respective transmissions whose speed ratios i e the ratio of engine speed to wheel speed are independently and continuously variable such a vehicle may be steered merely by adjustment of the transmissions 39 ratios and may be highly manoeuvrable for instance by setting the transmissions to cause the vehicle wheels to rotate in opposite directions at equal speeds the vehicle can be caused to spin on the spot an operation referred to as a u201c zero turn u201d both of the vehicle 39 s transmissions incorporate in accordance with the present invention a brake mechanism 20 which is to be mounted adjacent to a driven vehicle wheel not shown and incorporates a wheel shaft 22 which carries the vehicle wheel and is the final output of the transmission the brake mechanism is mounted on a main housing 24 seen in fig6 to have at its front a mounting surface 26 to which a continuously variable transmission unit is to be secured with its output shaft protruding through an opening 28 in the housing wall to engage with a first gear 30 rotatably mounted within the main housing 24 the transmission unit is not shown in fig2 to 6 but fig7 and 8 show the main housing 24 mounted on the transmission unit 70 in this manner concealed within main housing 24 are a second idler gear not seen which meshes with the first gear 30 and a third output gear not seen which meshes with the idler gear and drives the wheel shaft 22 the first to third gears are of ascending sizes and form a gear train which provides a speed reduction at the wheel shaft 22 a brake disc 32 is seen in fig2.