United Trifold: Rear Hanger and Rear Derailleur

From the previous modifications, the United Trifold has been set up as a lightweight single speed folding bike, with a weight of just 9.3 kg with pedals. That is a huge difference from the stock weight of 12.6 kg with pedals.

I am pretty happy with a single speed setup, as this bike is only used for casual rides. However, I was asked if it was possible to change the bike to a multi-speed derailleur setup. At first thought my answer was no, as there are just too many limitations.

Due to the trifold nature, the chain management becomes very tricky when folding the bike. Also, the limited space around the rear triangle area always causes interference, and solving one issue is likely to cause another issue. All these experience is from my previous modification of the Brompton M6R.

However, the United Trifold does have a few differences that gives it a bit more chance of a successful derailleur drivetrain conversion. For a start, the rear OLD is a standard 135 mm, which means that a standard wheelset with standard freehub body can be used. This already solves the biggest problem that a Brompton has.

Also, since my United Trifold is already using a standard 11 speed freehub body, it is not too difficult to put on a cassette and try out the idea of a derailleur drivetrain.

Therefore, to answer the question of whether a derailleur drivetrain conversion is possible, I decided to use my bike to experiment. It may not be successful, and I don't really need a multi-speed drivetrain, but it would be fun to try anyway.

I did some research and asked Brompton experts on how to modify a trifold bike to use a derailleur drivetrain, and got some very useful advice.

Example of a derailleur drivetrain on a trifold frameset.

One of the major hurdle that must be overcome is to get a rear derailleur hanger for the United Trifold. I was lucky to be introduced to this hanger as shown below.

Available in Brompton design or 3Sixty/Other design. I think the difference is an extra protrusion on the Brompton type to fit into the Brompton frame.

From what I see, the slot will match the rear dropout, while there is a hole at the top to secure the hanger to the frame.

Let's see if the cutout shown here fits the frame! No idea if it would work, as the United Trifold is a pretty unique bike.

Stock set weighs 22 grams. However, not all the parts will be used.

Here is how the dropout of the United Trifold looks like.

I was surprised to find that the hanger fits perfectly! The hole is even in the right place to secure the hanger to the frame.

With a M5 bolt threaded into the frame, the hanger is secured, together with the cutout at the back to rest against the frame. This is a good start!

Once the quick release axle is added, the hanger would be fully secure.

On hand, I had a mid cage (GS spec) 105 R7000 rear derailleur to experiment with. The last mechanical rear derailleur I used was a long time ago, the previous generation Ultegra 6800.

Being a mid cage rear derailleur, the cage may be too long for a 16 inch 349 wheel bike. It does have an advantage of having a larger chain capacity for chain management.

The rear derailleur cage is nearly as long as the Litepro chain tensioner. 

Weighs 226 grams, just for the record.

Found that there is interference between the rear derailleur adapter and the dropout, due to the protrusion on the adapter.

Due to this interference, the rear derailleur cannot be properly fixed onto the adapter.

Here's the reason, the TiParts rear hanger (in black) has more material than a standard hanger.

Based on this comparison, I made a marking to indicate where to remove material.

The area highlighted in blue needs to be grinded away from the hanger.

After grinding away the interfering material, the rear derailleur now fits on the hanger nicely!

No more interference

Here is the first step of this experiment, to see if the United Trifold can be converted to use a derailleur drivetrain. For a start, the hanger and rear derailleur seems to fit on the bike, so we can move on to try other components.