The main advantage of a limited slip differential is shown by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely—the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, and thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use, such as driving in mud, off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the angular velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some traction available on at least one of the wheels.
Two main types of LSD's are commonly used on passenger cars; torque sensitive (geared or clutch-based or cone-based as shown in figure at top of page) and speed sensitive (viscous/pump and clutch pack). The latter is gaining popularity especially in modern all-wheel drive vehicles, and generally requires less maintenance than the mechanical type.
