... as Gary said ...

http://www.tirerack.com/winter/tech/techpage.jsp?techid=151

the fact that these would be retractable is good, but how many drivers would remember to do it? ...

how about this:

https://www.google.com/#q=tire+chains&tbm=shop

I remember driving with tire chains ... a link would break and the chain would get all tangled around the wheel ... trying to free it up in freezing cold weather ... what a PITA !!! ...