They are 13cm - no idea what model I bought - I got them off ebay and threw away the box, but any 13cm speakers should fit provided they dont have a tweater protruding. If you go for components (like me) then youll not have this problem as the tweater is fitted seperately inside the car (I mounted them either side of the top engine cover).
By the way, the fronts are 13cm also - I bought some 2nd hand pioneer woofers for them, and used them in combination with the tweaters in the dash.
To be fair the std Renault fronts (made by Blaupunkt as I found when I removed them) arent that bad, but the Pioneers do give them a bit more oomph. The fronts are also dead easy to change - you simply pull the grill from the door panel, and again there are 4 torx screws. The fronts seem to be run off an existing x-over network, so if you do change the door speakers youll want to fit woofers without tweaters, else it wont sound right.
The terminals are different, so as Spammy says you have to crimp on some spade connectors to use with aftermarket speakers.
The result is a much improved sound, but ideally Id still like to add a sub on the shelf behind the seats, but so far Ive not found one compact enough (not that Ive looked very much), and it needs to be active also with speaker level inputs, as I cant be ar$ed to wire in a seperate amp!