Tires: winter tire vs A/T tire, all terrain tires, ranked winter

Question
hi barry !
my name is jason i have a 2006 MB ML350 with 235/65r/17 all-season tire it's about 70000km i am thinking about get new tire ! i travel by this car a lot and winter is coming i live in canada, i just wanna know what is the difference between winter tire and on/off-road A/T tire ? cox from tirerack online survey ( http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=ORAT )it seem the top 5 ranked A/T tires works very well in winter and on snow and ice . and they also have the offroad ability even at summer time and cheaper too compare to some top ranked winter tire ! can you please tell me what is the best choice for me ? and do the A/T tire working as good as the winter tires ?
thank you very much !!!

Answer
Jason,

First, I can't tell you what will work best for you as this is highly dependent on the weather conditions and the road conditions where you live.  You need to consult with folks in your area to determine what is best for your locale.

When people do an on-line survey, they are looking at not only how the tire performed, but also how it performed compared to their expectations.  If they expected "Middle of the road" snow performance, they would give high ratings to any tire that gave them "Good" performance.

But to answer your question:  Winter tires are designed exactly as advertised - to give good winter performance.  That means good snow traction and the ability to work when temperature is cold.  Needless to say, these tires are unsuitable for year round usage.

All Terrain tires are designed to be used only slightly "off road", but the amount of "off road" compatibility varies considerably from tire to tire.  Many of the design features of All Terrain tires are also design features for winter tires.  However, All Terrain tires are not going to work as well as winter tires in those conditions where winter tires are designed to operate.  By the same thought process, winter tires aren't designed for off road usage.

I have heard from many sources that if you live in Canada, winter tires are a "must", but I have no way to verify this.