Composition of a winter tire.
A quick lesson, in case you fell asleep in class: mechanical attributes (the tread pattern) and molecular construction (the rubber compound) are the two features that separate a winter tire from an all-season hoop.
The first is easy to visually see. It’ll not escape your notice that tread blocks on a winter tire are packed with little zig-zag cut features. These are called sipes. They open up slightly when pressed into the road surface, creating extra biting surfaces to provide more grip (the Continental VikingContact 7). A close examination of those tread blocks will also reveal edges shaped like a serrated blade, another design decision intended to create extra grip, not unlike when a cat’s claws dig into the sofa (the Yokohama iceGUARD iG53 tire).
Those who claim all-season tires perform similar to winter tires may try to argue there is little difference in how the two are constructed. In defense, try this experiment. Take a block of normal styrofoam and push it along the surface of your kitchen table. It slid pretty smoothly, right? Now, cut four or five shallow grooves in the styrofoam’s surface and try to push it along the table again.
Different, eh? The extra surfaces you made when cutting grooves in the styrofoam create more area for grip. In the tire industry, these grooves are called sipes. The tread blocks of a winter tire are designed to cut through snow and slush, evacuating the liquid that can get in between the rubber tread and road surface. Using sipes, they create extra contact patch and gripping areas which provide control when accelerating, braking, and turning.
Visually seeing the rubber compound in a winter tire isn’t possible, nor is finding out specifically what the compounds are comprised of. Tire companies play their cards close to their chest, guarding their recipes closer than Colonel Sanders guarded the 11 herbs and spices. Still, if one were to press on a winter tire in the way one would test the freshness of a melon at the supermarket, they’d find it to be much more pliable than a high-performance summer tire.
Molecularly, a winter tire is made up of different rubber compounds than an all-season tire, allowing it to remain a bit malleable when the ambient temperature drops. Without this flexibility, a tire will simply skate over the ice and snow rather than grip it.