I really wonder that you did not recognize the difference, but maybe you are folding your bike another way than me.
The Strida can be folded in two ways, the drawings should explain that:
The drawings are showing the cross section of the three tubes, ~ 25 cms below the ball joint.
Possibility A:
The bottom tube is laying upon the steering tube.
Here is no difference in the belt tension noticeable.
Possibility B:
The bottom tube is clamped between steering and seat tube.
The belt is tensioned more than in unfolded position.
How comes that?
I’m sorry to say, but that’s not fully correct, actually is the freewheel fixed to the seat tube by the rear axle.
(The rear axle is screwed in the seat tube via a left-handed thread from the left side of the seat tube.)
The axle goes through the seat tube, at the right side the axle stump is linked to the bottom tube via the bolt 373 and (important) the cup spring 363.
There is some (not much) backlash between the axle stump and the bottom tube, the high spring force of the cup spring is pressing bottom and seat tube strongly together in unfolded position.
If the Strida is folded to fold type B the cup spring will be compressed and then the bottom tube can be moved sideways - I believe that is the only reason why Ming cycle had to use such a spring.
Would a usual washer be used at that position it would not be possible to fold the Strida to fold type B.
A nearer look makes it visible, actually the position of beltwheel and freewheel together have changed and the distance between the outer edges of the diameters has increased - the result is higher belt tension.
The drawings below are naturally disproportionated.
Please note that for the two pics below neither the cam (tripod) nor the bike frame was moved, only the bottom tube was moved from folding type A to B.
Bigger picture details:
Here the different angles of belt and tubes:
Dear Bietrume, I’m used from work that the engineers do not trust their workers, but I hoped that you know me better… 