Expandable radial carcass spare tire

Claim 1

A spare tire which is expandable by inflation, having a radial carcass reinforcement anchored to at least one bead ring in each bead and having a tread reinforcement formed of at least two plies of cables which are parallel in each ply and crossed from one ply to the other and form acute angles with the longitudinal direction of the tire, said tire having sidewalls with a sinuous meridian profile before expansion and a normal profile after expansion under the effect of the inflation pressure, characterized by the fact that the plies of the tread reinforcement are reinforced with cables whose curve of relative elongation under tension presents two consecutive segments, a first segment extending from a relative elongation of zero to a relative elongation of a=(sin α.sub.0 /sin α.sub.1)=(R.sub.1 /R.sub.0)(cos α.sub.0 /cos α.sub.1) and a second segment starting from the point of elongation a, the variation of the tensile force as a function of the elongation being low along the first segment and high along the second segment so that the cables, starting from the point of elongation a, have the tensile strength of ordinary cables, α being the acute angle of the cables of the tread ply with respect to the longitudinal direction of the tire, R being the radius of the tread reinforcement with respect to the axis of rotation of the tire, and the subscripts 0 and 1 appended to α and R corresponding to the unexpanded condition (zero inflation pressure) and the expanded condition, respectively, of the tire under the effect of the inflation pressure, the angle α 1 corresponding to the expanded condition of the tire being between 15° and 30°, and further characterized by the fact that the tire is vulcanized in unexpanded condition corresponding to the radius R 0 of the tread reinforcement and by the fact that in expanded condition the tread reinforcement has lengthened by a length 2π(R 1 -R 0 ) while its width has not changed.