THE "RUN-FLAT" TYRE

Evening Star, Issue 25638, 12 November 1945, Page 2

THE "RUN-FLAT" TYRE

WAR-TIME INVENTION

The rubber industry conrtibuted many valuable aids to the war effort of the Allied Nations. For security reasons, details of many of the inventions have not been published heretofore, but now that victory has been won, it is permissible to make public interesting facts relative to some of these war-winning devices. One of the most interesting is the lighting tyre, technically known as the " R.F." or run-flat tyre. With the advance of mechanised fighting with pneumatic-shod vehicles, etc., tyro manufacturers throughout the world endeavoured to produce a pneumatic tyre that would withstand damage .from enemy action, except a direct shell hit, and still carry on the fight and be capable of mobility until the action ceased and the unit could withdraw for repairs. : The approach to this problem at first sight, naturally, was to find a substitute for air, and this led to the de\-elopment of all kinds of rubber fillers and sponge rubber inserts. The German bullet-proof tyre consisted of a hard rubber filling with small air spaces for compression. These experiments failed because of the heat factor, which would reach such a degree as to melt and destroy the insert and the cover.

The problem was tackled by Dunlop technicians from an entirely different angle, and the very simplicity of the invention contributed considerably to its success. In fact, so successful did the method prove in early operations that the British War Office adopted it as standard on all fighting vehicles, and passed on the details, of manufacture to the United States War Department, the outcome being that the United Nation's tyre manufacturers adopted the principle in their " 11. P." tyres.

The •' R.F." tyre is made exactly the same as a standerd tyre with the addition of an inner rubber liner of •Mn to lin thickness, according to size, moulded with the tyre so as to become an intergral • part of the casing. The tube is made of standard thickness from Jin to lin smaller in diameter of section.

When penetration occurs through machine-gun bullets or shell splinters, the air naturally is released, but the reinforced rubber wall is stiff enough to sustain the load without air. When the air pressure is released, the deflection is increased .and this causes an increased heat build-up which, limits further operation to within 50 miles before failure occurs, but this distance has proved more than sufficient to enable the fighting unit to complete its job and retire for repair. When a standard tyre is deflated during motion, the pressure of the beads on the wheel flanges is released, causing the tyre to creep on the rim. To overcome this problem with the "R.F." tyre, the wheels were manufactured in two halves, and are known as split wheels. A heavy rubber bead spacer is fitted between the bands, which is one-half inch wider than the normal bead toe width. This bead spacer is compressed when the two halves are bolted together, and exerts sufficient pressure on the beads to prevent creeping when deflation occurs. Many thousand? of " R.F." tyres have been manufactured in Australia and sent to various theatres of war.