Abstract: The combination in a motor vehicle of a prime mover, a multi-speed main gearing provided with manual ratio selector means, a disengageable main clutch between the prime mover and the input of the main gearing, a driver-operated main clutch control having a first position in which the main clutch is engaged to transmit drive from the prime mover to the main gearing and a second position in which the main clutch is disengaged and which is normally assumed during ratio changes of said main gearing by said selector means, an auxiliary two-ratio gearing in series with the main gearing, and ratio control means for the auxiliary gearing connected with the main clutch control and manual selector means so that, with the main gearing in its highest ratio, each movement of the main clutch control to its second position not only disengages the clutch but also actuates the ratio control means to change the operative ratio of the auxiliary gearing.