Fnhon Ultegra Di2 12 Speed: Assembly Part 2

Here is the second part of this bike build, the Fnhon Ultegra Di2 12 speed drop bar folding bike. As explained in the earlier posts, there are a few problems that had to be solved for this build to be possible.

1) Custom Di2 battery mount.

2) Short derailleur cage for the Ultegra Di2 RD-R8150 rear derailleur.

3) Narrow wide chain ring that is compatible to Shimano 12 speed chain AND Shimano 4 arm road crankset.

Here is the completed build!

Ultegra Di2 shifters ST-R8170 with good ergonomics.

Fnhon Ultegra Di2 12 Speed: Assembly Part 1

With all the problems solved as described in the earlier posts, the assembly of the new Fnhon Ultegra Di2 12 speed can now begin! I usually wait until all the required parts are available before I start building, instead of building half way and then waiting for the rest of the parts.

First step is to install the new Ultegra R8100 11-34T cassette onto the wheelset. This is the same custom built wheelset by Ascent Bikes, and with the same Panaracer Minits Lite tires as used previously.

Ultegra R8100 11-34T 12 speed cassette installed!

Using the new XTR MT900 rotors, same as the ones which I am using on the Focus Paralane.

Fnhon Ultegra Di2 12 Speed: 12 Speed Cassette, Chain and Chain Ring

After solving the issue of the Di2 battery mount on the Fnhon frame, and modifying the Ultegra R8150 rear derailleur cage to a shorter version, I am almost ready to start assembling the bike.

The drivetrain and shifting components on the Fnhon Ultegra Di2 12 speed folding bike are mostly new, except for the Ultegra R8000 crank arms which will be carried over from the Dahon MuSP. I did not get a new Ultegra R8100 crankset to match the rest of the Ultegra R8100/R8150 groupset, as I only need the crank arms and not the chain rings. Therefore, it is more than good enough to reuse the R8000 crank arms on the new setup.

Let's start with the cassette. A 12 speed road cassette is needed for the Ultegra Di2 12 speed setup, and I can choose between a 11-30T cassette or a 11-34T cassette. On the Specialized Aethos and Focus Paralane, which have front double drivetrains and are dedicated road bikes, I chose the 11-30T cassette for its tighter gear spacing.

However, for this new Ultegra Di2 setup on the Fnhon, it will be a 1x12 speed front single setup. Therefore, the gear range will be decided by the range of the cassette, while the chain ring will shift this gear range higher or lower. I decided to use the wider range 11-34T cassette on the Fnhon Ultegra Di2 12 speed folding bike.

I actually had a Dura-Ace CS-R9200 11-34T 12 speed cassette as a spare, but decided not to use it on this bike. Instead, I decided to get a new Ultegra CS-R8100 11-34T 12 speed cassette, to match the rest of the components and also to do a comparison with the Dura-Ace cassette.

Dura-Ace vs Ultegra 11-34T 12 speed cassettes.

Fnhon Ultegra Di2 12 Speed: Short Cage Conversion using Ultegra RD-R8000

Although I managed to install the Mr TiParts super short derailleur cage onto the Ultegra Di2 RD-R8150 12 speed rear derailleur earlier, it was not a satisfactory modification. There were too many issues with the modifications that can affect the performance.

Therefore, I continued to look for a better solution to have a shorter cage rear derailleur on the Fnhon Ultegra Di2 12 speed folding bike. Then it occurred to me that I should consider original Shimano rear derailleur cages that are shorter, instead of third-party ones.

Drawing from previous experience when I modified the GRX rear derailleur with an extra long cage for the Cervelo Aspero gravel bike, it may be possible to find a compatible shorter cage to replace the stock cage on the Ultegra RD-R8150 rear derailleur.

After removing the Ultegra Di2 RD-R8050 11 speed rear derailleur from the Dahon MuSP, it was available for comparison. All R8000 and R8050 mentioned below are the short cage SS version.

Long outer plate of Ultegra R8150 vs the shorter outer plate on Ultegra R8050 11 speed rear derailleur.

Fnhon Ultegra Di2 12 Speed: Super Short Rear Derailleur Cage by Mr TiParts

While planning for the Ultegra Di2 12 speed setup on the Fnhon folding bike, there are a few issues which needed to be solved. One of them was to create a custom Di2 battery holder, so that I can hold the Di2 battery on the Fnhon frame.

The other issue comes from the smaller wheel size of the Fnhon folding bike. I will continue to use the custom built 451 wheelset from Ascent Bikes, as it is a disc brake wheelset and is still very useful. The problem is that the new Ultegra Di2 RD-R8150 12 speed rear derailleur has a pretty long cage, even more so than the previous Ultegra Di2 RD-R8050 11 speed rear derailleur.

Based on the Fnhon DB12 setup, it seems that the rear derailleur cage does not have much clearance with the rim or tire. Therefore, the new R8150 rear derailleur cage might be too long. It may still work in its stock condition, but there would not be much clearance.

Anyway, I decided to try changing the derailleur cage to a shorter version, to get more clearance. In any case, I don't need such a long derailleur cage as I will be running the drivetrain as a 1x12 speed drivetrain.

Mr TiParts makes third-party rear derailleur cages that are really short. I decided to give it a try and see whether it works or not.

The R7000 version was what I had previously for the United Trifold project, but didn't use it. It doesn't seem to be compatible to R8150 which is why I got a new set on the left, for R8000/R9100.