What is a LSD and what does it do?
 

What is a LSD and what does it do? and is it worth buying?

lsd is limited slip differential

A Limited Slip Differential is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In a car or automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.

The main advantage of an LSD is found by considering the case of a standard 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 at twice its intended velocity - the torque transmitted will be zero and the vehicle will remain stationary. In normal everyday use on typical roads, such a situation can usually be assumed to have a vanishingly small probability, and so a normal differential suffices. For more demanding use however, such as driving 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 velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels.

just to add a bit to that.......

If a differential was permanently locked, meaning both drive shafts spin at the same speed, your tires would both be traveling the same distance at all times. This is fine for going in a straight line, but when you turn, the inner tire travels less distance than the outside tire. So, the outside tire must speed up, which means the the differential must "slip" and let the outside axle go faster.

So....logic would tell me that limited slip differential will only let the differential slip a certain amount before it reaches a certain point at which it will not let the axles vary in speed any further.