Originally Posted by
Winfried
But do you really need an 818% range? Wouldn't a double chainring be good enough, wthout that issue with the tensioner?
A six-speeder + 50/34 chairing = 443%
And a Nexus 8 + 50/34 + 16T cog + = 452%
Hub Gear Calculator
Yes, I absolutely need the low gears. I even changed from 50/30+/24 to 50/34/20, in my memory, because I needed still lower gears. I might do with 22T as the smallest ring presumably though. I need the lowest gears for mountains and for winter. At times in winter I would ride exclusively on the 20T in front.
Originally Posted by
Jipe
Very interesting information, thanks for trying and sharing experience.
Could it work when changing the bottom bracket for one with external bearings and mounting the tensionner on this external bearing ?
Anyway, the bottom bracket box of the Birdy is different, made to let space to mount the tensionner besides an external bearing shell.
I think one could use a BB in Brompton with the lip of the BB cup filed down to a diameter that matches that of the shell + spacer(s) that also match the shell diameter + Dremel removal of brazing material. However, I found another product on AliExpress that goes under the lip of the BB cup, more akin to the Kamoya solution without the spring mechanism. It is on order and I will report on how it works.
However, overall, I think the problem has 3 levels:
A. Gathering moderate amount of extra slack for folded bike when one either puts the standard derailleur in the rear or adds a second ring in the front.
B. Gathering large amount of extra slack for folded bike when one puts either 3 rings in the front or a combination of 2 rings and a standard derailleur in the rear.
C. Gathering extra slack for a bicycle in riding, to eliminate tensioner or derailleur extended so that it rides close to the ground.
I think that A can be solved with some contraption along the lines of what is commercially available. I see no easy solutions for B. The most important for me is C, as I repeatedly drop the chain when riding the Brompton into a pile of snow when I am on the smallest ring in the front. Solving C would require an extra tensioner/idler with a wheel on the inner side of the chain, not outer. My interest in the potential solutions to A/B has been in their potential conversion for use in C. At present I see no solution for C, either.