A mounting and gearing system for power-assisted bicycles comprising a system frame 12 that mounts to brake posts 14 and to an axle clamp bolt 22 of a bicycle 21, an extension arm 3 use extension arm bolts 33 to bolt to an electric motor 1, that has square flanges at each end, so that one corner will pivot on a motor pivot tube 13 on the system frame 12, the extension arm 3 with adjustment slots 23 are used to vary the tension of a primary drive belt 18 that connects a motor pulley 2 and a clutch pulley 4, a clutch sprocket 10 is pressed on a roller clutch 9 that rides on a clutch shaft 8 supported by a pair of support bearings 7 that are sandwiched between a bolster plate 6 and the extension arm 3 using standoffs 5, the clutch sprocket 10 connects to a wheel sprocket 11 via a secondary drive chain 19, the wheel sprocket 11 is connected to a tire 20 via wheel spokes 28 and a wheel hub 27, the tension of the secondary drive chain 19 is adjusted using a support strut 17 that mounts on the standoffs 5 and a support strut mount 16.