A stud unit (3) and a device (1) for a studded tyre. The stud unit comprises a housing (5) with a chamber (7) enclosing a medium, a stud (20) arranged at least partly inserted into the chamber so that it is affected by the medium. The stud is adapted to be moved depending on a change of the pressure of the medium in the chamber between a first position for a first pressure and a second position, where the second pressure is higher than the first pressure. In the second position a part of the stud protrudes further from the chamber than in the first position, The stud unit also contains a heating element (22) adapted to heat the medium so that the pressure in the chamber is adjusted between the first pressure and the second pressure.