Thursday April 3 2014

Pocket Dictionary: Limited slip differential

Part of a car’s limited slip differential.

Part of a car’s limited slip differential. NET PHOTO 

By Peter Mutimba

Last time, we explored an open differential and its uses. Today, let us look at its biggest disadvantage and how to solve it. To recap, a differential is that device under the car that enables it to go around a corner by allowing the wheels to turn at different speeds.

Essentially, a differential is able to do what it does by applying the same amount of turning power to both wheels. Keep that in mind for a second, because it is the very source of its problems. In dry conditions, where there is proper contact between the road and the wheel, the turning power is determined by the engine.

Basically, the harder you step on the accelerator, the more turning power will go to the wheels. That is all well and good. But in wet or slippery conditions, where there isn’t too much contact between the wheel and the ground, or in case you fall in a ditch and one tyre is in the air, the differential will supply just enough turning power to the wheels to the point they begin to slip and spin aimlessly.

Think of the differential as a mother. She will give a child just enough food, to the point where the child begins playing with it or spitting it out, and then she will give no more. Let us go back to the differential. If it is feeding the tyres 10 torques, 20, 30, and suddenly one begins to slip, it is not going to supply one more Newton metre of torque however hard you step on the accelerator.

Now is a good time to remember that the differential makes sure that both wheels get the same amount of turning power. You agree that it takes very little turning power indeed to make a wheel which is in the air spin around aimlessly. That is the same exact amount of turning power that will go to the other wheel. Think of it as, zero times two is still zero. You are still going nowhere.

So, engineers came up with a solution: Limited slip differential. According to, a limited slip differential is a device which automatically reduces the loss of drive which can result from spinning wheels on one side of an axle.

It does its job of allowing the car to turn in the corner, but once one of the wheels begins to spin, it directs more power to the wheel that has proper ground contact or traction. If you drive a vehicle daily, eventually you will be faced with less-than-ideal road conditions, and a limited slip differential may come in handy.