OK, my bike is doing my f***ing head in.
It is frequently and unexpectedly scrunching & slipping when I pedal, causing the pedals to jerk forward and leaving me unstable, not even up hill or when exerting much load, i.e it happens on the level too.
The pedals and crank are secure, no wobble, and the bottom bracket was recently replaced (as it had come loose and damaged the threads). I had it in the LBS less than a month ago (when I got the BB replaced) and they said the chain & sprockets did not need replacing. Could it be issues with chain tension, the rear derailleurs?
Any ideas? I really can't cycle it anymore until this is fixed.