jmtalire

Hi im new to this forum and im by no means a car expert, so please excuse any ignorance :) I recently aquired my first diesel car; a Citroen C4 1.6 VTR +HDI (no idea what all the letters mean, but i know its quite nippy). Now, going from a life long petrol car driver to a diesel, im finding when to change gear and a what rev's to be quite tricky (may sound silly i know). In my petrol a drove 30mph in 4th, and 40mph+ in 5th; easy. But now in my diesel im finding driving 30mph in 4th and 40mph in 5th to be too low a gear. Could any fellow Citroen or diesel drivers please advise if im driving it correctly? And also at what revs should i be changing up gears and driving at a constant rev should i be using to drive economically? Thanks in advance for any advice given :D