You can spot a winter tyre because it features a ‘Snowflake on a Mountain’ symbol on its side wall, indicating that it satisfies the safety criteria for winter conditions.
Another difference between winter tyres and summer tyres is that winter tyres should be replaced when their tread reaches a depth of 4mm whereas 3mm is the recommended minimum depth for summer tyres. As you will see from this diagram, stopping distance increase as tread depths decrease. So a new tyre, with 8mm tread, will stop faster than one with 4mm and considerably faster than one with only 1.6mm remaining. In fact, once the tread has worn down below 4mm, the benefits of the winter tyre have little or no effect on snow or ice.