Improvements in tubeless pneumatic tyres

733,936. Pneumatic tyres. DUNLOP RUBBER CO., Ltd. Nov. 11, 1953 [Nov. 27, 1952], No. 30034/52. Class 144 (2). An air impermeable tubeless pneumatic tyre 1 is sealed at its beads 4 by a resilient rubber annular bead spacer 3 which sealingly co-operates also with inextensible beaded edge portions 18 of a horse-shoe section safety diaphragm 14 formed of rubberised filamentary material, the annular spacer 3 being provided with a tyre inflation valve, and the diaphragm 14 having a restricted aperture 19 for communication between the inner and outer chambers 15, 16 formed thereby. As shown in Fig. 1 the diaphragm beads 18 are received in circumferential grooves 13 in the spacer 3 which is formed also with flexible tongues 5 to extend between the tyre and diaphragm beads at each side to effect a seal therebetween. The spacer 3 may have reinforcing bead wire inserts 12 and in an alternative arrangement, it may be of shorter axial width than as shown in Fig. 1 to allow the diaphragm to extend radially to seat on the rim and be clamped against the tyre beads by the spacer 3. Fig. 2 shows a further arrangement wherein a spacer 23 is normally of arched section which is flattened on tyre inflation to press wedge-shaped lateral projections 24 thereon into sealing engagement between the chamfered bead toe 21 and the wheel rim. The diaphragm beads may, if desired, be formed integrally with the spacer 3. In another arrangement, the spacer 3 may be formed as a separately inflatable annulus with an inextensible reinforced outer periphery. To permit of quick inflation of both chambers 15, 16 whilst providing for a restricted air flow on blow-out of the tyre, the communicating aperture 19 in the diaphragm may be fitted with a flow-restricting valve of the centrifugally operating magnetized ball type.