I put on Blizzaks beginning
I put on Blizzaks beginning winter 2013. The tread was getting low last winter; so, left them on through the summer and they work fine. In fact Alberta EMS leaves them on year-round. I have a new set that will go on when snow's forecast.
The one thing to remember when changing over is that Blizzaks are directional. It can get exciting if the tires are mounted backwards.