Shadow RD+ RX Rear Derailleur
The Ultegra RX Shadow RD+ rear derailleur is Shimano's first Di2 road rear derailleur with integrated chain stabilizer mechanism. It allows for a quieter experience and smoother shifting on mixed terrain. The chain tensioner or clutch can be switched off using the ON/OFF button, for rides on smooth terrain. It is a bit of a hybrid that sits somewhere inbetween the MTB and Road rear derailleurs - just like the GRX groupset.
So why does this derailleur exist you ask? It was developed and released a few years before GRX and provided a clutch mechanism for those who wanted to ride gravel on their road bikes.
It has a total capacity of 39T, with a max front difference of 16T. The largest sprocket max is 34T, the smallest low sprocket you can use is 28T.
On the other end of the cassette, the top sprocket max is 12T while the top sprocket min is 11T. Shimano are known to be a bit conservative with their min/max limits, so you can probably run a 36T/38T max and 10T top if you really wanted to.
The derailleur supports direct mount, but you can also mount it on a standard derailleur hanger.
- Max. front difference: 16T
- Total capacity: 39T
- Low sprocket: Max. 34T/Min. 28T
- Top sprocket: Max. 12T/Min. 11T