Traction Control vs Conventional Differentials

Traction Control vs Conventional Differentials

Traction Control versus Conventional Differentials by Gerald O’Brien

We’ve all heard about Traction Control (TRC) and how it seems to improve the safety and handling of the mode of transport that has it. Why mode of transport and not just 4×4? Because virtually any mode of transport that has a wheel may or may not have Traction Control, depending on the manufacturer of the transport. For the sake of this article, let’s talk 4×4 and not motorcycles or passenger sedans – although they would all work in a very similar way, except on fewer wheels.

Then to complicate matters even more, not all 4×4’s have Traction Control as standard original fitment. But why not if its’ supposed to be so good and improves the safety and handling of the vehicle that we drive? There’s a plain and simple answer to that: it’s the cost factor. Having Traction Control pushes up the manufacturing cost of the 4×4 by quite a bit which, say, in the case of a double cab where manufactures fight each other tooth and nail for market share, that extra cost would push their vehicle far beyond the cost of their competitors. If all the manufacturers fitted Traction Control at the same time there would be no problem; in theory any way.


The conventional 4 wheel drive –No Traction Control.

Whilst driving along a relatively flat surface where traction is good, each differential (i.e. both the front and rear differentials) will each receive roughly 50% of the available 100% power being sent out from the Transfer Case (4×4 Gear Box) to each differential. Now, once the power which is being transmitted via the Prop Shaft to the differential arrives at the centre portion of the differential, the centre portion distributes roughly half of that power to each of the two wheels on that differential. In other words, each of the 4 wheels on the 4×4 are now receiving roughly 25% of the total power available at that time; hence the name 4×4 (4 wheels and 4 driving wheels). Two of the functions of the centre portion of a differential are:

1.)    To allow the speeds between the left- and right hand wheels to vary whilst cornering. The inside wheel needs to rotate at a slower speed than the outside wheel, which has a longer way to travel to get around the same corner. If the wheel speeds were not allowed to vary between left and right, the vehicle would constantly travel in a straight line wherever it went.

2.)    The second function of the centre portion is that it sends all the available power to the wheel with the least amount of resistance. This will happen to each differential at the same time. Have you ever noticed how only one wheel on an axle spins when getting stuck or bogged down? This is simply how the differential works and there’s nothing that you can do about it.

A 4 wheel drive vehicle becomes truly stuck when, for some or other reason, traction is lost on two wheels at the same time: one on either differential, usually diagonally opposite each other; which means that all the available power is now simply wasted by spinning those two wheels and there’s very little you can do about it. Diff locks are available, but we’re not going into that in this article.

Now bring in Traction Control.

All the 4×4 ‘s that have Traction Control also have two differentials, which just happen to work in exactly the same way as the vehicles which don’t have Traction Control work.

The big difference between a vehicle with TRC as opposed to a vehicle which doesn’t have it, is not in the mechanics or construction of the differential but rather the ABS braking system.

Simply put; a vehicle fitted with TRC has an ABS sensor on each wheel that is linked up to the ABS Actuator, which in turn is connected up to the vehicles ECU (computer box). Now what happens with TRC is that, when a vehicles traction is lost on either one or two wheels, the sensors on each wheel senses which wheel on which (or both) differentials are spinning and through the ABS system is able to apply brake pressure to the spinning wheels. By breaking the spinning wheels, it means that the power is now only able to travel in one direction, and that is to the opposite wheel – which is not spinning. The reason why the other wheel is not spinning, is because it has traction and the spinning wheel doesn’t have traction, or most certainly less traction that the non-spinning wheel.

So in a nutshell, Traction Control sends the power to the NON-spinning wheels.
It must be noted that, when Traction Control clicks in, it doesn’t simply stop the spinning wheels from spinning. It locks and releases the brakes at a rapid rate until such time that the vehicle has driven free from the obstacle. Traction Control is not selected on demand by the driver. It operates automatically in any condition at any time and on any surface. Having said that; it is important for the driver of a vehicle to be up to date with the operational functions of that vehicle, since there are quite a few operating options available between different models and manufacturers.

That’s why we have 4×4 training centres. They are always available to advise and assist whenever necessary.