Shimano 2x12 GRX Di2 Review

Shimano expands its gravel lineup. RX825 is the latest code of desire and refers to what has been expected since the launch of the mechanical 12-speed GRX in September 2023: a newest generation electronic GRX, now with twelve instead of eleven speeds.
Because the component giant primarily wants to serve the largest user groups first and globally the need for dual chainring cranks is significantly greater than that for single chainring drives, Shimano initially gave priority to the 2x12 option, as PR Manager Jonathan Davis explained to us.
“Specifically, riders with a road or racing background are demanding the dual version. Since the RX825 is based on technologies from the already existing road groups and is more race-oriented, it was quicker to develop and easier to introduce. 1x will come at a later date.”

Indeed, the 2x12-speed GRX should already offer suitable gearing options for gravel uses of various kinds - from leisure tours to races to multi-day adventure trips. Extensive options for individual configuration via additional switches and the E-Tube App (including shift intervals in Multi-Shift mode, assignment of functions to individual shift buttons, parameters for Synchronized and Semi-Synchronized Shift) complement the package.

The new Di2 group with Hyperglide+ technology for smooth shifting includes revised Dual Control shift/brake levers for optimal comfort and controllability, a Shadow RD+ rear derailleur for secure chain management, and a gravel-optimized front derailleur for precise shifts from the large to the small chainring and vice versa.
Or to put it another way: Take the already existing cranks, cassettes, and brakes of the RX820 series and combine them with the new Di2 shift levers including appropriate satellite switches, front derailleur, and rear derailleur of the GRX 825.

Like its mechanical counterpart, the preferred gearing can be achieved, for example, by choosing the 820 crankset with 48/31 teeth or the RX610 variant with 46/30 teeth, and either an 11-36 or an 11-34 teeth cassette at the rear.
Shimano recommends the current carbon models of the WH-RX880 series with a 25 mm internal rim width and updated Direct Engagement freehub bodies as suitable wheels.

For the power supply of the rear derailleur and front derailleur, the electronic 2x12 GRX, like its 12-speed siblings from the Dura Ace, Ultegra, and 105 Di2 series, relies on a cable connection to the central battery. The direct connection to the multi-port battery makes junctions unnecessary and simplifies installation.
According to Shimano, the centralized and wired power supply reduces the complexity of charging processes or different charging states of individual components. At the same time, stable power supply is ensured even under high mechanical stress in rough terrain.

The cockpit, likewise analogous to the latest road groups, is wireless and powered by two button cell batteries with a lifespan of up to 4 years.
As already with the RX815 predecessor models, the third Di2 shift button mounted on the inside of the horns ensures that for the control of additional functions – e.g., supplementary shifting, scrolling through the menu pages of a compatible computer, lap counter – the hand does not have to leave the secure grip on the handlebar.
Moreover, by expanding the system with additional switches on the top bar, lower bar, or aero extensions, athletes can select the optimal gear in all conceivable grip positions without having to change their grip. These additional switches can also be assigned numerous other functions via the app, in addition to gear shifting.

For off-road use, the cockpit is designed such that the bar ends are significantly raised and feature a ribbed surface. Slip-resistant brake levers also ensure safe operation at all times, and of course, the new Dual Control levers, weighing 415 g/pair, integrate well into handlebars with flared ends.
With a somewhat rounded shape, the transition from the handlebar to the STI bar ends is seamlessly designed and also increases the grip area, which should reduce the risk of pressure points.

Also known from the world of road biking: The actual communication center for the system is the 310 g weighing rear derailleur. That's why the charging port for the central battery and a multifunction button for checking the charge level, establishing a Bluetooth connection, and selecting the adjustment mode for the rear derailleur and front derailleur are also located in the rear derailleur.
The RX825 rear derailleur features the Shadow RD+ technology with the special "Clutch" mechanism. This mechanism, when engaged, locks the derailleur cage and is designed to prevent the chain from slapping, which reduces noise and the risk of the chain coming off. For easy removal and installation of the rear wheel, the mechanism can simply be switched off.

The front derailleur weighs in at 142 g. The chainline remains offset by 2.5 mm compared to road groups to ensure space for wide tires.
By the way: The introduction of the RX825 coincides with the debut of a brand-new shifting function called Front Shift Next. Available via a firmware update in the future, any Di2 button can be assigned through the E-Tube Project Cyclist App to all 2x12-speed systems, including current road groups, to shift to the currently unused chainring and back again. If the chain is on the big ring, the button shifts to the small one; if it is on the small ring, the same button shifts to the big one. The result is even faster, more intuitive shifting operations and the possibility to assign the thereby "freed" button on the STI to any other function.

In line with the GRX release, Shimano presents through the accessory label Pro a carbon handlebar plus aluminum stem for the fast among the gravel addicts, as aerodynamics is becoming increasingly a topic in this segment.
The Discover Aero Carbon available in three widths (40/42/44 cm) features a compact 100-mm drop with 12 degrees flare, meeting aerodynamically optimized tops with a downslope for a neutral hand position and a 4° sweep forward, for a more aerodynamic body posture.
Good control is ensured by the 12-degree bend, while the ergonomic curve at the drops considers the integration of shift levers and brakes, ensuring easy shifting and braking even on the roughest gravel terrain.

The UD T700 carbon construction of the handlebars with strategically placed Dyneema fibers is designed to offer excellent compliance and reduce vibrations, which are known to decrease fatigue during rides.
Both electronic and traditional cable-operated shift cables and hydraulic brake hoses are hidden from the wind at points where they would otherwise cause resistance, but are accessible to mechanics for maintenance purposes.
The weight varies depending on width from 265 to 285 grams. The Discover Aero Carbon is compatible with the Pro Compact Carbon Clip-On Aero Extensions.

The name of the corresponding stem comes from the +/- 10 degree angle at which the Discover Stem 10 can be tilted. It is made from an AL 7075 alloy using 3D forging and CNC manufacturing processes and is available in seven lengths from 60 to 120 millimeters (weight: from 142 g) with a standard clamp diameter of 31.8 mm.
Compared to the existing Pro Discover stem, which has an angle of +/- 6 degrees, the new one allows for an even more perfect adjustment to the bike and rider – which, according to product developer Mark Kikkert, weighs more than the sleek appearance of a fully integrated cockpit. Especially in the Discover product line, which is particularly aimed at comfort and control.