advice please

hello i'm new to the site and already enjoying it!!!
Ive got a disco 2 td5 and my mates got a disco 1 300tdi, and we are both looking at buying a spare set of wheels for our disco and put All Terrains on them for green laning.

our disco's are totally standard and we need to know what size tyres to put on, or do we simply just put the same size AT tyres on as our road tyres.

Sorry for the daft question but new to AT's

many thanks

did you check the stickys at the top of this section

op2: :search:

didn't see the sticky at the top. cheers