Winter traction consists of the following three components:
The rubber compound used in a tire can be fine-tuned for particular characteristics. A summer compound is designed to be very sticky and offer lots of traction in warmer temperatures. As temperatures drop, the compound firms up and in effect it freezes. The compound loses its stickiness as it hardens, resulting in drastically reduced capabilities in winter environments. An all-season compound tries to be a jack-of-all-trades and has a compound that is more receptive to colder temperatures. However, a dedicated winter / snow tire has a compound that stays soft and pliable in cold temperatures that results in higher levels of grip during the winter months.
Snow on snow traction is critical to winter capability. This is achieved by packing snow into the depths of the tread upon contact with the surface, and then releasing as rotation continues. Winter / snow tires will feature 11/32" - 12/32" of depth when new, while most all-seasons start at 10/32". While U.S. law stipulates 2/32" of tread depth renders a tire legally worn out, winter traction requires a bit more to be effective. Once you reach approximately 6/32" of remaining tread depth, you've lost this element. To gain a better understanding of why winter / snow tires should be replaced when they reach this level, read "Tread Depth - Why Too Little is Never Enough."
One of the key features in a winter tread design is sipes. Sipes are small slots or cuts in the tread design that create biting edges, allowing the tread to "cut through" the ice and snow and conform to the road surface. These sipes start to disappear around the 5/32" tread depth mark and will affect the stability in the contact patch. If the sipes were cut down past this point, the tire could have a loose and squirmy feel to it.
When you're ready to begin your winter / snow tire search, take a look at our wide selection of options by brand.