After experimenting with a few different derailleur setups on the United Trifold earlier, I decided to switch back to an 11 speed road setup. This time, I will use a short cage (SS) 105 R7000 rear derailleur, instead of the mid cage version earlier. By doing so, this would solve the ground clearance issue.
Short cage 105 R7000 rear derailleur on the left, mid cage version on the right.
Looks similar from this viewing angle
There is some difference at this area, where the cage is attached to the body of the rear derailleur. This is due to the different large sprocket compatibility between the SS (max 30T) and GS (max 34T) version.
Comparing the mid and short cage derailleurs side by side.
Mid cage length is about 87 mm
Short cage length is about 72 mm
Mid cage weight is 226 grams
Short cage weight is a bit lighter at 220 grams.
Just changing to the short cage R7000 rear derailleur will not solve the slack chain issue, as previously experienced on the mid cage setup. Other chain guides that are used on Bromptons will not fit this United Trifold due to the frame or crankset interference.
Therefore, I got this chain tensioner that was commonly found on older Birdy bikes, before the bottom bracket-based chain guide was invented.
Small extension which will be attached to the rear derailleur cage, to manage the chain when the bike is folded.
This small chain tensioner weighs just 16 grams
At the top gear (smallest sprocket), adjust the chain tensioner so that it just clears the chain.
Adjust the chain tensioner angle so that it avoids the chain.
Plenty of ground clearance, with the cage at its lowest point.
As the chain is shifted inwards to the larger gears, the cage rotates upwards, together with the chain tensioner.
No issue with ground or tire clearance, with the short cage rear derailleur.
Chain at the lowest gear (largest sprocket). Chain length is barely enough, as shown by the super-stretched cage position.
Barely any chain engagement with the top guide pulley. Still able to shift though.
With this additional chain tensioner on the short cage R7000 rear derailleur, I am able to find a balance between good ground/tire clearance, and also sufficient chain management.
In the next post, I will summarize this derailleur drivetrain modification of the United Trifold.
have you tried to fit GS rd with SS cage?
ReplyDeleteThat would be possible, although it is easier to just change the whole RD. Not just the cage length is different, the linkage design is different as well. https://handsonbike.blogspot.com/2017/12/dahon-muex-1x11-drivetrain-ultegra-di2.html
DeleteHi Steve
ReplyDeleteWould u know for early 2000 dahon, presto aka helios, rear derailleur hanger ..are they universal or how to pick 1 for mounting as I am converting single ?
And for folding bikes, will GS RD able.to clear ground clearance? As most MTB groupset are with GS ..