The present invention relates to compositions for elastomeric compounds for tyres, comprising modified diene polymers (A1) terminated with at least one tetrazole group (E) comprising at least one 2,5 disubstituted tetrazole which may be activated by heating, tyre components and tyres for vehicle wheels comprising them. Advantageously, the present modified diene polymers (A1) impart to the compounds lower hot hysteresis and reduced Payne effect and, consequently, lower rolling resistance and wear. Furthermore, the present polymers do not exhibit the processability problems shown by conventional functionalised diene polymers, with high affinity for white fillers.

A bimetallic catalytic system consists of the metallic components of formulae RLi and Ca(AR.sub.y).sub.2(L).sub.x in which: R represents a substituted or unsubstituted C.sub.1-C.sub.10 aliphatic radical, a substituted or unsubstituted C.sub.6-C.sub.20 aromatic radical or a substituted or unsubstituted C.sub.1-C.sub.10 heteroaliphatic radical; A denotes N or C; y has the value 2 when A is N and the value 3 when A is C; each R represents a hydrogen atom, a substituted or unsubstituted C.sub.5-C.sub.10 aliphatic radical, a substituted or unsubstituted C.sub.6-C.sub.20 aromatic radical, a substituted or unsubstituted silyl radical, a C.sub.1-C.sub.10 aliphatic radical substituted by at least one substituted or unsubstituted silyl radical, a C.sub.6-C.sub.20 aromatic radical substituted by at least one substituted or unsubstituted silyl radical; L represents a ligand; and x is a number ranging from 0 to 4.