Jipe

There must be something wrong with the Crius implementation of the chainring tensionner because on the Birdy it works fine and the fold of the rear swing arm of the Birdy is the worst case because to fold the rear swing arm, the chain must be placed on the smallest cog which on a Riese & Müller Birdy Touring is 9t with a bigger cog of 32t, its 23t difference.

When looking at the Crius implementation, it seems that the chainring is very big, this could be the issue. The interference problem between the chainring and front wheel hinge attachment is a well known problem on the Brompton when a big chaniring is used.

On the Birdy, as said, the cassette is a 9-32t meaning that a 52t chainring is enough to have good gear inches. If a classic cassette with a smallest 11t cog is used, then a much bigger chainring is needed what can cause the problem ?

tcs

This Backer Gravity 10-speed seems to go the two chain guides + shift into largest cog route:


Gotta love the pseudo-Chp3 paint and cheeky Union Jack decal!

2_i 

Since I have been down this route, half of time the chain catcher will not catch the chain and, even after it catches, the chain can liberate itself during the transport of the folded bike. The video shows how one envisions this to work, not how it actually works in practice.

hihi2u2

Ok I've just ordered both chain tensioner at bottom bracket and rear mech. I'll see how that work, if it doesn't then I'll try the alternative Over Sized Pulley with the bottom bracket tensioner. I think the positioning of the bottom bracket tensioner is important. The example above is not tensioned enough it still looks very loose.

Jipe

The picture doesn't show how this tensionner works, if its like the one of the Birdy with an articulated parallelogram arm?

2_i 

The Birdy III tensioner for bottom bracket does not fit Brompton, however this Mr.TiParts hook may work.

hihi2u2

Thats the one on order, the shipping is delayed can't wait to start building !

2_i 

I have mine by now and it should work for single regular Brompton ring, with the Mr.TiParts' finger pointing at 3-5 o'clock.

My own situation is of 3 front rings, with the 3'rd ring very small and the issue is of taking out slack for chain on the smallest ring both in riding and for folded bike, with some stuff, chain stop, already mounted under the bottom bracket cup. There Mr.TiParts cannot easily help. I am exploring other paths, of different spring in the regular Brompton tensioner and wide idler mounted off the seat tube.

2_i 

I am not sure the particular tool on AliExpress, for widening the Brompton rear triangle got ever mentioned in BF. In any case, whether it is good or bad, it seems to fit this thread.

Schwinnsta

Why not just use a length of threaded rod with two nuts on the inside of the lockouts?

hihi2u2

Looked at it before, it doesn't expand to 130mm and this was confirmed with the seller. The bike has arrived now, waiting for the rest of the parts before sending it off for it to be widen. Cost £20 to widen £40 for the postage.

hihi2u2

Now the bike has arrived and I was waiting for the rear derailleur to arrive before sending it off.

In total I've bought two hangers and both don't fit. Any ideals from anyone?

One was aluminium (black) and the other titanium, both from aliexpress

2_i 

It is not clear whether the photos continue to show the situation with the same hanger or the other. In any case, it looks like the hanger in the first displayed photo would work. The fit is not ideal, but possibly good enough for the derailleur to work.

Myself, I tried two solutions. One was to get some random hanger off Ebay and using a router bit to shape it so that it would fit Brompton. Aluminum does not differ much from hard wood in machining, so a wood bit worked fine. Yes, my product worked fine on Brompton. Another solution was to get a hanger from brombacher.kr. In my memory, it fit well. However, the shipping price there doubled the cost.

As far as AliExpress is concerned, your experience is very common and the chances of any remedy from the AliExpress side are next to none. An AliExpress vendor wrote me that they ran out of stock for an item I bought, so I will not get it, as one recent example. It has been several months now and the best refund offer I got from AliExpress was for me to send the item back with a tracking number, with a refund issued once they receive the item from me!

hihi2u2

Yes I got the feeling the first one should work, if not then I just need to drill a hole in the second one (when I say drill a hole, it is titanium so it's going to be a challenge to do it at home).

Just an update, I've got all parts now and about to send the frame off to be expanded to 130mm. I was going to ask the steel bike builder to also install the bottom bracket for me. Before I send it off I thought I'd better check the TiParts chain tensioner, has anyone used this before?

Do you install it with the bottom bracket? If so, not all the tread would be engaged with the bottom bracket shelf ? Would it loosen over time because you can't get enough torque ?

Thanks,

Roland

2_i 

If you refer to the chain hook in the photo, yes I have it, but I could not make it fit Brompton. You cannot leave the bottom bracket cup hanging this much outside of the bottom bracket shell as in the photo - all kinds of bad stuff is going to happen, starting with the cup cracking.

hihi2u2

Don't worry it's not going to hang like this, it's a square tapered bottom bracket. Just to illustrate which part I think goes on first, i.e. the chain hook first then the bottom bracket cup. I can tighten it to the right torque but effectively it just becomes a spacer. Is this the issue you are having when you said it didn't fit yours ?

2_i 

I am trying to recall... The mount for the hook has a stiffening lip that forces you to orient the mount forward, as that lip interferes otherwise with the bridge to the rear triangle. However, for that orientation the mount interferes with the rear triangle after it gets flipped in the fold. In my case there are more factors, as I try to squeeze in more chainrings, but the above is there for any Brompton, I think.

hihi2u2

I think I know what you mean now (Turkish green is my bike), I might shorten the arm so it can be located similar to the black one. Will give that a try if all else fails.

2_i 

You might replace the extender arm with one made by yourself, just an alu strip with 2 holes.

hihi2u2

Finally finished building my bike.
In the end I've ended up using Ltwoo Folo B rear derailleur with jockey wheel and tensioner designed for Brompton. The fold works really well and the shifting is very smooth.

Ive widened the rear triangle with just nuts and bolts from hardware store in the end. No shops around me will take on the project, it was relatively simple to do. The more problematic and involving alot of trial and error was the spacing needed in the bottom bracket to make sure the 56T chainring clears the widened rear triangle.

I've started with my titanium square tapered bottom bracket, but there was too much horizontal movement. I've had to change to hollowtech chainset to introduce the spacing to make the folding work.

hihi2u2

Finally finished building my bike.
In the end I've ended up using Ltwoo Folo B rear derailleur with jockey wheel and tensioner designed for Brompton. The fold works really well and the shifting is very smooth.

Ive widened the rear triangle with just nuts and bolts from hardware store in the end. No shops around me will take on the project, it was relatively simple to do. The more problematic and involving alot of trial and error was the spacing needed in the bottom bracket to make sure the 56T chainring clears the widened rear triangle.

I've started with my titanium square tapered bottom bracket, but there was too much horizontal movement. I've had to change to hollowtech chainset to introduce the spacing to make the folding work.

Jipe

Very nice bike !

This derailleur seems to be the solution to have a real derailleur+cassette on a Brompton and a good chain tensionning when folding the bike without any additional chain tensionner ?

2_i 

Congratulations on getting there and this on your own. I wonder about the situation with the chain on the lowest cog. How far is the tensioner arm then from the ground? Can you fold then fine without the chain getting loose or do you need to watch on which cog you need to fold? With the bottom bracket, was that that the chainline was off? Did you try asymmetric placement of the bracket, different amounts of sticking out to the left than right? What is the cassette you ended up using? Thanks.

Jipe

Same questions, I couldn't find this derailleur on the website of L-Twoo, (its also not the website in Chinese).

hihi2u2

Yes no additional chain tensioner needed and tensions perfectly