Well, whatever I was doing I just gave up. I googled it and some people get these chain loops accidentally when servicing their bikes and those don't really seem easy to fix unless you have a chain tool, which I don't.
No more biking for me until 2015 when I return. Then I'll take it to the repair shop, I'm sure the guy will fix it quickly and inexpensively (I hope).
I will also take the occasion to test the ISPs, because 1) I couldn't even ride the bike with them now and 2) the temperatures are not so harsh right now that I could find ice, but I'm sure that in January a different tune will play.
Btw. When changing the tires I noticed this blue band on the rims.
Are my rims already ghetto-converted to be tubeless-ready?
edit: just googled it as well and it's just an inner tube protection. Gosh, you can really tell that I just got into this hobby this year