An all-terrain vehicle (ATV) has a subtransmission detachably fastened to an engine casing. The engine crankshaft includes a drive pulley connected via a belt to a driven pulley in the subtransmission, thus providing a continuously variable transmission (CVT) between the engine crankshaft and the subtransmission. The subtransmission includes a 2WD-4WD selector mechanism to select two-wheel-drive or four-wheel-drive and also includes a transmission selector mechanism to put the vehicle in park, neutral, reverse, high-speed drive or low-speed drive. By disposing these selector mechanisms in the subtransmission, mass centralization is improved relative to prior-art drivetrains wherein the 2WD-4WD selector mechanism connects to the front differential. When operating in 2WD mode, the drivetrain does not waste energy rotating the front drive shaft, as in the prior art.