Tire having low rolling resistance

A tire comprising:

• two beads intended to come into contact with a mounting rim, each bead comprising at least one annular reinforcing structure defining a median plane perpendicular to an axis of rotation of the tire and situated equidistant from the annular reinforcing structures of each bead,
• two sidewalls extending the beads radially outwards, the two sidewalls meeting in a crown comprising a crown reinforcement radially surmounted by a sub-tread extending across an entire axial width of the crown reinforcement and itself surmounted by a tread provided with a tread pattern formed of elements in relief, the tread having, in each radial section, a first axial edge and a second axial edge;
• wherein the tread comprises:
• a central part made of at least one first rubber compound extending, in each radial section, on either side of the median plane, between a first axial end and a second axial end, the central part comprising at least two circumferential ribs, each rib being formed of a plurality of blocks separated by sipes so that a mean distance separating two adjacent blocks is less than 0.8 mm, a number of blocks in each rib being greater than or equal to 100;
• a first lateral part made of at least one second rubber compound, extending from the first axial edge of the tread as far as the first axial end of said central part, the first lateral part comprising at least one circumferential rib formed by a plurality of blocks separated by sipes so that a mean distance separating two adjacent blocks is greater than 0.8 mm and less than 5 mm, a number of blocks being less than the number of blocks that make up each of the at least two circumferential ribs of the central part;
• and
• a second lateral part made of at least one third rubber compound, extending from the second axial edge of the tread as far as the second axial end of said central part, the second lateral part comprising at least one circumferential rib formed by a plurality of blocks separated by sipes so that a mean distance separating two adjacent blocks is greater than 0.8 mm and less than 5 mm, a number of blocks being less than the number of blocks that make up each of the at least two circumferential ribs of the central part;
• wherein the at least one second and third rubber compounds have a value of tan δ at 23° C., at a frequency of 10 Hz and an elongation of 10%, which is less than 0.25;
• wherein the complex modulus G*(T) of said at least one first rubber compound is greater than the complex moduli G*(T) of said at least one second and third rubber compounds for all temperatures T greater than or equal to 0° and less than or equal to 60° C., and
• wherein each of said at least two ribs of the central part satisfies the following inequality:
• 0.90·EC/RC<SLEC/(2·π·RC)<1.10·EC/RC
• where EC denotes the mean radial thickness of the tread measured at each rib of the central part, RC denotes the mean radius of each rib of the central part, and SLEC denotes the sum of the mean circumferential widths of the sipes of each rib of the central part, and
• wherein each rib of the first lateral part and of the second lateral part satisfies the following inequality:
• 1.50·EL/RL<SLEL/(2·π·RL)
• where EL denotes the mean radial thickness of the tread measured at each rib of the lateral part, RL denotes the mean radius of each rib of the lateral part, and SLEL denotes the sum of the mean circumferential widths of the sipes of each rib of the lateral part.