I think that your C4 uses the same setup as our 308. I had problems with the lack of ground clearance and carrying capacity viewtopic.php?t=57919 and fitted some spring assisters from Grayston Engineering. I may be wrong but I think they may sell the actual springs for some cars. Might be worth contacting them? http://www.springassisters.co.uk/menu.htm
As I get older I think a lot about the hereafter - I go into a room and then wonder what I'm here after.
Inside every old person is a young person wondering what the hell happened.
"Trying is the first step towards failure" ~ Homer J Simpson