GRX Rear Derailleur: RD-RX815 vs RD-RX817

For the new GRX groupset, there are a total of 4 derailleurs, as shown in the picture below. There are 2 mechanical rear derailleurs and 2 Di2 (electronic shifting) rear derailleurs.

The 4 types of GRX rear derailleurs available.

I am using the GRX RD-RX815 Di2 rear derailleur on my Canyon Endurace for gravel riding, and you can read all about it here. Let me just explain briefly what are the differences between these rear derailleurs.

There is a 1x11 and 2x11 speed spec. The 1x11 speed spec has a shorter cage, and a greater slant angle, in order to shift across the wide ratio cassette (up to 42T sprocket). The 1x11 speed spec cannot be used for front double systems, as the chain capacity is insufficient. This 1x11 speed spec is very similar to the MTB version of Di2 rear derailleur (such as Deore XT RD-M8050), as it is used for wide ratio MTB cassettes.

On the other hand, the 2x11 speed spec is quite similar to road rear derailleurs, like the Ultegra RD-R8050. It has a longer cage to cater for the combined chain capacity of the front crankset and rear cassette. However, the max rear sprocket size is limited to 34T, as 1) Not enough chain capacity for larger sprocket, and 2) Shallower slant angle, unable to reach larger 40T or 42T sprocket.

Of course there are those who will try to set up the rear derailleurs beyond these recommended specifications, and they may work, depending on how you adjust it. However, the shifting performance may suffer.

Then, there is the mechanical spec and Di2 spec. All the above information applies to both the mechanical and Di2 spec. In summary, there will be a suitable rear derailleur for you, regardless of whether you use mechanical or Di2 shifting, or whether you are using a front single or front double drivetrain.

Needless to say, all these GRX derailleurs have a clutch system, for chain retention over bumpy terrain. This is the main difference between normal road and these gravel rear derailleurs.

For the detailed comparison below, I will be using the Di2 versions for comparison, the RD-RX815 (2x11 speed Di2 spec) and RD-RX817 (1x11 speed Di2 spec).

RD-RX815 (2x11 speed, longer cage) on the left, and the RD-RX817 (1x11 speed, shorter cage) on the right.

The design language may be similar, but the construction is quite different.

RD-RX817 (right side) has a larger motor, which is from the Deore XT Di2 rear derailleur.

The clutch design also looks different. RX817 on top, RX815 below.

RX815 on the left, with a black clutch lever. RX817 on the right has a grey coloured clutch lever.

RX817 (top) has a rubber cap, which protects the external clutch adjustment screw from dust and dirt. For RX815 (bottom), you have to remove the plastic cover for clutch tension adjustment.

The construction is also quite different. RX817 (top) has a stamped aluminium inner link, while RX815 (bottom) has a resin inner link.

Motor unit and the surrounding link arms are very different as you can see.

The design of the saver unit is also totally different. RX817 on the left, RX815 on the right.

Both have a 11T guide pulley.

RX815 (right) has a longer cage for more chain capacity. Lots of cutouts on the inner plate for weight savings.

RX817 (left) has a 11T tension pulley, while RX815 (right) has a larger 13T tension pulley. This helps to increase chain capacity without further increasing cage length.

RD-RX817 (1x11 speed spec) weighs 321 grams, which is exactly the same as the Deore XT RD-M8050 rear derailleur.

RX-RX815 (2x11 speed spec) is a bit lighter, at 287 grams. However, this is still 90 grams more than the Dura-Ace RD-R9150 that I am using on the Canyon Endurace.

From this comparison, we can see that although both are GRX rear derailleurs, they are fundamentally different. The GRX 1x11 speed rear derailleur is a direct copy of the MTB version of the Di2 clutch rear derailleur, while the 2x11 speed construction is new.

Polygon Cozmic CX3.0: Shimano XTR M9100 1x12 Speed Drivetrain

I have been trying out different 12 speed groupsets on my Polygon Cozmic CX3.0 MTB, just to compare and feel the differences between them.

The S-Ride 1x12 speed was the first one to be tested, as it was the only upgrade available at that time (August 2018), because SRAM NX Eagle was not available yet. After that, the SRAM NX Eagle 1x12 speed upgrade kit was tested.

Finally we move on to the XTR 1x12 speed setup, which should work better than the other two 12 speed groupsets as it is the top of the range MTB groupset from Shimano. Let's try it out and see how it goes.

XTR RD-M9100 12 speed rear derailleur

There is no longer an extra adapter on the rear derailleur, like other Shadow type rear derailleurs.

Clutch mechanism, with the lever to turn it on and off.

Cable fixing bolt at the inner link of the rear derailleur.

