Following are the rules according to the Swedish Transport Agency:
Winter tyres should be used from December 1st to March 31st. Studded tires are allowed between October 1st - April 15th unless it is / is feared to become winter road teams for another time.
Tyres for vehicles with trailers at winter roads:
It is important to know which tyre combinations for vehicles and trailers are allowed in winter road conditions.
For summer walls, tyres must have a minimum depth of 1.6 millimeters. In winter road conditions, at least 3 millimeters apply to light vehicles and passenger cars and at least 5 millimeters to heavy vehicles.