Every car has a slip diff but with a few tweaks you can totally transform your cars performance in the wet and other low grip conditions.
In a recent track test a Megane 225 Sport with a Limited slip diff out performed a number of more powerful cars on a wet track which goes some way to show how important this often overlooked part of the car is.
What does a diff do? Go back to the days when you made your first axle from a pencil and 2 cotton reels.
When it went in a straight line all was fine but when the axles turns a corner the one of the wheels start to slip and lose traction. The wheel that covers the outer radius of the corner must rotate more than the one on the inside as it has a greater distance to travel.
Try it with a pencil and 2 pieces of round car for wheels marking out each complete revolution of the wheel.
In a car the diff takes the power from the engine via the gearbox through the prop-shaft and diverts it to the wheels according to the amount each wheel takes with the wheel on the outside radius of a corner taking the most as it rotates a greater distance. The problem you get with a road car though is that the diff will send more power to the wheel which is spinning fastest. If one wheel is on ice and the other grips all of the power will go to the wheel which has no grip and the car will be effectively stuck.
Enter the Torque sensitive slip diff. This will perform in the same way as a standard but will limit the amount of power going to one wheel to 65-80% depending on its design. This avoids the problem of the car getting stuck in low grip conditions and actually improves traction when going through bends in the wet.
We also have a torque activated (clutch type) LSD which senses the amount of load from the input and behaves as a 1 way 1.5 or 2 way limited slip diff which gives a pretty good compromise in all conditions. When under a full load the coupling is proportional and under low load conditions we are back to a fixed coupling.
Geared torque sensitive diffs are also available which do not look at the relative difference between the output shafts rather looking at the input shaft but have useful applications in FWD cars reducing torque steer, and on drift car settings allowing more predictable over steer although pro drifters use a clutch type LSD.
The electronically controlled slip diff is a recent development and uses the anti lock brake sensors to monitor independent wheel speed and uses braking to bring the wheel under control if it starts to slip.
When you have fitted a new LSD you must follow the instructions that came with it to break it in properly otherwise you may cause permanent damage to the diff. For motor sport and heavy fast road use, it is recommended of using a clutch type of LSD due to their solid construction and reliability.
Most of the time you will not notice that you have a high performance diff but under heavy load and especially in low grip conditions you will really start to appreciate this subtle modification and turn in some very impressive track times compared to more powerful cars with a standard diff.
In 4 wheel drive cars the diff gets more complex and can divert the power to the rear and front wheels depending on the amount of grip available so there is much more scope for altering the traction and handling characteristics of these cars.
In complex cars such as the Nissan Skyline the diff can make the car behave like a rear wheel drive until traction is lost and then around 20% of the power can be diverted to the front wheels. Join us in our friendly car tuning forum to discuss diffs in more details.
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