Why are snow tires used if all-season radials are supposed to be good all year?

For many drivers, all-season radials will be sufficient. However, if you live in the snow belt and do a large amount of winter driving you may want to consider snow tires. Snow tires have a more aggressive tread and are more flexible than all-season tires. This gives snow tires superior traction in the winter. Even though an all-season radial may have a "M+S" (mud and snow) designation, it is not truly a snow tire. A certified snow tire will have a snowflake-on-a-mountain icon on the tire's sidewall. This designation identifies that the tire met strict standards during American Society for Testing and Materials (ASTM) snow tests. ... more