TYRE WITH IMPROVED TREAD

Tire comprising a tread which has at least one central rib (411-413) and two lateral ribs (421-422) which are separated by circumferential grooves (141-144), in which tire a first lateral rib (421) adjacent to the outer axial edge of the tread and at least one (and preferably each) of the central ribs have a first portion (4211, 4111, 4121, 4131) the axial width of which exceeds 2 % of the axial width of the relevant rib made and the depth of which is less than that of the relevant rib, from a rubber composition containing an elastomer and a reinforcing filler consisting predominantly of carbon black, and an axially adjacent second portion (4212, 4112, 4122, 4132) made of a rubber composition containing an elastomer and a reinforcing filler a minority proportion of which consists of carbon black, in which the rubber compositions that make up the second portion of the first lateral rib and the second portion of the central rib all have a tan 50 value which is higher than the tan 50 value of the rubber compositions that form the first portion of the first lateral rib and the first portion of the central rib, the tan 50 values being measured at a temperature of 0° C. and under a stress of 0.7 MPa.