Every week, Exhaust Notes will pick out an industry, technical or obscure term from the automotive world and give you the lowdown on what it means and how it’s used. Already know the answer? Congratulations, you’re ahead of the game.

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This week’s term: limited-slip differential (LSD)

Since an LSD is a particular type of device, let's get the quick definition of a differential out of the way: A differential transmits engine power to the wheels, and allows the wheels to rotate at different speeds even while being driven with equal force. This is especially handy when cornering, since whichever wheels are on the inside of the turn travel a shorter distance. For comparison, think of driving a standard Go Kart (which typically does not have a differential); the skidding and fishtailing are the result of the discrepancy that occurs when the engine provides the same force to wheels that must rotate at the same speed while traveling different distances.

Limited-slip differentials were originally meant for vehicles with higher performance demands, such as off-road vehicles or race cars. That's because regular differentials fail, for example, when one wheel is off the ground or spinning in mud -- since torque is divided equally among both wheels (including one that has no contact with the ground), the amount of power provided is not enough to move the vehicle. Without getting too technical (there are various types and permutations of LSDs), a limited-slip differential limits the disparity between the angular velocity of the wheels -- meaning, for example, that if one wheel has no contact with the ground, the torque is not divvied up equally to that wheel; rather, it remains directed at the wheel that has contact with the ground, thereby preserving "useful" torque and keeping the vehicle moving.