THE LATEST IN TYRES.

Press, Volume LXVIII, Issue 20623, 12 August 1932, Page 6

THE LATEST IN TYRES.

J DEVELOPMENT IN | AMERICAi [ EXTREME LOW PRESSURE. America is all agog with the subject of the latest development in the tyre world, the application of the principle of the aeroplane tyre to motor-cars. 'The "New York Times" publishes an article by the editor of the "Tyres Magazine.'' He says the experts predict that within the year thousands of motorists will be riding on the new extreme low-pressure tyres. Vehicles of all weights will be carried on tyres requiring air pressures of from 101b to 201b, and providing the maximum of cushioning comfort. The new tyre is known by several trade names, including '' Super-Pneu-matic, "Streamline, Jumbo," ".^•uper-Cushion," "Air Balloon," and "AirwheeJ." Already it has cieated a problem similar to that caused by ihe introduction of the balloon tyre, in that the new tyre is being produced in a variety of sizes. The extreme low-pressure tyre is recognised as a logical step in tyre development. It is of a larger sectional diameter, lower rim diameter, and lower pressure than the familiar balloon. The extreme is reached with the elimination of ;,he wheel, the hub with attached brake drum taking up the entire .space between the axle and the tyre.

Evolution of the Balloon. Old-time motorists are t'amiH;>.- with the tyres that required an inflation pressure of 201b to the cross-sect.on inch. For instance, there was the 34 by 4 tyre that called for a pressure of 801b, the pressure insisted upon by the trye-makers if the purchaser was to obtain the 3500 miles of service guaranteed in the tyre.

Under-inflation was costly then because it created a sawing action in the cross-woven, threads with which the carcass of the tyre was construct? 1 and quickly brought a blow-out, a voad mishap accompanied by a bomb-liko rolcu3o of the air.

It was not a far step to the cord tyre, with larger cross-soci.ion, greater riding comfort, and with 551b to 601b pressure for the 4.4Hn easing-.. The cushioning effect of the cord w.ij 25 per cent, greater than that of the old tyre, and the mileage return was increased from 3000 to 8000. Bim diameter had also been reduced during the period of transition from tho fabric to the cord type, tho extreme during the former stage being 34 inches and (he popular size used with cord tyres being 23 inches. The balloon tyre made its appearance in 1922 and marked the next major step in tyre development. Abuse of inflation recommendations was responsible, in large measure, for the introduction of the balloon type. Tyre engineers decided to increase again tho crosa-scc-tional diameter of tho tyro, and, in order not to change the road clearance of the vehicle, they reduced the rim diameter proportionally.

The samo vehicle that formerly carried a 4in tyre now coull bo equipped with a IHin or Gin casing, which was inflated to 301b. Tt provided another 50 per cent, increase in cushioning effect. Tho original balloon lyres were modified somewhat to comply with automobile engineering requirements, but the basic principle of greater cushioning, smaller rim diameter, and lower pressure was retained. Mileage returns were built up from 15,000 to 20,000. . a Advantages Claimed. These are the advantages claimed by tyre engineers for the new type of tyre:— Better cushioning, which results in le3s fatigue for the driver and passengers. Less vibration transmitted to chassis and body, and, consequently, longer life of the car. Less likelihood of punctures and blow-outs, and less danger when they do occur. (At 121b and 181b pressure's tho large volume of air in the new tyre, when released through a cut or other cause, will escape relatively slowly nnd give the driver warning that the tyre is going flat.) Furthermore, in these largo section tyres the flexing action is so light at any given point in the carcass that failure from internal friction cannot occur. Also, punctures will be reduced because penetration of a tyro is easier as inflation is increased.

The larger road contact area of the extreme low pressure tyre results in a substantial increase in the effectiveness of brakes. For the same reason, traction is improved. The "snowshoe" effect of the larger contact area resists side-skid 10 a remarkable degree. Corners can be turned on wet pavements at higher speeds than was previously thought possible without sidewise slipping.