Studded anytime it is winter, or snow on the ground. Learned my lesson the hard way. Did a full on left body slam against the pavement in the rain. Literally the only pile of snow on the commute, a shadowy corner with some frozen melt unseen with the rain. Knocked the wind out of me with my left arm tucked under me and yes, the helmet worked well. 10 minutes later I shook it off and got my breathing and nerves back. And pedaled the last 8 miles to work. HTFU.