Well time has come for me to replace my chain and sprockets, but wondering what size socket i need to take off the rear sprocket as its quite a big bugger!!

Cheers Guys!

if you mean that super big ass one you would need a breaker bar for, then dont worry, that stays on. there are 6 14mm(i think) bolts holding it on. just unscrew that and off they come. then again, thats if you are talking about a NC30 or 35.
you never mentioned.

welcome to the site

i presume you are maybe thinking of the hub nut which is 46mm.........the nuts that hold the sprocket on to the sprocket carrier are not relatively big,14mm at the most but i think they are either 10mm 0r 12mm......
the rear sprocket is held on by six nuts and the hub nut does not need to be touched to remove the rear sprocket....just the six nuts. :D :D

Mine are 12mm nuts on 8mm studs but I do have Ti Studs and Nuts so I'd guess it's either 12mm or 13mm.