What I found on the web (https://www.moto-collection.org/blog/3-roues-sur-langle/): "The articulated sidecar appeared in the mid-10s in Great Britain with Montgomery and, above all, in the United States with the “Flxible” which made Harley-Davidson famous on dirt tracks. The articulated sidecar sometimes even has a steering wheel allowing the side passenger to control the inclination. The device was very popular in grass-track racing and, on the track, Krauser in Germany was a distinguished specialist, before launching into the production of accessories... and the revolutionary Domani sidecar. Krauser raced on the articulated side for a long time before creating his own productions. On these articulated road racing sides, the deformable parallelogram (mounted upside down compared to the Jeanneret) includes a rack and a steering wheel which the passenger uses to control and force the inclination." I don't know who is right!
The Jalopy Journal
