While SRAM has stormed ahead with the release of their Eagle Transmission, it turns out Shimano too has been quietly working on a Direct-Mount Rear Derailleur of their own, as revealed by a patent published last June. First reported by BikeRadar, US Patent 20220204134 A1 describes and depicts a rear derailleur mounted to the dropout in a very similar fashion to the T-Type Direct-Mount Derailleur from SRAM; i.e., a hanger-less design with a mounting portion that occupies space on both faces of the drive-side dropout.
The patent document in question centers around the “bracket device” of the rear derailleur, and shows it in use with what otherwise looks like a regular mechanical rear derailleur. Let’s take a closer look.
The most interesting sentences of this Shimano patent, which are referring to that “bracket device”, are the following: “The frame attachment end has a first arm and a second arm, which are spaced apart in an axial direction with respect to the rear-wheel axis. The first arm has a first attachment opening through which the rear-wheel axis coaxially passes in amounting state of the bracket device. The second arm has a second attachment opening through which the rear-wheel axis coaxially passes in the mounting state of the bracket device”.
That’s a rather dry way of describing what can be seen in Fig. 2 and Fig. 7. These shed a bit more light as to why we’ve bothered sharing the contents of this patent document with you readers. Looks familiar, doesn’t it?
Indeed, the two-pronged attachment wraps the “bracket device” around each side of the dropout, and is secured in place by a threaded bolt running through the center. The design is not terribly dissimilar to SRAM’s Direct-Mount Derailleur that was released last week as part of their T-Type Eagle Transmission.
In Fig. 1, the rear derailleur is shown on what looks to be a mid-travel eMTB, suggesting the derailleur will find its home on a mountain bike, likely paired with a 12s cassette. In all instances, the derailleur is depicted as cable-actuated, unlike SRAM’s Direct-Mount offering which offers electronic shifting. Interestingly, the Shimano patent shows their mechanical direct-mount derailleur with use of a pulley wheel for guiding the cable to its clamp – a design more commonly associated with SRAM’s derailleurs.
Importantly, it looks as though this Direct-Mount Derailleur from Shimano will be able to accomodate different size cassettes. Labelled as 54 in Fig. 4, a screw is positioned around about where you might expect to see the B-Screw. The document describes this portion as the “angular position adjustment structure”. It serves to dictate the position of the rear derailleur relative to the frame and thus the sprockets of the cassette. Shimano’s Direct-Mount Derailleur also shows the usual High and Low Limit Screws in Fig. 9. These aspects are in contrast to the SRAM T-Type Derailleur which is designed specifically for use with a 10-52T cassette, and thus has no use for B-Screw.
Shimano’s patent touches briefly on how this design with its “bracket device” offers an improvement over existing designs, stating “The bracket device according to the first aspect reduces the amount of the rear derailleur projecting from an axial center plane of the bicycle and increases the rigidity of the rear derailleur. Further, the distance between a rear sprocket and the rear derailleur is easily adjusted and thus the usability is improved”.
A close-up of the SRAM Direct Mount Transmission Derailleur during installation
What isn’t clear from this filing is whether or not this rear derailleur design would be compatible with the SRAM UDH style dropout that has been almost ubiquitously taken up by frame manufacturers across the industry, and of course, whether or not it impinges upon the patents related to SRAM’s Transmission. Either way, it seems highly likely Shimano will eventually mount a response to last week’s big move from SRAM – there’s just no telling when.
No electronic version? It certainly looks as though there could be one in the works. As PinkBike reported, another Shimano patent that was published just last week describes a wireless electronic derailleur that appears to be Direct-Mount, too – though, the mounting style is really quite different to what we have so far discussed – it is actually more reminiscent of the brand’s original direct-mount offering seen on a 2013 SLX Group. Also, this electronic option is paired with a 9s cassette in the drawings, indicating it is most likely intended as part of a drivetrain for DH Bikes.