In order to have a separate gravel wheelset that can be swapped quickly with the standard road wheelset, it is necessary to have an additional cassette and disc brake rotors on the gravel wheelset as well. This way, the wheelset can be swapped in without adjusting or changing any other component.
In this case, a new cassette is needed on the gravel wheelset. If I were building a gravel bike from scratch, with a new frame, most likely I will go for a front single drivetrain, with a wide ratio cassette at the back. For example, a 40T chain ring with a 11-42T cassette at the back.
However, since I am modifying the Canyon Endurace to be a part-time gravel bike, I need to maintain the front double drivetrain that is needed for road riding. Just to recap, the Canyon Endurace is equipped with a full Dura-Ace R9170 groupset, with the 50/34T crankset and a 11-30T 11 speed cassette.
A front double crankset is actually pretty good for a gravel setup as well, as the small 34T inner chain ring can provide a low gear ratio for off-road riding. Usually, a gravel setup will have a lowest gear ratio of 1:1, to enable grinding up steeper slopes. In this case, since the small chain ring is already 34T, a 11-34T cassette will achieve a lowest gear ratio of 1:1, or roughly 28 gear inches with 700C wheels.
A larger 11 speed cassette would be 11-36T or even 11-40T, but it is probably not necessary with the low 34T chain ring available. Besides, the gear sprocket difference between the gravel wheelset (11-34T) and road wheelset (11-30T) should be minimized for better shifting performance, as will be explained later on.
Ultegra grade CS-HG800-11 cassette, 11-34T 11 speed.
The compatibility graphic on the packaging is a bit confusing, because this 11 speed HG800 cassette can actually be used on 8/9/10 speed freehub bodies, just by omitting the 1.85 mm spacer that comes with the cassette. A 11 speed MTB freehub is the same as a 8/9/10 speed freehub.
Ultegra grade finishing on the sprockets, but it is not classified under Ultegra R8000. Probably because the cassette structure is a bit different, as it can be used on 8/9/10 speed freehub bodies as well, not exclusively on 11 speed road freehub bodies.
Weighs 337 grams, including the 1.85 mm spacer. 130 grams heavier than the 11-30T Dura-Ace cassette.
Gear sprockets are 11-13-15-17-19-21-23-25-27-30-34.
I don't like the large 11T to 13T jump at the top end of the cassette, as explained before here. That is the case if all the gears are used, such as on a 1x11 speed drivetrain where the full gear range is utilized.
However, I realized that on this 2x11 speed Di2 drivetrain, the cross-chaining is electronically limited. Basically, if you are in the small 34T chainring, the rear derailleur does not allow you to shift to the top two gears on the cassette (11T and 13T in this case). The reason is to prevent chain touching on the large chain ring due to the cross chain angle, and also to ensure that the chain capacity of the rear derailleur is not exceeded.
In other words, when I am using the small 34T chainring, I am limited to 9 gears at the back (15T - 34T). The top 2 gears on the cassette are only accessible when in the large chain ring, where it is hardly used as the gear ratio is usually too high for me. In conclusion, the large jump between 11T and 13T does not come into play at all, as it is not selectable (when in small chainring) or the gear ratio is too high (when in large chainring).
The 11 speed 11-34T cassette disassembled.
Rear view of the cassette with the large aluminium spider. Note that the largest sprocket is cantilevered out over the spider, beyond the freehub body. This is what enables it to be mounted on older 8/9/10 speed freehubs.
The largest 3 sprockets (27T, 30T, 34T) are mounted on an aluminium spider, and is specific to this cassette.
Next 3 sprockets (21T, 23T, 25T) are also mounted on an aluminium spider. This is different from other Ultegra cassettes which use carbon fibre for the second spider.
This second spider is also specific to this cassette only.
It has an aluminium lock ring, but then uses resin spacers instead of aluminium spacers of other Ultegra cassettes.
An additional 1.85 mm spacer is provided, which should be used ONLY if you are mounting this spacer on 11 speed freehub bodies.
If done correctly, the top 11T sprocket should protrude from the freehub body thread by a couple of millimetres.
