Electronic Shifters & Derailleurs for Road and Mountain Bikes

Advantages over Mechanical Shift Groupsets

The obvious advantage of electronic shifters and derailleurs is that you don’t have to worry about Bowden cables. This applies to the assembly process, adjustment, maintenance and wear, and makes a lot of things easier. Cables or wireless connections do not need to be readjusted or replaced regularly. Once set up, they provide you with constant shifting precision. You press buttons to change gears: they do not have long lever travel, do not require a lot of force to operate and their mechanics won’t wear out from exposure to dirt. Motors in rear derailleurs and front derailleurs do the bulk of the work with consistent speed and power every time. With some systems, you can individually set which buttons shift up and down. Optional extensions allow you to shift from other positions on the grips – such as on the upper handlebar or aerobars on your road bike. Of course, electronic shifting systems also offer connectivity. They can communicate with your bike computer or with apps on your smartphone. The added advantages range from simplified configuration to real-time information and detailed evaluation of collected data. The shifting system’s actuators require energy – connected devices can help you keep an eye on battery levels and remind you to recharge at the right time.

Simplified Shift Logic with or without a Front Derailleur

In groupsets with multiple chainrings, the electronically-controlled front derailleur can take the chainline into account – namely the current position of the chain on the cassette. If your chain is on a large sprocket, for example, the cage does not have to be moved as far to shift from the large to the small chainring as if it were further to the right on a small sprocket on the cassette. Over-shifting is thus effectively avoided. The derailleur guide plate can also always be aligned so that the chain does not drag or rattle. If you’d like, you can leave it up to the electronics to change the front chainring when shifting. You then only shift linearly up or down – without thinking about whether it is the front derailleur or rear derailleur or both. When changing the chainring manually, the rear derailleur can automatically counter-shift a few sprockets so that the jump in gear ratio is not so high. If you prefer, you can also shift gears completely manually. Even if you ride single-speed drivetrains with “only” one chainring, you benefit from the improved shift logic of the electronics, which effectively prevents over-shifting on the sprocket set or is able to jump several gears if necessary.

Shimano Di2: Overview

Shimano's electronic shifting system has been on the market longer than any other, and is known for its precision and fast response. The abbreviation Di2 stands for "Digital Integrated Intelligence". For mountain bikes, you have the choice between two top groupsets – the Shimano XTR Di2 and the XT Di2. The two highest-quality groupsets for road bikes are also available in electronic versions: Shimano Dura-Ace Di2 and Ultegra Di2. The GRX Di2 can be installed on gravel bikes.

Shimano Di2: Cable Routing and Power Supply

Whether it’s on a mountain or road bike, cables connect the actual shifting components on the Di2 with two distributors and a battery that supplies the entire system with power. The first distributor (Junction A) can be found in the form of a small box under the stem, as an information display on the handlebars of your mountain bike or inconspicuously hidden in the handlebar end of your road bike. The signals from the shift levers converge here, and it’s also where the charging socket for the system is located. The status LEDs, the information display, a connected bike computer or the app on your smartphone notify you when the battery should be charged. To connect the computer or smartphone wirelessly, you need a groupset with an information display or a separate D-Fly wireless module. A cable runs from the first distributor to the second, which is mounted on or in the frame – namely Junction B. The battery is connected here, which is also on or in the frame. It can remain there for charging. Junction B then controls the rear derailleur and front derailleur, which in turn are connected via cable. By the way, the individual cables are interchangeable, but should be the correct length. The better your frame is prepared for Di2, the easier it is for you to lay the cables and install individual components. Unlike with shift cables, you only have to do all this work once.

In September 2021, Shimano relaunched the Dura-Ace and Ultegra groupsets and has since relied on wireless technology. The cable connection between STIs and rear derailleur is eliminated. The rear derailleur receives the signals from the STIs and passes them on to the front derailleur via a cable. Both the rear and front derailleur are connected to a battery that is installed in the seat tube.

SRAM AXS and eTap AXS: Ergonomics

SRAM’s electronic groupsets for mountain biking come with a rocker switch that can shift up and down. With the help of the AXS app, you can set which button shifts in what direction. If you install the RockShox Reverb AXS telescopic seatpost, which is also controlled wirelessly, there is another switch on the left side of the handlebars that operates the post in the default setting. A nice thing about this: the switch on the seatpost is compatible with other functions – you can also programme it to control the shifters & derailleurs. You could then control the seatpost with one of the buttons on the right side. The shift/brake levers in road bike groupsets have only one button each. One hand shifts up and the other down – you can decide which. In "Sequential Shift Mode", the front derailleur is shifted automatically. In manual mode you shift the front derailleur by pressing both buttons simultaneously. Optionally, the “Compensating Shift Mode” then ensures that the rear derailleur automatically shifts one or two sprockets to keep the jump in gear ratio as low as possible. You can also configure how many gears your AXS derailleur changes when you press and hold a switch in the app. With added-on Blips or MultiClics shifters, you can expand the system and, for example, shift from the top handlebar or aerobars of your road bike. You can connect the extensions directly with cables to the shift/brake levers of the top Red and Force groupsets. The entry-level Rival groupset can only be expanded to a limited extent. To use them with additional switches, you need a BlipBox, as the shift/brake levers do not have a connection. In contrast to Red and Force, several switches cannot take over the same function. For triathlon or time trial bikes, there are the Zipp Vuka Shift AXS 90 aero extensions that directly integrate the system. You should always observe specifications for compatibility. Current AXS components and extensions are compatible between groupsets but will not work with older eTap systems.

Campagnolo EPS: Overview and Ergonomics

Campagnolo’s electronic road bike groupsets also operate using cables. The system goes by the abbreviation EPS (“Electronic Power Shift”) and is currently used in the top Super Record groupset with 2 x 12 speeds. As with Campagnolo’s mechanical groupsets, the EPS Ergopower shift/brake levers are operated with a switch on the brake lever and a thumb switch on the inside of the hoods. With the help of the “MyCampy” smartphone app, you can read data and adjust the ergonomics individually. You can select different shifting modes with alternative button assignments and also operate the system one-handed, for example. The “Shift Assist” option compensates for the large jump between the chainrings by compensating shift increments on the rear derailleur. With “Multishifting” you can select the maximum number of gears that are shifted when you hold the switch down and how long you have to hold it down for to do so. Campagnolo gives you the option of adjusting the front and rear derailleurs in three stages, how smoothly or aggressively and how fast the motors shift. The “Race”, “Sport” and “Comfort” shift modes let you choose from preset profiles that differ in the aforementioned parameters. The new "Sequential Shift" function offers a mode that completely automates the interaction between the rear derailleur and front derailleur. You just shift into a higher or lower gear and the system takes care of the rest. With EPS bar-end controls, you can expand the system with additional switches and also trigger shifting operations from the aerobars.

Electronic Hub Gears

In addition to derailleur gears, Shimano also offers two electronic internal hub gears. For an everyday or touring bike, you can opt for the Alfine Di2 with eight or eleven gears. As with derailleur gears, the gear hub is controlled by distributors and the system is powered by a central battery. The E-14 electronically shifting gear hub from Rohloff is currently only available on fully-assembled e-bikes and cannot be retrofitted. However, the system shows where the journey can lead: by accessing the engine control unit, the system reduces engine assistance when shifting gears or, if desired, automatically engages a lighter gear for starting back up again after stopping at traffic lights.