Rocker arm for a bicycle gearshift, comprising: an inner plate and an outer plate ; an upper wheel and a lower wheel arranged between the inner plate and the outer plate and configured to engage a transmission chain , said upper wheel being rotatable about a first rotation axis (X1) and said lower wheel being rotatable about a second rotation axis (X2); said outer plate comprising a radially outer portion with respect to said first rotation axis (X1) provided with an active surface and with an auxiliary surface ; wherein said auxiliary surface is circumferentially after said active surface and wherein said active surface projects axially more internally with respect to said auxiliary surface ; wherein a first reference plane (P1) contains the first (X1) and the second rotation axis (X2) and a second reference plane (P2) contains the first rotation axis (X1) and is inclined by an angle (C), measured along a first circumferential direction (A) from the active surface towards the auxiliary surface , comprised between 20° and 60° with respect to the first reference plane (P1); the rocker arm characterised in that said auxiliary surface being arranged circumferentially beyond said second reference plane (P2) with respect to said first circumferential direction (A); wherein said active surface is arranged circumferentially beyond said second reference plane (P2) with respect to a second circumferential direction (B) opposite to the first circumferential direction (A) and wherein said active surface has a greater extension in the radial direction than the extension in the radial direction of the auxiliary surface . an inner plate and an outer plate ; an upper wheel and a lower wheel arranged between the inner plate and the outer plate and configured to engage a transmission chain , said upper wheel being rotatable about a first rotation axis (X1) and said lower wheel being rotatable about a second rotation axis (X2); said outer plate comprising a radially outer portion with respect to said first rotation axis (X1) provided with an active surface and with an auxiliary surface ; wherein said auxiliary surface is circumferentially after said active surface and wherein said active surface projects axially more internally with respect to said auxiliary surface ; wherein a first reference plane (P1) contains the first (X1) and the second rotation axis (X2) and a second reference plane (P2) contains the first rotation axis (X1) and is inclined by an angle (C), measured along a first circumferential direction (A) from the active surface towards the auxiliary surface , comprised between 20° and 60° with respect to the first reference plane (P1); the rocker arm characterised in that said auxiliary surface being arranged circumferentially beyond said second reference plane (P2) with respect to said first circumferential direction (A); wherein said active surface is arranged circumferentially beyond said second reference plane (P2) with respect to a second circumferential direction (B) opposite to the first circumferential direction (A) and wherein said active surface has a greater extension in the radial direction than the extension in the radial direction of the auxiliary surface . <EOS>