What is a limited slip differential (LSD)?

A limited slip differential (LSD) allows only a certain amount of slip between its two outputs (for example, wheels).  Once the slip threshold has been reached, it employs a mechanism to limit this slipping.

The limiting of slip is useful in traction limited situations such as on snow or mud.  In a traction limited situation, a normal open differential may allow the wheel with the least traction to spin away while the other wheel with good traction does not rotate.  A limited slip differential, once the slip threshold has been reached, will begin to transfer power to the non slipping wheel as well.

The purpose of the slip threshold in a limited slip differential is to permit a certain amount of normal slip that might be encountered, such as when making a turn in the vehicle.  Certain types of locking differentials do not allow this slip, or allow the slip to be controlled.

Limited slip differentials are typically more costly to product than their open differential counterparts.  Hence a typical passenger car will employ a normal open differential.  Some cars and trucks with towing packages or winter packages, or higher horsepower engines may employ a limited slip differential.