As the name suggests, both winter and summer tires are specifically designed for that particular season. Before we delve deeper as to why that is, it is pertinent to understand what exactly separates these tires, and how these differences can impact their performances. There are three fundamental differences between summer and winter tires: their structure, rubber compound, and tread pattern. And not all of these differences are visible.
Some countries insist that tires be swapped from summer to winter as the cold weather approaches. But what are winter tires? And why are they compulsory in some places but not others? In cold weather, the regular all-season tires’ rubber and the rubber used in high performance summer tires hardens at a higher temperature than the rubber compound used winter tires. This is problematic since the rubber must retain flexibility to grip the roads. At about 42 degrees Fahrenheit, an all-season and a winter tire have about the same traction; however, as the mercury drops the winter tire gains grip, while all-season tires and high performance tires lose traction. Moreover, at temperatures well above 42 degrees Fahrenheit, the rubber in all-season tires stays hard and resists wear and tear. In contrast, the rubber in the tread of a winter tire will soften, and wears out much faster. For this reason, winter tires should be removed from the vehicle early in the spring and replaced in late fall when the temperatures regularly dip below 42F.
Furthermore, winter tires have higher natural rubber content – containing a larger percentage of natural rubber and silica in the compound – keeping them agile in the cold. The softer they are, the more the tire is able to interlock with the road surface, improving grip and handling. Winter tires also have thousands of tiny grooves in their tread blocks which are used to disperse water and prevent aquaplaning thus providing optimal grip on the road. Their tiny grooves bite into snow, ice and sludge, dispersing water at a fast rate and ensuring better breaking and more traction. As far as the tread pattern goes, the winter tires have cavities for snow which allows a better grip in the snow, adding traction adding traction to push the vehicle forwards on icy roads.
Summer tires, on the other hand, have a relatively hard compound which softens in milder temperatures to be able to adapt to dry as well as wet roads. They also have fewer grooves than winter tires, but have specially designed tread bars to minimize aquaplaning. These provide better grip, both longitudinally and laterally in warm temperatures, ensuring lots of grip on wet and dry roads. They also have a harder rubber compound with less natural rubber than winter tires and this begins to harden and can become brittle below +7 degrees C. That said they are designed to adapt to higher temperatures without getting soft. This means that summer tires have lower friction and therefore are more fuel efficient.
Hence, winter tires are meant for the cold with deep treads for greater grip. The tread rubber on winter tires is softer than regular tires and wears out faster on warm pavement, leading to more frequent replacement. Softer rubber on dry pavement results in less precise handling and responsiveness giving your car diminished performance. All of the above necessitates changing the tires according to the weather conditions of the particular country as they can affect the performance and safety of the car.