Yesterday while rolling quickly down long empty hills I experimented with taking my hands off the steering. As others have reported, when this is done the front wheel of the Birdy instantly starts to shimmy very badly.
The movement doesn't build up - it just immediately happens. It's weird because when being controlled by two hands, the bike's front end feels immensely stable. Even with one hand off the steering, at speed the stability feels marginal.
Has anyone ever fitted a steering damper to a folding bike?
I have seen them available for normal bikes, and many motorcycles use them.