Wheel for pedal-assisted bikes, comprising: - at least a fixed structure associable with the frame of a bike having a driving pedal crank; - at least a circle element (10, 11, 12) mounted on said fixed structure in a rotatable way around a main rotation axis; - at least a propulsion disc mounted on said fixed structure in a rotatable way and connectable to said driving pedal crank; - motion transmission means (14, 15, 16) for the transmission of the rotary motion from said propulsion disc to said circle element (10, 11, 12); - at least a speed gear device included in said motion transmission means, said speed gear device being suitable for changing the motion transmission ratio from said propulsion disc to said circle element (10, 11, 12); and - at least an electric motor (54, 55) associated with said fixed structure and suitable for cooperating with said propulsion disc to motorize said circle element (10, 11, 12); wherein said speed gear device is substantially coaxial to said main rotation axis and comprises: - an annulus gear with internal teeth, associated with said propulsion disc; - at least a first group of planet gears (18a, 18b, 18c, 18d), made integral with each other and having a different number of teeth, of which at least one primary planet gear engaging with said annulus gear; - a planet carrier body (19, 20, 21) which supports said first group of planet gears (18a, 18b, 18c, 18d); - a second group of sun gears (22a, 22b, 22c, 22d), having a different number of teeth and engaging with a respective planet gear (18a, 18b, 18c, 18d), of which at least one primary sun gear engaging with said primary planet gear; and - a locking device (23, 24) for the selective locking of said sun gears (22a, 22b, 22c, 22d), suitable for preventing alternately the rotation of only one of said sun gears (22a, 22b, 22c, 22d) and to release the rotation of the remaining ones, the transmission ratio between said annulus gear and said planet carrier body (19, 20, 21) being established by which sun gear (22a, 22b, 22c, 22d) is locked, the wheel for pedal-assisted bikes being characterised in that said speed gear device further comprises a solidarization mechanism (28, 29) suitable for making said annulus gear integral with said planet carrier body (19, 20, 21) supporting the group of planet gears (18a, 18b, 18c, 18d), wherein said solidarization mechanism (28, 29) is configured to be placed in a coupling position in which the annulus gear is made integral with the planet carrier body (19, 20, 21) and the rotation of all the sun gears (22a, 22b, 22c, 22d) is released, and in an idle position in which at least one sun gear (22a, 22b, 22c, 22d) is locked. - at least a fixed structure associable with the frame of a bike having a driving pedal crank; - at least a circle element (10, 11, 12) mounted on said fixed structure in a rotatable way around a main rotation axis; - at least a propulsion disc mounted on said fixed structure in a rotatable way and connectable to said driving pedal crank; - motion transmission means (14, 15, 16) for the transmission of the rotary motion from said propulsion disc to said circle element (10, 11, 12); - at least a speed gear device included in said motion transmission means, said speed gear device being suitable for changing the motion transmission ratio from said propulsion disc to said circle element (10, 11, 12); and - at least an electric motor (54, 55) associated with said fixed structure and suitable for cooperating with said propulsion disc to motorize said circle element (10, 11, 12); - an annulus gear with internal teeth, associated with said propulsion disc; - at least a first group of planet gears (18a, 18b, 18c, 18d), made integral with each other and having a different number of teeth, of which at least one primary planet gear engaging with said annulus gear; - a planet carrier body (19, 20, 21) which supports said first group of planet gears (18a, 18b, 18c, 18d); - a second group of sun gears (22a, 22b, 22c, 22d), having a different number of teeth and engaging with a respective planet gear (18a, 18b, 18c, 18d), of which at least one primary sun gear engaging with said primary planet gear; and - a locking device (23, 24) for the selective locking of said sun gears (22a, 22b, 22c, 22d), suitable for preventing alternately the rotation of only one of said sun gears (22a, 22b, 22c, 22d) and to release the rotation of the remaining ones, the transmission ratio between said annulus gear and said planet carrier body (19, 20, 21) being established by which sun gear (22a, 22b, 22c, 22d) is locked,