18s on a clio are defo possible as i have them as well, mine is lowered 40mm and it is tight as a badgers arse but i looks wicked, the bodykit i got needed altering slightly to fit the wheels i can have a full car and full lock no probs, only thing i will say is this is scrubs slightly on the drivers side rear but thats due to the side skirt being in the way. I asked merseyspeed about a 60mm drop it will need work but it can be done.