Shimano Road Hydraulic Disc Brake Di2 Shifters: ST-R9170 vs ST-R785

After comparing the mechanical shifting versions, I will now compare the Di2 versions of the road hydraulic shifters. The non series, first generation, Di2 shifter with hydraulic braking is the ST-R785, while the latest second generation is the Dura-Ace ST-R9170.

For Dura-Ace components, being lightweight is very important. Having the best function is also required. In this case, the shifter was totally redesigned to create the new ST-R9170, as compared to the ST-R785.

New Dura-Ace ST-R9170 weighs only 160 grams per side, giving a total weight of just 320 grams per pair.

Non series ST-R785 weighs 254 grams per side, giving a total of 508 grams per pair, which is significantly heavier.

Rubber hood has a different texture, with the "waffle" pattern used on the new ST-R9170 (right side).

Comparing the side profile, the ST-R9170 is obviously lower in height, which makes it look much more similar in shape and size to the other Dura-Ace road shifters.

Dura-Ace ST-R9170 is lower in height, while the lever shape is also curved outwards to match the other mechanical road shifters.

ST-R9170 on the left looks very similar to other road shifters, while ST-R785 has a large silver cover which gives it a very distinctive look.

ST-R9170 on the left has slightly larger Di2 buttons and a stronger click feeling, for an improved tactile feel.

Rear of the lever is where the mechanism for the buttons are housed. ST-R9170 on the right has a cleaner look as the parts are all black in colour and more concealed.

ST-R785 on the left has a lever stopper on the Bracket, while the wire can also be seen. ST-R9170 improves on these with a reach adjustment bolt at the bottom and hides the wire, while the rubber hood texture has also been changed.

Rear view shows that the new ST-R9170 (right side) has a wider Bracket, and uses a titanium Clamp Band for lighter weight.

Internal profile of the ST-R9170 rubber hood. Due to the multiple protrusions as shown, and the many ribs on the Bracket, it was very difficult to remove and install the rubber hood.

ST-R9170 on the left has many ribs on the resin Bracket for weight savings, while ST-R785 on the right uses an aluminium Bracket.

The Di2 unit is smaller in size on the ST-R9170 (left side), while it is also located more rearwards for easier access. Also note the different wire routing through the Bracket.

Another major difference is the pivot location of the brake lever. ST-R785 on the left has a high pivot, while ST-R9170 has a pivot location that is lower and similar to other mechanical or Di2 road shifters. This allows the brake lever ergonomics to be similar to other Dura-Ace shifters.

The bleeding port for ST-R9170 (left side) is located in the middle of the Bracket (black bolt), while the ST-R785 bleeding port is right at the front of the Bracket. The little bump at the front of the ST-R9170 bracket is the top button which can be programmed.

This side by side picture shows how different the Bracket design is, as well as the different hydraulic design.

This new generation ST-R9170 is a significant improvement over the first generation ST-R785, with the major improvements being lower weight, smaller size, and a more conventional braking ergonomics. There is also an additional button on top for extra customization.

Shimano Road Hydraulic Disc Brake Mechanical Shifters: ST-R9120 vs ST-RS685

There has been two generations of road hydraulic shifters, with the first being non series, and the latest being part of the Dura-Ace series. For the mechanical shifting version, the first generation ST-RS685 is now used on many cyclocross bikes or road hydraulic disc bikes. The improved, second generation version is the Dura-Ace ST-R9120 which is engineered to be more lightweight.

ST-RS685 weighs 324 grams per side, giving a weight of 648 grams per pair. This is heavy, mainly due to the aluminium Bracket.

ST-R9120 is lighter in weight, weighing 265 grams per side, for a total weight of 530 grams per pair.

Release lever of ST-R9120 on the right has been slightly increased in size for easier activation.

ST-RS685 on the left is non series, with the Shimano logo on the lever. The new ST-R9120 on the right has the Dura-Ace logo, with a superior surface finishing.

View from the front shows that the curve of the lever is similar, but the ST-R9120 has a slightly wider lever shape near the top.

The hood shape is slightly different, with ST-R9120 at the front having a more rounded hood that is slightly lower in height.

From the front, the difference is obvious. ST-R9120 on the right is lower in height but slightly wider, which gives the impression of a smaller hood size.

Inside view of the Bracket. ST-R9120 on the right uses a resin Bracket, and you can see the cylindrical shape of the hydraulic system.

Rear view of the shifters show that the ST-R9120 on the left is slightly wider in size but also shorter in height.

