With more time to optimize my 2-ring Brompton, I evolved the setup towards that of Winfried in
https://www.bikeforums.net/folding-b...eur-clamp.html
Specifically, I switched to the
Litepro Braze-On Adapter Clamp for Dahon K Frame. There is another one for 1/4 of the price,
SP8 40mm Derailleur Adapter, that seems functionally equivalent, but it is still in the mail. I combined the clamp with Shimano Tiagra FD, following Winfried, and Sunrace M96 Thumb Shifter.
The problem in adapting clamp-on derailleurs to Brompton is in the fact that Brompton's seat tube does not point towards the BB axle yielding a mismatch between the angle of FD cage and chainring circumferences. The clamps above have fingers for mounting the FDs that solve that. In addition those clamps have 3 places where derailleur angles and elevation are adjusted, allowing to fine tune the derailleur placement far better than typical for clamp-on derailleurs on standard bikes. The end result is that it is far easier to get a good shifting. It was fine with my earlier setup but the range within which all worked fine was more narrow, The Litepro clamp was a tad too large for Brompton seatpost and I glued some tube rubber to its inside to make it fit, which was presumably a good idea anyway. There is an expected flex in the finger of Litepro holding the derailleur when shifter cable is pulled, but the finger then leans against the seatpost, so it is seemingly OK.
Regarding the shifter, I decided that I wanted to regain grip space. I actually like ergo/contour grips.
Finally, I shortened the BB, going to 113mm with titanium axle, shifted towards nondrive side. The latter is because I continue to use the original Brompton left side crank. If I swapped both cranks and go with symmetric BB, presumably 109mm would be optimal. However, the BB swapping is optional. You can live with the original Brompton BB.
My current weight change is:
- 486-414=72g (RH crankset)
- 54g (der mount)
- 87g (der)
- 10g (shifter cable)
- 45g (cable housing)
- 76g (shifter)
- 159-237=-78g (BB)
for the total of 266g (344g w/o BB swap). I think this project is now complete. The photos illustrate the final result.