Shimano is developing a new axle-mounted Di2 wireless derailleur and it could be released soon

It looks like we will be saying farewell to the derailleur hanger in the near future as Shimano appears to be following SRAM's lead and developing their own axle-mounted derailleur. 

Recently we have seen a lot of development when it comes to the best MTB drivetrains, with the biggest news being SRAM putting the first nail in the derailleur hanger coffin with its T-Type hangerless transmission and TRP updating their EVO groupset too. In patent applications filed by Shimano and first reported by Bike Radar, it looks like Shimano is working on a major MTB groupset update.

RIP the derailleur hanger

While SRAM described their new transmission as having an entirely new hangerless interface, Shimano actually beat them to the punch with the axle-mounted Hone / Saint / Zee groups all the way back in 2003. It didn't catch on, probably because most bikes were still running quick-release axles back then, rather than thru-axles.

The patent appears to show a couple of different attachment methods, but both are essentially the same and mounting the derailleur to the axle, rather than the frame. It's not just about a stronger mounting point for better shifting, by “coaxially” mounting the mech with the cassette adjusting the derailleur should be considerably easier too. Don't take our word for it though, here is what the Shimano patent says:

"It is possible to adjust the bicycle rear derailleur via the controller to a position that may be advantageous to the use of the bicycle on different types of terrain and through varying riding conditions. The controller may control the motor to make position adjustments to the bicycle rear derailleur. The first wireless communication unit may receive input from the user controlling a remote component that directs a change in a position of the bicycle rear derailleur."

Very exciting stuff I'm sure you will agree.

How it differ from SRAM's T-Type?

It appears that Shimano is taking a similar approach to SRAM to mount to the axle, with two arms with "a radial thickness of at least 2mm" sandwiching the frame. Whether this will be compatible with SRAM's UDH (Universal Derailleur Hanger) standard is unclear, although this could be a major point of contention between the two drivetrain giants. 

SRAM released its UDH as a better hanger system and there was good uptake from the industry due to its simplification of frame hardware. However, it appears to have also been a ploy to insure there were more bikes that would be compatible with the T-Type transmission. If Shimano is unable to use the same derailleur fitment then they will need to come up with an alternative that will be easily adopted by frame manufacturers.

SRAM has removed all adjustment screws on the derailleur but one big feature depicted in the Shimano patents is the B-tension screw. This is used to adjust the position of the derailleur in relation to the cassette meaning the derailleur could be used with different size cassettes, unlike the SRAM system which can only use the 10-52t Eagle cassette.

Return of Di2 to MTB

While the demise of the derailleur hanger is a notable new chapter in mountain bike history, so is the possible return of electronic shifting to Shimano's MTB range. Shimano brought Di2 to MTB back in all the way back in 2014 which, funnily enough, followed shortly after SRAM's release of AXS.

SRAM has invested a lot of focus into electronic shifting, releasing multiple iterations of its wireless MTB groupsets and filtering the technology to its mid-tier GX AXS groupset. Shimano's Di2 groupset, on the other hand, was only updated once in the form of M8050 Di2 in 2016 before being seemingly abandoned.

This new patent gives hope that Shimano will once return to electronic shifting and bring MTB Di2 out of the 11sp era and give it a 12sp update. It's likely to be more significant than simply removing the derailleur hanger and adding a sprocket to the cassette. Although MTB Di2 has stagnated, Di2 on the road has some recent updates, moving to a less-wires system as well as filtering the technology down to the mid-tier 105 level.

It's not been radio-silence on the MTB drivetrain front mind you, Shimano released an e-bike-specific 12-speed XT Di2 drivetrain last summer. Featuring some neat tricks like a cadence, velocity, and acceleration sensor that can be used for shifting, both manually and automatically.

There is a good chance that the new MTB Di2 will be fully wireless too. The current road Di2 uses a semi-wireless system, with the derailleurs connected to a central battery stored in the seatpost, wireless shifters, and the full system being controlled by the rear derailleur. The patent specifically states that “it is possible to mount a battery for the electronic components of the bicycle on the rear derailleur, which may also be to power electronic derailleur control". This could indicate the MTB Di2 will move away from a frame-mounted battery and any need for wires.

When will we see this tech on our bikes?

Considering this patent surfaced shortly after SRAM's T-Type release, the likelihood of seeing this tech hit the market is extremely high. 

We suspect a new Shimano drivetrain will be released before the end of the year considering the significance of a shift in drivetrain design by SRAM, Shimano's four-year drivetrain development cycle, and the fact that Shimano hasn't updated XT M8100 since the move to 12-speed in 2019.