A method for correcting the conicity of a tread strip is described. The method includes the steps of extruding a tread profile having a right hand side, a left hand side and a chimney; measuring the thickness of the tread profile at the right hand side and the left hand side; calculating the mass of the tread on the left hand side and the right hand side; and adjusting the location of the chimney incrementally towards the side which is least in mass.