Abstract: An apparatus for mounting a pneumatic tire in a testing and/or measuring apparatus comprises first and second mounting rim portions for holding a pneumatic tire between them in an inflated condition, on a rotatable spindle. The mounting rim portions are carried in concentric relationship with respect to the axis of rotation of the spindle, the first mounting rim portion being slidable in the axial direction on a guide. A clamp non-rotatably clamps the first rim portion to the guide along which the rim portion is displaceable in a released condition. The clamp includes a clamping element which is disposed about the axis and which is deformable upon inflation of the tire by the tire-inflation pressure to form a positively locking engagement between the first rim portion and the guide.