

the brand is looking to revamp this design.

In the application, Shimano states: "When a bicycle is riding over uneven terrain, the rear derailleur chain guide may strike rocks or the ground. Therefore, it is desirable to increase the distance between the rear derailleur chain guide and the road surface.

Simply put, the primary problem that Shimano is trying to solve is the clearance between the derailleur and the ground. Naturally, this implies innovation in mountain biking, since road bikes rarely face such "uneven" terrain. The full bike diagram in the application affirms this assumption, but if this technology is commercialized and becomes popular, one might expect to see it spill over into gravel.

Shimano goes on to say: "It is also an object of this invention to provide a rear derailleur that can be applied to rear sprocket assemblies with a wide gear range.

Our understanding is that Shimano is trying to make a derailleur that can accommodate a wide cassette range, perhaps with a view to making the cassette range ever larger. Currently, the largest cassettes on mountain and gravel bikes have a range of over 40 teeth between the largest and smallest sprockets; given that one tooth is equivalent to one link of chain, the length of chain needed to use a 50-tooth sprocket, leave a lot of slack for the rider to replace with the smallest sprocket.

To counter this, the new design appears to maintain the parallelogram function, but instead of a cage extending downward from the upper pulley, there is a second cage that extends forward to the pivot point and houses two pulley wheels (three in total).

This second cage rotates in accordance with the position of the parallelogram, i.e., the gear the rider is in, to compensate for slack; how the second cage rotates is still a matter of debate. Shimano appears to be considering the use of a cable or wire-based system that would create a cam system to pull the second cage into position as the parallelogram changes position. Shimano has provided several diagrams of how this would work, with slightly different end results.

Aside from that, Shimano has included diagrams showing derailleur positions for various gears, as well as chainlines and routing.

In the image gallery below, the line marked 'C' on the diagram indicates the chain and the arrow indicates its direction of travel; the large circles from RS1 to RS12 indicate the cassette sprockets, and the three circles RA1, RA2, and RA3 indicate the derailleur pulley wheels

The other day, I took up the ...

Unlike Sram's three ridiculous patents we recently discussed, we do not know how far along the process of taking this derailleur from idea to reality is, or if it will ever go into production. What we do know is that this is not the first time a brand has considered rethinking the way bicycles shift gears.

Hub gears, for example, are already common in certain cycling segments, namely commuting, as Shimano's Alfine and Nexus hubs are ubiquitous in this area.

Ceramic Speed--which would be happy with the idea of a third pulley wheel, given that their main business is selling oversized ones--has a subsidiary called Driven that has been trying to reinvent the groupset with a driveshaft-based gearshift system for the past few years. In 2019, Shimano has again applied for a patent for a gearbox that places all shifting on the bottom bracket.

Other brands have tried their hand, and Belgian brand Classified has recently found success with a two-speed internal hub that can be combined with a traditional groupset, virtually eliminating the need for a front derailleur.