Thursday, January 11, 2018

Shimano Dura-Ace Road Hydraulic Mechanical Shifter ST-R9120

Road hydraulic disc has been gaining popularity in the recent years. With improved braking performance and modulation, it is no wonder that more riders are choosing to go with hydraulic disc brakes instead of conventional caliper rim brakes.

As such, the types of road shifters used must also evolve to match the new braking system. There are two types of shifting systems: Mechanical shifting which uses steel inner cables to activate the front and rear derailleurs, and electronic shifting that uses electrical signals to activate the motors in the front and rear electronic derailleurs.

Today's post will be about mechanical shifting together with hydraulic disc brakes. For such a road shifter, it will need to incorporate the shifting mechanism as well as the hydraulic brake mechanism within the road shifter. This is a big challenge as these parts take up space and it is hard to squeeze both of them into the limited space of the road shifter.

For Shimano, the first generation of such a shifter is the non series ST-RS685, more details which can be found at this post created two years ago. Now, there is an official Dura-Ace version of such a shifter, which has a model number of ST-R9120. This is the second generation design, therefore it will be more refined and probably with significant improvements.

Let's take a look at this Dura-Ace ST-R9120 road shifter, which is used for mechanical shifting and hydraulic disc brakes. A detailed comparison with the first generation ST-RS685 will be made later in a separate post.

ST-R9120, weighs 265 grams for one side. A pair will thus weigh 530 grams, which is significantly heavier than the rim brake version which is 365 grams per pair.

With the rubber hood stripped off, the Bracket of the road shifter can be seen clearly. This is the "outside" which is facing the outside of the bicycle.

The "inside" of the shifter.

The biggest difference from the first generation ST-RS685 is that the Bracket material has been changed from aluminium to resin for weight savings.

The front part of the shifter is where the reservoir is located, with the "piping" for the hydraulic fluid machined within the resin Bracket. Bleeding port is located on top.

The rear of the shifter where the hydraulic hose will be connected. Note that this thread is a special M9x1.25 size! Not the usual M8 x 0.75 thread. Clamp band is made of titanium.

Rubber damper for the lever is inserted from the side. Other cutouts are there to secure the rubber hood onto the Bracket.

Similar to other mechanical shifters, the inner cable is inserted from the side. Bracket is made of nylon with a mix of carbon fibre for strength. Silver bolt on top of the Bracket is for adjusting the free stroke, although the adjustment range is very small.

Lever mechanism is similar to other road shifters, while the steel plates now have a black surface treatment instead of silver colour.

Bolt in the centre is used to adjust the reach of the lever, which is separate from the free stroke adjustment.

Without dismantling the shifter any further, this is all that can be seen from the outside. On its own, it is quite amazing that both the shifting mechanism and the hydraulic mechanism has been squeezed into this road shifter without making it too bulky. In a separate post, this new ST-R9120 will be compared to the ST-RS685 to see what has been changed from the first generation.


  1. Thanks!
    The thread size info posted here was a life saver :)

  2. Very detailed review with some good pictures. Question: I stripped the female threads in the resin body for the hydraulic hose connector on my right side shifter during installation. Will I have to replace the entire shift lever assembly?

    1. Unfortunately yes, because the threads are part of the resin bracket.

    2. Thanks, that's what I thought... an expensive mistake that I will not make twice.