In automotive design, a RR, or Rear-engine, Rear-wheel drive layout is one which places both the engine and drive wheels at the rear of the vehicle. In contrast to the RMR layout, however, the center of mass of the engine itself is actually past the rear axle. This is not to be confused with the center of mass of the whole vehicle, as an imbalance of such proportions would make it impossible to keep the front wheels on the ground.