In Automobile design, an RR, or Rear-engine, Rear wheel drive, layout places both the engine and drive wheels at the rear of the vehicle. In contrast to the MR layout, however, the center of gravity of the engine itself is actually past the rear axle. This is not to be confused with the center of gravity of the vehicle itself, as an imbalance of such proportions would make it impossible to keep the front wheels on the ground.
This layout is typically chosen for a combination of several reasons. For optimal handling and to eliminate the phenomenon known as torque steer, the wheels which propel the car should not be the same ones that steer it. For optimum traction, the engine should be nearest to the driven wheels since the engine is typically the densest/heaviest component of the car. Thus, in a car which steers with the front wheels, it is better for the engine to be located in the rear of the car - either a RR or MR design.
The disadvantage of the RR configuration is that placing the engine outside the wheelbase creates significant problems for handling as, when the car begins to slide on a corner, the end of the car will tend to want to swing wide and overtake the front - especially under braking. This tendency is referred to as oversteer and creates potential safety issues in racing applications as well as for ordinary drivers on wet or icy roads, although such behavior is desirable in drifting, a motorsport based on intentional oversteer.