BOGGED: USE THEORY TO GET UNSTUCK

Question: ‘Can we use a single pair of MAXTRAX to get out of a bog instead of a full set of four?

Understanding how your vehicle’s differentials work will make your time offroad much easier.

To answer this, we really need a proper understanding of how a 4WD driveline works.

Everyone knows that in a 4WD, we have a front and a rear differential, as well as a transfer case. The driveline provides drive from the engine to the wheels.

When turning corners, the wheels of the vehicle travel different distances, so the axles need a way of providing the drive to the wheels, but they still need to be able to allow the wheels to travel different distances and speeds.

This is when the differential comes in.

There are a few different types of differentials. An open differential, a LSD (limited slip differential) and we also have differential locks.

 

TYPES OF DIFFERENTIALS

AN OPEN DIFFERENTIAL will have only one driving wheel. Which wheel being driven will depend on the traction to the wheel, and when turning corners, an open diff allows one wheel to travel further and faster than the other through the spider gears.

A LSD has a set of clutches in with the spider gears. These clutches provide grip to the wheels, or at least the axles that sit in the spider gears.

In a straight line, they will transfer drive through to both wheels. When turning, they will grip, but once the force overcomes the grip of the clutches, it will allow slip and the wheel to turn at different speeds when cornering.

A DIFFERENTIAL LOCK is a solid connection for the wheels. Operated electronically through magnets, or electronically though vacuum solenoids. It creates a solid lock with no slip at all.

When cornering on a solid concrete surface, it will cause the driveline to bind up and the tyres can slip on the road. In some cases, it can cause driveline damage, as the wheels will not be able to turn at different speeds.

When travelling at higher speeds, a differential lock can cause a vehicle to become unstable when cornering due to the tyres slipping on the road.

 

WHAT’S A CENTRE DIFF?

So, a differential splits the power from the engine to the wheels, but we also have a centre diff lock in the transfer case. What does this do?

There is a differential in the transfer case, which delivers drive to both the front and rear differentials via the tail shafts, but when the centre differential lock is engaged, it locks the tail shafts together providing a 50-50 split to the front and rear diffs.

 

WHAT DOES ALL THIS ACTUALLY MEAN?

Well with an open differential, power is provided to the wheel that is the easiest to spin.

If you can imagine you are in your 4WD and you are bogged; one rear wheel is spinning, the other is on solid ground, with one front wheel spinning and the other on the ground.

Even though you have one wheel on the ground with traction, you are actually stuck because the power is provided to the wheel that is the easiest to turn.

 

HOW ABOUT WITH AN LSD?

It is important to mention here that a LSD is used only as the rear differential, and the front is usually an open differential.

In a bogged situation as above, the LSD clutches will also be overpowered fairly quickly and will split, which will also result in you being stuck. Yes, there is more chance of getting out but not a lot.

 

DIFFERENTIAL LOCKS

With a differential lock, this is a different story, as when you engage the diff lock it will lock the wheel solid providing 50-50 to each wheel.

In this case, there is more chance of getting out as the wheel that is on the ground and has traction will get drive and will hopefully push the vehicle forward.

Now it is important to mention that a lot of new vehicles now have traction control. This can change the stakes, somewhat.

 

TRACTION CONTROL

When the vehicle senses a wheel rotating and the other wheel not rotating, as in the situation above, it actually will break the rotating wheel, which will then cause the differential to actually send drive to the wheel on the ground. Depending on your vehicle, this can actually be very useful in situations like the above.

Let’s change the situation a little. Let’s say you have both rear wheels spinning, or both front wheels, it doesn’t matter really, just the front or rear wheels are spinning and you are stuck.

The transfer case (centre differential) will also provide power to the front or rear through the easiest path. So again, even if you have one axle on the ground, the fact that the other axle is spinning means you are again stuck.

At this point you can push the button for the centre differential lock and lock the tail shafts. This will provide 50-50 drive to both tail shafts, which will then provide drive to the axle that is on the ground and give you a chance of getting out.

It is also worth mentioning that in most 4WDs, when you select low range it will automatically apply the centre differential lock.

 

PUTTING IT ALL TOGETHER

So coming back to the original question… is it possible to just use a pair of MAXTRAX instead of a full set to get you out of a bog?

Well the answer is yes… depending on the situation and whether you understand how to use your 4WD.

If it is the rear wheels that are spinning and you have an open differential or a LSD, you could chock up the spinning wheel with a MAXTRAX and put the other MAXTRAX under the wheel on the ground. Then engage the centre differential lock and slowly try to drive forwards.

Another option could be to try to chock up the spinning wheels with the MAXTRAX to provide them some grip, again engage the centre diff lock and then try to drive forwards.

If the wheel on the ground starts to spin, then you may have to revert back to fitting the MAXTRAX to only one axle.

If you have traction control, then it does become a little simpler, as you can fit the MAXTRAX under the wheel that is not spinning to give it much more traction, then engage the traction control and centre diff lock and start to drive forwards.

The spinning wheel should start to spin, then the traction control will brake it, sending drive to the wheel with the MAXTRAX, and hopefully moving you forwards.

The differential lock is easier to work with in this instance, as it locks the wheel solid. You can simply fit up the MAXTRAX to the wheel on the ground, engage the centre diff lock and then try to move forward.

So, you can definitely get unstuck with just one pair of MAXTRAX, but having a set of four is much better, and nothing is more useful than having a proper understanding of your 4WD’s systems.