Despite the move to accommodate an MTB-style 10-51t cassette through the RX820-SGS rear derailleur, you’re not able to use one of
Shimano’s flat-bar trigger shifters.
The pull ratios on the 12-speed MTB components are longer and, as
Shimano’s David Lawrence told BikeRadar, the drop-bar shifter body would have had to widen to accommodate the longer pull ratio.
Whether this will pose a problem in the real world is debatable, however.
If you do want to flat-bar trigger shifters on your gravel bike, you could simply use one of
Shimano’s 12-speed mountain bike rear derailleurs (
SLX M7100,
Deore M6100,
Deore XT M8100 or
XTR M9100) instead, because they’re fully compatible with the new GRX RX820 cassettes.
As we’ll come to shortly, the ‘new’ GRX cassettes are
Shimano Deore XT mountain bike components anyway.