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Q. What does a Limited Slip Differential do?
A. An LSD is installed to maximize wheel traction. These benefits are seen most readily in competition, particularly where the car is attempting to accelerate on the way out of a bend or corner.
Under normal driving conditions, standard diff tries to equalize the driving torque between the two driving wheels by varying the relative speed of the wheels. This works well on an even and regular surface. However, when the road surface under the two wheels is significantly different or the weight loadings differ (such as when cornering), one wheel has a reduced ability to transmit the torque to the road surface and traction is reduced or completely lost by that wheel.
In a normal differential if traction is lost by one wheel the differential will try to turn that wheel at a greater speed until it reaches a speed approximately equal to twice the speed of the vehicle and not driving torque is applied to the other wheel. This creates a " no drive" condition.
All LSDs reduce this lack of drive condition. LSD’s work by clutching the differential sidegears to the differential cage. The clutch unit will have a relatively small amount of grip when no power is being transmitted, allowing the gears to move within the cage and so the whole unit operates more-or less as a standard diff. When full power is applied, these clutches become heavily loaded and the amount of clutch grip increases
substantially, effectively locking up the whole internal diff cage assembly and making the car behave as though it has a solid axle from wheel to wheel. At part throttle openings, the effect will be somewhere between these two extremes. If you think about all this, you will see that the term “limited slip” is an accurate description of its operation.
Under normal road conditions there will be no change in driving characteristics.
Q. How can I tell if I need an LSD?
A. If your car is not fitted with an LSD, you will notice a tendency for the engine to rev faster in the corners than on the straight for a given speed, and to leave only one wheel mark off the starting line. This indicates that one of your wheels is spinning and that your available traction has been greatly reduced. If your vehicle seems to "go nowhere" under power or people comment on smoke from your inside rear tyre, there is no doubt that your traction, can be improved by fitting an LSD. This translates directly to more BHP on the road!
In general, the LSD provides improved traction in all conditions, and makes for a lot more fun under slippery conditions. If you are likely to use your vehicle to its limits you will get good value from an LSD.
Q. Will an LSD affect handling?
A. Handling is enhanced with an LSD as the effect when the rear wheels lose traction is much more even and controllable. Up to that point, the LSD will accentuate a slight understeer under power, oversteer on overrun. This provides a the opportunity to “fine-tune” your line through a corner with the use of the accelerator.
Q. How do I tell if I already have an LSD?
A. Raise one of the drive wheels off the ground with the hand brake off and the car out of gear. Try to rotate one wheel in the forward direction. If it rotates freely then it has a standard differential. If it doesn’t move, or moves with difficulty then the diff is a limited slip type.
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