View of the cage set. The guide pulley has a big offset from the rotation axle of the cage set, so that it can reach the larger sprockets of the cassette.

The 51T marking on the cage is useful for adjusting the B-tension, to maintain the correct distance between the sprocket and the guide pulley for optimum shifting performance.

Other than the 12 speed rear derailleur, a 12 speed shifter is also needed. At this point in time (July 2019), only the XTR 12 speed shifter was available, as Deore XT and SLX is not available yet.

XTR SL-M9100 12 speed shifter

The XTR logo is printed at this location, so that it is visible from the rider's point of view.

Both the main lever and release lever have a rubber pad for extra grip during shifting.

The initial design of this shifter has a switch for the user to select 12 or 11 speeds, as there was going to be a 11 speed cassette as well. However, the 11 speed cassette was later cancelled, and newer shifters no longer have this selector switch.

Slim clamp band and ergonomically placed shifting levers.

This time, I will only be changing the rear derailleur and shifter, while still using the 12 speed 11-50T S-Ride cassette and 12 speed YBN chain from the S-Ride groupset. This is because I am not able to use the 10-51T Shimano cassette, as a new Microspline freehub is needed.

At the same time, I decided to change to a new flat handlebar on the MTB, since I am changing out the shifter as well. This is a slightly wider handlebar that will improve the control on off-road trails.

PRO Koryak aluminium handlebar, with 720 mm width and a slight 8 mm of rise.

The guide lines for cutting the handlebar, if you need to shorten it. 

XTR 12 speed rear derailleur assembled on the bike!

Still using the old 12 speed 11-50T cassette and the 12 speed chain.

12 speed drivetrain! Front crankset is the SLX FC-M7000 with a 34T chain ring. As you can see the drivetrain is a mish-mash of parts from different brands and grades.

XTR 12 speed shifter installed, with the logo visible from the rider's point of view.

Still using the same old Deore M615 brake levers.

A picture of the MTB outside, while testing the new 12 speed setup.

Nice scenery of the CBD area, while along the Singapore River.

Another view of the bike.

The XTR 12 speed shifter and rear derailleur works well, but it will still mis-shift sometimes, I think due to the S-Ride cassette. The spacing between the sprockets does not seem to match the movement of the rear derailleur fully, as it is not a Shimano 12 speed MTB cassette.

Otherwise, the shifting feeling of the 12 speed shifter works really well, with very positive clicks during shifting.

Shimano RX8 Gravel Shoes - Silver Camo

As you may have realized from reading this blog that I am quite into gravel riding these days. The general idea of gravel riding is to ride light off-road trails on a road bike, and you can read a more detailed description here.

For gravel riding, most riders that use cleats will use SPD type of cleats, which are used for MTB and off-road riding. SPD-SL cleats which are for road bikes are hardly used for gravel riding, as the ability to walk properly is greatly compromised. Here is an article that I wrote some years back, but it is still as relevant. SPD-SL pedals and cleats also clog up more easily with mud, which will prevent you from clipping in normally.

I like to use SPD cleats and shoes, even on my road bike, as I want to be able to walk normally even when I am off the bike. I cannot do that if I use SPD-SL road shoes. Therefore, all my bikes either have a dual-sided SPD pedal such as the PD-M9020 or a SPD/flat dual sided pedal, such as the PD-A530.

The downside of using SPD shoes is that they are designed for off-road riding, which means there are large lugs on the sole, plus they use thicker and tougher material for off-road durability. This results in a shoe that is heavier and also looks too rugged for me.

I have previously used the RT82 Road Touring Shoe, which looks more like a road shoe but with SPD cleats. It works well, but it was discontinued a couple of years ago and I could not find a suitable replacement from Shimano.

After looking at other brands, I found a good looking one from Scott, which is the Scott MTB Elite Boa shoe. It looks less rugged, with nice colours and also has the Boa dial which makes it so much easier to put on or take off the shoe with one hand.

This year, the gravel dedicated groupset GRX was launched, and as part of the gravel setup, there is also a dedicated gravel shoe, the RX8 (SH-RX800). What makes it special is that it is a hybrid of road shoes and MTB shoes. Let's take a look and see what makes it so unique, and why I decided to get it.

RX8 Gravel Shoe!

Looks good! With a simple velcro strap at the front and a single Boa dial for adjustment, almost the same as the Scott MTB Elite Boa shoe.

RX8 logo clearly seen at the top. 

Very interesting silver camouflage pattern! Looks better in person and under sunlight. Very unique design.

Lots of holes for ventilation, we shall see how effective they are.

The Boa dial has a transparent cover, but I can't really see how the mechanism works.

