Rear Derailleur (2x)

Rear Derailleur (2x)


If you've been looking at GRX Di2 components you may have seen that there are two rear deraileurs. This RD-RX815 and the RD-RX817.

While the RD-RX817 supports a greater cassette range of 11-42T, that specific derailleur is not meant to be used with a front derailleur. It is the 1x-only GRX rear derailleur.

Affiliate Links

Using the affiliate links to purchase anything earns the site a small commission, at no additional cost to you.


So if you want to use GRX Di2 and run a front derailleur, this RD-RX815 is the way to go. It has a total capacity of 38T, with a top sprocket max of 11T and a low sprocket max of 34T (min 30T).

Both GRX rear derailleurs feature a clutch mechanism, just like the Ultegra RD-RX805 and the mountain bike rear derailleurs. Shimano call this the chain stabiliser. It can be adjusted and prevents chain slapping (or worse, dropping your chain).


  • Model code: RD-RX815
  • Series: GRX (RX815)
  • Weight: 287g
  • Speeds: 11
  • SD50 ports: 1
  • Max front difference: 17T
  • Total capacity: 38T
  • Low sprocket max: 34T
  • Low sprocket min: 30T
  • Top sprocket min: 11T
  • Top sprocket max: 11T
  • Pulley teeth: 13
  • RD type: Shadow RD+
  • Clutch: Yes

Related components

View the Rear Derailleur (1x) (RD-RX817)


Rear Derailleur (1x)

View the Internal Battery (BT-DN110)


Internal Battery

View the Front Derailleur (FD-RX815-F)


Front Derailleur

View the Hydraulic Disc Brake Dual Control Lever (ST-RX815)


Hydraulic Disc Brake Dual Control Lever

Related pages