Originally Posted by CTC - the UK's national cyclists' organisation

To make it work with less cable you can effectively shorten the arm by anchoring the cable on the other side of the screw, so it's less far from the pivot. See the diagram. If B is made 69% of A, it should work perfectly. The dimensions are not too critical however. We’ve only got two indexing steps to make and shifters always provide a bit of over-travel, with exact positioning of outer and inner being taken care of by the stop screws. When you’ve checked that it works alright you can file a new groove for the cable.