I could take a look at the rear mech on my commuter (f*ck it, I could throw it away and stick on another- I got it for a penny, excl P&P). The thing gets stuck about halfway down the block and won't make it to the little sprockets. Except I've found I can set the downtube lever about where I want it and aim for a pothole. Usually does it. Need a bigger pothole for a bigger change. Haven't got it into top yet- probably need a speedhump for that.