between the end of the radially inner face of the support s axially closest to the seat 13 u2032 and the middle of the face the axial distance v x separating the mid axis of the protuberance 30 which is also the mid axis of the groove 115 from the end of the support seating zone 112 oriented to the exterior of the vehicle is between 0 1 and 0 2 times the axial width 1 of the support s first this is to have better centering of the support on the seating zone 112 second this is to minimize the length of movement under compressive force of the protuberance on the support although the circumferential elasticity of the protuberance 30 allows easy fitting of the support on the rim bearing surface 11 fig2 presents in side view a tool according to the invention this tool 40 for fitting tire beads and tread supports comprises an elongate shaped bracket 41 with a substantially cylindrical section of axis a a finger 42 a pressing roller 43 and a stop 44 this tool also comprises at one end a first fixing projection 410 adapted to snap into a tool support not shown the finger 42.