The top part of the shoe looks very much like a road shoe, with the sleek and minimalist design with no seams.

SPD cleat mounting point, with printed lines that makes it easy to align the left and right cleats to the exact same position. The carbon sole stiffness is rated at 10 out of 12 which makes it really stiff.

Rubber lugs are small and of minimum size and height to reduce the weight of the shoe. Carbon shank extends throughout the whole shoe to make it stiff like a road shoe.

Shoes look really narrow but it fits well once the foot is inside.

There is an elastic strap that helps to wrap the top of the shoe over the top of the foot. However, it also makes it more difficult to wear the shoe.

The shoe weighs 284 grams, including the cleat nut (plate) but excluding the cleats and bolts. The claimed weight of 265 grams per side probably excludes the cleat nut weight.

Weight of the pair of cleats and bolts is 51 grams.

With the cleats installed. I fine tuned the adjustment on one side by repeatedly setting it and testing it, until I was happy with it. Then, I used the printed lines to replicate the setting on the other side.

With the cleats installed, one shoe weighs 309 grams.

In comparison, the Scott shoe weighs 416 grams, which is more than 100 grams heavier just on one side!

Comparing the weight, the RX8 is 25% lighter than the Scott shoe, which is very impressive. The total weight difference for a pair is more than 200 grams, which is quite a lot for just a pair of shoes.

That said, although I can feel the weight difference when holding the shoes, I can't really feel the weight difference when wearing it and pedaling with it. Let's do more comparison pictures to see how the RX8 differs from the Scott shoe.

Both are EU Size 42, but the shape appears to be totally different. Although the RX8 looks longer, it is just an illusion as the size is correct once the foot is inside. It fits my foot nicely with no need to increase or decrease the shoe size compared to my normal running shoes.

Both are using Boa dials that can be adjusted both ways for fine adjustments. The RX8 has two overlapping, asymmetric tongues, while the Scott has a traditional tongue in the centre, with the Boa wire passing through both sides symmetrically.

The RX8 looks just like a road shoe, compared to the Scott which looks tougher like a MTB shoe. The front part of the RX8 is also slightly higher to make it easier to walk with the stiff sole.

Rear view of the shoes. The RX8 has a stiff and supportive cup that fits my heel perfectly, to prevent it from slipping out even when the Boa dial is not fully tightened.

Front view of the shoes. The Scott has a "scuff plate" at the front to minimize damage to the shoe when walking off-road, while the RX8 does not, to save weight.

The soles look very different, as the RX8 has minimal lugs to simulate a road shoe, while the Scott shoe has many lugs spaced widely for more stable walking when off-road. There is an extra rubber layer in the middle of the RX8 to prevent the foot from slipping off the pedal if not clipped in.

The RX8 is a good looking gravel shoe, perfect for those who want to use SPD cleats, but want the appearance and low weight of a road shoe.

Highlights of this RX8 Gravel Shoe:
1) Lightweight, at over 100 grams lighter per side, compared to the the Scott MTB Elite Boa.
2) Easy to use Boa dial with two way adjustment possible.
3) Close fitting heel cup and tongue to cradle the foot securely.
4) Stiff carbon sole to improve power transfer, I can feel the difference when pedaling hard.
5) Great looking silver camouflage colour, and a nice road shoe appearance.
6) Appearance matches well with a road bike, but with SPD cleats for more walking convenience.

Issues I had with this RX8 Gravel Shoe:
1) Tongue of the shoe extends quite far back, making it a bit uncomfortable as the top of my foot is quite high. This makes the tongue "bite" into the top of my foot when the ankle is bent all the way up. Solution is to loosen the shoe slightly.
2) Elastic strap on the inside of the shoe makes it more difficult to insert the foot into the shoe.
3) Lugs on the sole can be placed slightly wider apart, to provide more stability when walking, as I have rolled my ankles a few times when the shoe rotated outwards when walking.
4) Stiff sole makes it less comfortable to walk compared to the Scott shoes.

Overall, this RX8 is a hybrid between road shoes and MTB shoes. It is mostly a road shoe, but with MTB SPD cleats and some lugs for ease of walking. This makes it lightweight (530 grams per pair), as it is just about 50 grams heavier than the top end RC9 S-Phyre road shoes (486 grams per pair). Weight is excluding any cleats or cleat nuts.

I am happy with this RX8 gravel shoes, as it has everything that I want in a cycling shoe. Now, I just need to get used to the stiffness of the shoe as I have not used a stiff road cycling shoe before, with my previous shoes all being MTB shoes that are more flexible.

Looks good on gravel and in the sunlight! 

Silver camouflage pattern blends in well with loose gravel.