First developments of the radial tyre go back to the year 1948, when Michelin achieved under the keyword 'X-technology' about twice the life of a conventional double-ply tyre. The radial-ply tyre combines a relatively hard,
low resistance tread with a more flexible side-wall. The advantages can be easily recognised if one has a look at a train wheel, the friction is so low, that if, when driving on a level track at, e.g., 160 km/h, the motor is
switched off, over a distance of 40 kms the train only loses 20 km/h of speed. However, a steel wheel, on a suitable rail, particularly when wet, also needs a terribly long braking distance. This means that one may not
exaggerate the hardening.
Rayon-cord is applied radially, from beading to beading. In addition, the tread is reinforced by two to three layers of vulcanised steel wire. They form a solid belt - hence the description radial-ply (belted) tyre. The (thread-
) angle between the material and the steel wiring is, in the case of radial-ply tyres, particularly obtuse, about 90°. Especially light-weight radial-ply tyres are produced with thinner side-walls and with synthetic layers
instead of steel belts.
The advantages over diagonal-or cross-ply-tyres are:
- lower rolling resistance,
- lower fuel consumption,
- better cornering,
better braking- and acceleration properties.
A disadvantage is, that the comfort suffers a little because the tyre is harder. For a class of vehicles, the principle of the radial tyre is problematic, the motorcycles. It need parts of the sidewalls at lean angles in the curve.
Therefore here the diagonal-ply tire has survived for a longer time, was then replaced by a special design that allows a curved surface differing from the car tyre.