Yeah, the most concise indication for the need for studded tires, is your bike and body slapping the pavement due to a tire slipping on the ice. By that time it could be a bit late to make the decision to purchase. I run studs anytime there is ice around, whether that means that it snowed a week ago or today. Snow melts and turns to ice around here and I am not fond of smacking frozen pavement with my body.