to engage and disengage flywheel 11 39 and a second sprocket 15 39 when needed it will be appreciated that additional flywheels clutch assemblies and sprockets may be provided to this system sprockets 15 and 15 39 are each independently mounted on separate shaft sleeves 16 and 16 39 respectively said shaft sleeves being rotatively supported by said shaft flywheels 11 and 11 39 mounted on freewheeling shaft 13 thus function as freewheel flywheels to which all power from a power source is transmitted through the responsive rotation of freewheeling sprocket wheel 14 affixed to shaft 13 and linked by transmission means to the power source freewheeling sprocket wheel 14 in turn rotates shaft 13 it will be appreciated that the power source may conveniently comprise a pedal assembly operated by a human user an electric motor an internal combustion engine or the like all of the power applied to freewheel flywheels 11 and 11 39 plus the large rotational inertia and the speed stabilization effects are transmitted upon engaging either sprocket 15 or sprocket 15 39 via transmission means 52 or 53 respectively to a second sprocket means which may conveniently be gear or chain linked to a vehicle driven wheel sprocket 15 has clutch assemblies 17 and 18 mounted on its left and right sides for engaging and disengaging with freewheel flywheel 11 similarly sprocket 15 39 has clutch assemblies 17 39 and 18 39 mounted on its right and left sides for engaging and disengaging with freewheel flywheel 11 39 sprocket 15 and flywheel 11 or sprocket 15 39 and flywheel 11 39 may be engaged by the slight side way movement of the respective sprocket 15 or 15 39 in the embodiment as shown in fig1 clutch lever 19 moving from neutral to the.