summer tires, all season tires, snow tires, etc etc. are all rated from the factory. summer / winter tires are built specifically for their purpose and outperform a generic all season tire when used in the right conditions.
for example, summer tires are usually far better in moderate to warm temperatures in dry and wet weather than any all season could ever hope to be. however, they are unuseable in the cold temperatures of winter or in snow. so, if you have summer tires anywhere that has seasons, you'll need to switch them out for the winter. i have summer tires and snow tires
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bryan