Mystery resistance?

BTW in retrospect i've just realised that this has started since I've learnt to skid i.e. been exerting really high forces in various directions on the chainring, thus bending it.
Interesting. my BB problems have started since learning to skid. The BB seems a bit loose, and the axel wobbles. It makes a knocking, grinding noise intermittently. Chainring is really worn as well, so I can't be too bothered to get it all fixed, as I'm building up a new bike.