Thanks for your replies.
@bargainguy
Thank you
I know about Tern's issues, but it seems they've somehow manage to make it right, or am I misinformed?
Good idea about a smaller chainring, might help!
@Joe Remi
Thanks for letting me know, it really might be just this bike.
@tmesis
Almost forgot about Tyrell Ive. This seems like a really nice option for me. Problem is it's not sold here in Slovakia/Czech Rep. Maybe I'll try it in person when I'm in Berlin. Really like the design and the fold also seems simple enough and compact.
@Odontites
Thanks for info, good to hear that it might be just my friend's bike.
@berlinonaut
Idk, I probably need to pump them again. They are actually Schwalbe Marathon tires – so slower then Brompton's Kevelar, but shouldn't be THAT noticeable, right?