The proclamation “The king is dead. Long live the King” apparently dates back to 15^th Century France and was used when declaring the succession of a new monarch to the throne. After five years of sterling service, Shimano have decided to retire their old 11-speed GRX Di2 groupset and in its place comes a new 12-speed version, with the catchy moniker of RX825. If you’d like to find out all the details of the newest gravel groupset on the scene, then read on.

When Shimano launched the mechanical 12-speed version of their GRX groupset back in August last year, the rumour mill started swirling about when the electronic version would come out and trying to predict what technology it would feature. After today’s launch, we need no longer ponder the “I wonder what…” type questions as we have all the definitive answers. Here’s a summary of everything we know about the new RX825 12-speed Di2 GRX groupset:

• The new groupset is being launched in a 2x12 set-up only (with no news yet about whether a 1x12 version will be launched in the future….)

• The new groupset follows the precedent set by Shimano’s other electronic 12-speed groupsets in that the cockpit is now wireless, but the front and rear derailleurs are connected by a wire (albeit a smaller diameter version than before). 
• The wireless cockpit allows the use of satellite shifters for anyone considering running aero bars or wanting to use ‘sprinter’ buttons.

• The new RX825 shift levers have been “optimised for use on flared drop bars” with improved ergonomics, updated surface texture to the rubber hood and anti-slip coating on the levers. The levers have been re-designed to hold two CR1632 coin cell batteries which Shimano think will last between 3.5 and 4 years before needing to be replaced. The front of the shifter hood includes a battery level indicator light which changes colour to indicate the state of charge of the coin cell batteries. There’s a third Di2 button on the inside of the shifter hood which can be programmed to operate compatible bike lights, scroll through screens on a compatible bike computer or operate Shimano’s new ‘Front Shift Next’ function which “shifts the front derailleur to whichever chainring you are not currently using and then toggle back and forth.”

• The ‘brains’ of the system are in the RD-RX825 rear derailleur, which now contains the charging port, integrated Bluetooth d-fly connectivity and a multi-function button which “allows riders to easily check battery level, pair via Bluetooth, and enter adjustment mode for both derailleurs.”
• The front and rear derailleurs are powered by a “central, multi-port battery that supplies stable, long-lasting power.” In a change from the 11-speed GRX Di2 groupset, smaller diameter Di2 wires now “connect directly from the battery to each derailleur, eliminating the need for junctions and streamlining the build process”.

• The new 12-speed RD-RX825 rear derailleur is only compatible with Shimano's GRX820 31/48 tooth double chainset (not the GRX610 30/46 tooth double chainset) but it can be paired with an 11-34 or an 11-36 tooth hyperglide cassette.
• Anyone with existing 11-speed wheels using a hyperglide freehub body will be pleased to learn that the 12-speed 11-34 and 11-36 cassettes will fit perfectly, so there’s no need to buy a new freehub body.

As always, you can find out all the details of the new groupset over on Shimano’s website. 

If you’d like to get some of the background to the launch of the new GRX 12-speed Di2 groupset, check out our latest podcast episode, where our guest was Shimano Europe gravel category manager Erik Van Kooten.