A drive arrangement (10) has first and second wheels (12, 14) and an endless loop member (16). The path of the member (16) is defined in part by a third wheel (18), between the wheels (12, 14). The wheel (18) is movably mounted so that the length can be changed for the path of the member (16) as it passes around the wheel (18), between the wheels (12, -14). Accordingly, the member (16) can be tightened or slackened around the wheels (12, 14), so that the wheels (12, 14) can be coupled to convey drive from one to the other, through the member (16), or disengaged, so that drive is not conveyed.