Upon removing the rubber hoods, more differences can be seen. ST-RS685 on the left has an aluminium Bracket, while ST-R9120 on the right has a resin Bracket.

View from the other side. ST-RS685 uses metal pipes for the hydraulic system, while ST-R9120 on the right does not.

From the top, we can see that the new ST-R9120 on the right has the piping concealed within the resin Bracket, instead of being separately created via metal pipes.

ST-R9120 on the left has a different thread size, which is M9x1.25. This is different from the standard M8x0.75 that is used on other most Shimano brakes.

Main difference between these two shifters is the material used for the Bracket, which directly affects the weight. The hydraulic design has also been tweaked to eliminate the need for metal piping, and instead route the hydraulic fluid within the resin Bracket itself. All these improvements lead to weight savings and also a smaller overall size.

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.

Canyon Endurace: Dura-Ace Road Hydraulic Di2 Shifter ST-R9170

There are 4 types of road shifters in the new Dura-Ace R9100 series. With two types of shifting (mechanical or electronic), and two types of braking (rim or hydraulic brakes), it gives 4 different combinations, which will suit anyone regardless of your shifting or braking preference.

The most premium combination is the electronic shifting, hydraulic disc brake version, which has the model number ST-R9170. Combining Di2 shifting with road hydraulic disc, it features effortless shifting and braking. Also, it is the only version not to use any steel inner cable for shifting or braking. Replacing the shifter inner cable is the Di2 electrical wire, while replacing the brake inner cable is the hydraulic brake hose.

These shifters will be replacing the non series ST-R785 that came with the Canyon Endurace road bike. The ST-R785 is the first generation of Di2 shifting/hydraulic braking road shifter, while this Dura-Ace ST-R9170 is the second generation. My plan all along was to upgrade the groupset to a full Dura-Ace groupset, from the stock Ultegra Di2 6870 groupset that came with the bike.

Handsome looking Dura-Ace ST-R9170 road shifters, with a very high quality finishing on the levers.

Another view of the new shifters. The lever shape has been subtly refined from previous generations.

Overall shifter shape is very similar to other shifters in the same Dura-Ace R9100 series, which is done by totally redesigning the shifter.

Another overall view of the ST-R9170

Due to the resin Bracket construction, the shifter weighs only 160 grams per side, giving a total weight of 320 grams per pair. This is very lightweight!

The Di2 shifter buttons have been increased in size compared to older Di2 shifters. The clicking feeling has also been enhanced for a better tactile feel.

Electronic button unit looks to be quite well integrated into the lever.

This textured area at the top of the hood hides a button underneath! This button can be programmed to perform shifting functions or control other devices such as the Garmin computer.

Hydraulic hose attaches to the rear of the shifter. Titanium clamp band for weight savings.

From the outside, the shifter looks very ordinary, as the rubber hood hides all the interesting bits underneath. However, once the rubber hood is removed, it looks much more interesting!

With the hood removed, the Bracket design can now be seen. The small box is where the Di2 wire will connect to. This box is linked to the top button by a wire...

...while the top button is linked to the shifter buttons below by another wire running through the area shown above.

Bleeding this hydraulic shifter requires an adapter (included) to enable the standard bleeding cup to reach the bleeding port on the shifter. This is because the bleeding port on the shifter is located on top, in a recessed area.

Slot on side of Bracket to guide the cam of the hydraulic piston, for a Servo-wave effect.

One thing you notice is how many ribs are used to strengthen the Bracket and yet keep it lightweight! This is only feasible as a molded resin bracket (nylon + carbon fibre) is used. These ribs also make removing and replacing the rubber hood very difficult.

Located at the bottom of the shifter are the free stroke adjustment bolt (on right) and the lever reach adjustment bolt (on left).

Hydraulic piston slides along the internal bore of the Bracket when the brake lever is activated.

A quick comparison of the new Dura-Ace ST-R9170 with the older ST-R785. The lever shape is noticeably different, with the Dura-Ace lever having the same curved shape as the mechanical road shifters.

The new Dura-Ace shifter is also lower in height, which makes the new shifter look much smaller in size. This is possible only due to a new hydraulic brake design.

In a separate post, the ST-R9170 and the ST-R785 will be compared in greater detail. From what I can see, the main differences by making this upgrade is a slimmer looking shifter and also lighter weight. Ergonomics will be similar to other road shifters with Di2 or mechanical shifting, while the tactile feeling of the Di2 buttons will be improved.