A Revolution in Tyre Construction
A Revolutionary Construction for Unrivalled Performance
With its X tyre with radial casing plies, Michelin set out to conquer the world with a considerable advance in technology. Its revolutionary construction for the time had the special feature of separating the sidewall function from the crown function.
The first major innovation from Michelin, the radial tyre was first marketed as the "X" tyre in 1949. At that time, Lancia was the first car manufacturer to fit the X tyre as original equipment on the Aurelia model. From 1955 onwards, radial technology became more popular and the majority of European car manufacturers opted for the radial solution. The X could be fitted to cars of very different categories, from the original and popular 2 CV or Beetle to the fascinating Mercedes 190SL or Facel Vega.
The advantages of the radial tyre compared with the cross-ply tyre could be clearly seen in all areas :
- greater safety (road-holding, grip, braking)
- economical to use (double the mileage, considerable reduction in fuel consumption)
- increased comfort thanks to the flexibility of the sidewalls. In the Fifties, the superiority of the X tyre was such that a number of racing drivers adopted it, although Michelin was not officially involved in any racing.
Cross-ply: This cross-section shows the singleconcept structure of the cross-ply tyre. From bead to bead, four layers (at least) of textile fabric extend from one sidewall to the tread, going over to the other sidewall. The sidewalls and tread are not differentiated. The detailed picture portrays the overlapping cords.
Thesemake up a thick mass of innumerablesuperimposed layers which represent as many areas of friction.
A consequence of this is the appearance of "shearing" motions. The longitudinal crosssection shown on the bottom left-hand side illustrates the shearing effect between the superimposed layers.
Radial: One can easily see the specialisation of the functions of sidewall/casing and tread. The sidewalls are made up of single layer of textiles plies, and so are not affected by the "shearing" phenomenon. The textile layer, like the rubber layer covering it, is thin and is therefore flexible.
The considerable flexibility of the sidewalls results in better handling as well as fuel savings. As for the tread, it is made rigid through a triangulation effect brought about by combining the casing layer with two layers of steel cord bracing plies (3 for the X tyre). The rigidity of the crown reduces wear of the tyres and improves road-holding.