A winter tyre with improved traction on snow surfaces; the tyre has a tread with a raised pattern defined by a number of longitudinal and transverse grooves which form at least one longitudinal row of blocks projecting radially from a base surface of the tread. Each block has two longitudinal lateral surfaces bounding two corresponding longitudinal grooves, and two transverse lateral surfaces bounding two corresponding transverse grooves. At least one of the blocks has lateral channels, each of which is formed on the lateral surface of a corresponding block, extends from the base surface of the tread to a top surface of the block, and is designed to impede radial spin-out of snow trapped inside the lateral channel.