If you miss out the 1.85 mm spacer when mounting on an 11 speed freehub body, the whole cassette will sit too far inwards, and the lockring cannot secure the casette properly. This picture shows the wrong setup.
In my opinion, branding the cassette as a non-series HG800 is correct, as it is a bit short of the Ultegra grade quality expected. Besides using resin spacers instead of aluminium spacers, the second spider does not utilize carbon fibre material, which is another difference.
With the cassette settled, let's move on to the rear derailleur. The Canyon Endurace is currently using the Dura-Ace R9150 Di2 rear derailleur, which is rated for up to 30T large sprocket and a maximum chain capacity of 33T. If I use the 11-34T gravel cassette, the total chain capacity required would be (50-34) + (34-11) = 39T.
If we discount the top 2 sprockets (11T and 13T) as it is limited by the Di2 system, the chain capacity required would be (50-34) + (34-15) = 35T.
In this case, the R9150 rear derailleur cannot achieve both the required max sprocket size and also the chain capacity. Therefore, a new rear derailleur is needed to match with the larger 11-34T sprocket.
Remember, my objective is to enable the road bike to be transformed into a gravel bike, just by a change of wheelset. The rear derailleur and chain must be compatible to both the road and gravel setup, without any adjustment required during the swap. My plan is to set up the rear derailleur and chain length to match the larger 11-34T gravel cassette, and this same rear derailleur and chain setup also needs to work for the 11-30T road cassette.
The Ultegra RD-R8050-GS (mid cage) Di2 rear derailleur is compatible with a 34T large sprocket, but if I'm going to make a gravel setup, I might as well use components from the new GRX gravel groupset. There are a few new GRX rear derailleurs, to suit different gravel setups (1x or 2x, mechanical or Di2 shifting). What I need in this case is the GRX Di2 rear derailleur for a 2x11 speed drivetrain.
Nice packaging graphic to signify the GRX gravel component.
4 types of GRX rear derailleurs available. I would be using the RD-RX815 which is the Di2 rear derailleur for a 2x11 speed drivetrain.
GRX RD-RX815 Di2 rear derailleur. Shadow construction, similar to RD-R8050, but with an aggressive outer link design. The design language is in-between road and MTB, which works well for gravel.
The aluminium cage is quite long, to achieve a max chain capacity of 38T. This is helped by the large 13T tension pulley at the bottom. Otherwise, the structure is similar to the RD-R8050 used on the Dahon MuSP.
Most importantly, this GRX rear derailleur is equipped with a clutch! This increases chain tension to minimize chain slapping and eliminate dropped chains. Already in use on MTB rear derailleurs for many years. This will be super useful for gravel riding.
Weighs 287 grams, which is 90 grams heavier than the Dura-Ace rear derailleur. This is expected as the GRX rear derailleur has an additional clutch, a longer cage, and does not use carbon fibre outer and inner plates.
Comparing the GRX rear derailleur with the Dura-Ace rear derailleur which is still on the Canyon Endurace.
Comparing them side by side. Similar Shadow construction, but the GRX rear derailleur seems to be the more capable one, with a larger chain capacity and a clutch function.
In order for this road/gravel setup to work, this new GRX rear derailleur needs to match both the 11-34T cassette on the gravel wheelset, and also the 11-30T cassette on the road wheelset. I will basically have to set up the rear derailleur B tension screw using the 34T sprocket, and hope that it will still shift well on the 30T sprocket on the road wheelset.
The chain length obviously has to be long enough to suit the 34T cassette, so a few links need to be added onto the existing chain. The extra chain length (+6 links) will not be an issue as the longer cage can take care of that.
Areas to take note is the indexing of the rear derailleur on the cassette, as each cassette's position might differ slightly. If they are close enough, shifting performance should be good enough across the two different cassettes and wheelsets.
With the 11-34T HG800 cassette and GRX rear derailleur installed on the Canyon Endurace.
Using the GRX rear derailleur means that the Dura-Ace groupset is incomplete, as the Dura-Ace rear derailleur is no longer used. For me, this is OK as I am no longer obsessed with the weight of the Canyon Endurace any more, unlike previously when it was new. Besides, using the gravel wheelset and tires already add much more weight than the little difference a change of rear derailleur makes.
Testing the gravel setup!