Here are the original specs for the bike:
40T chainring, 2-piece (yes, 2 piece) crank
15T cog
Sachs Torpedo single speed, coaster brake hub with 110mm OLD
narrow fork spacing around 95mm (same as vintage Raleigh?)
20x1.75" Vredenstein whitewall tires
steel wheels
Weinmann sidepull brake in front
The German wikipedia page on folding bikes (klapprad or faltrad in German) shows a bike similar to mine:
An old issue of the MIT student newspaper from the 1970s shows an advertisement for my bicycle.
Mark Rehder's website on the Austrian
Auto-Mini.