My chain needs replacing and after checking the tips of my sprockets for flatness (thanks donkey for that advice) I realise I need new sprockets as well. I'm wondering about changing the ratio. The rear is 47 teeth at the moment. But I'm wondering what exactly are the effects of changing the ratio? Like what does more teeth and less teeth do? I know its related to top speed and acceleration but can't remember which does which. Any help/general advice?