Just an update for anyone coming to this thread for winter tire info - the directions on my Schwalbe Winter Marathon tires specifically state, "Tires need to be run-in for approx. 25 miles/40 km on hard-top road(my emphasis) to ensure spikes are permanently fixed." As lph above stated also, no rapid acceleration or hard braking during this period. It might seem counter-intuitive to ride on clear roads to break them in, but those are the directions. I'm about 15 miles into my break-in period, and it's just loud with more friction - no problems with handling or cornering, but I'm also going slower to avoid hard stops.