I used a 5 mm Dynema rope. The steel cable was too stiff and really hard to work with. I wrapped the rope on both sides of the bottom bracket and a single loop around the head tube.

There is almost zero play in the hinge now. However because there are two strands in parallel on both sides of the bottom bracket, when folding the bike the rope has to lengthen initially. Because of this each time I'm unfolding the rope loses some tension because I think the figure eight knot is settling.

So I have to tension the turnbuckle but I only got two centimeters left before I need to redo the knot to reduce the length of the rope.




I've also wrapped tape around the two strands near the bottom bracket and the head tube to keep the rope from slipping off from the slack when folded. The photos are from before I added the tape.