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"X" Stands for Longer Life
Page 87
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ANEW tyre to be known as the X has been developed by the Michelin Tyre Co., Ltd. It is designed to improve road-holding and, reduce deterioration under the effect of load and speed. The tread is also less affected by abrasion or wear. It has fewer plies than the conventional cover, thus reducing potential internal heat, and there is no bias angle.
The X cover has the normal three main sections, comprising the bead, case and tread, but the function of each is independent. The case, which is a combination of textile and metal, has four or six plies of textile, in which the cords art placed transversely at 90 degrees across the carcass.
On this foundation is the first layer of metal cords, which are built transversely on the textile base, followed by two more layers of metallic cord at 45 degrees in diagonally opposite directions. The textile plies in the wall carry the load flexibly, and as their action has no influence on the tread band, they are extremely elastic. At the same time, the tread is supple longitudinally, but greater rigidity is obtained transversely because the steel wires eliminate any internal deformation of the tread surface, thus permitting roll without creeping.
Several hundreds of X tyres have been on test in Britain for two years and users' reports indicate exceptional road holding, greater flexibility and a lower rate.of wear. The Michelin factory at Stoke-on-Trent is already producing the 7.50-20-in. (34 by 7-in.). cover, which has 10-ply rating load capacity, and it is planned to introduce an 8.25-20-in. 12-ply rating cover within a short period. The ply rating has no connection with the number of textile or steel plies in the construction of the X tyre. The new tyres are subject to the same load and inflation pressure as a normal textile cover, but because of greater flexibility they should riot be paired with a textile or Metallic type on a twin rear wheel.