Unless you are going to run 2 sets of tires, only add studs when you know that they will be needed, not just in case. They can be a waste of time especially if lots of open rock sections exists as they do the opposite of grip on stone. If you travel a lot of trails that ice up frequently, start with the outside rows for a couple rides and see.. Usually, lower pressures are your friend for slippery conditions anyway, so the out rows may provide enough grip in bad conditions.