Auxiliary drive for a trailer such as a caravan. Said drive consists of a drive unit with a gearwheel. Through linear movement of the drive unit relative to the chassis, said gearwheel can be brought into engagement with a ring gear fitted either on the brake drum of a wheel of the vehicle or on an auxiliary part such as a covering drum fitted over said brake drum. The ring gear preferably lies in a plane outside the plane bounded by the inside of the wheel.