It looks like you’ve done your homework on your build and you’ve mentioned concerns about the stiffness of possible carbon components in your OP but you haven’t commented on the mainframe stiffness. Note the following comment.
Originally Posted by
ch99_lee
Very nice clone you got there. I built a similar one a years ago with all titanium frame with 12 speed force AXS derailleur. Weight around 6.64kg. But it is quite flimsy to ride.
The above was the only reference I could find today but I know others have commented on the flexibility of the ride of titanium Brompton clones in this forum suggesting they are not as stiff as a steel framed Brompton. Compare images of the T-Line Brompton main frame tube with those for the Aliexpress titanium clones – It looks a lot larger diameter.
I’ve been down the “build a better Brompton” road using Columbus SL tubing where possible. I was happy with my first attempt (20” wheels, 21 speed SRAM Dual drive, asymetric main frame tubes to allow very compact fold, increased BB height, Vee brakes, Thudbuster seatpost instead of rear triangle bumper for suspension) but it was heavier than I wanted at about 12 Kg.
I tried everything I could think of to reduce frame weight for my second attempt including using smaller diameter main frame tubes, but I had to back track on that idea because the frame flexed too much when I tried it.
The final version is here:
Is there a Brompton style frame for 20 inch (406) wheels?
In short, I suggest you concentrate very strongly on every possible aspect of stiffness otherwise you may end up with a superlight build which rides like it’s a basket of sticks.
By the way, why did you choose Grade 5 titanium? I’ve just looked at 6 different manufacturers who all quote Grade 9 for their frames. Only Bossi in Australia (frames made in China) quote Gr5 castings for head tube, BB and seat/toptube intersection – maintubes are still Gr 9.