I bought a used bike whose chain keeps slipping, and I believe it is because either the chainring or the bottom bracket is bent. I tried to show this as best as I could in the below pictures.
I am looking to replace the chainring, but I can't for the life of me figure out what its real BCD is. It's a 5 bolt, and the adjacent bolt distance seems to be ~91mm, with a measured BCD of ~166mm. The below pictures show the taking of these measurements with a tape.
If I calculate the BCD from the adjacent bolt distance, it comes out very differently from what I am measuring it directly with the tape, and, even if it didn't, either of the numbers seem way off from whatever chainset BCD sizes I am able to find out there - unless this one is a very uncommon one? I mention that the bike is a 20 inch foldable Ecosmo mountain bike, 6 gear shimano. I haven't been able to find manufacturer info on it, but the chainring does have "9902-222-118-52T" inscribed on it, and the brand seems to be "Powerwheel". It has 52 teeth.
What am I doing wrong when measuring the BCD, and what chainring replacement sizes would be suitable for this bike?