All-Wheel Drive Vs. 4WD


All-wheel drive and 4 wheel drive are probably the two most misinterpreted and misunderstood description of vehicle features in the automotive industry. To begin with all-wheel drive is a more road oriented way of putting traction on all four tires for better paved road handling and traction, but the reality is it just drives two wheels–one in the front and one in the rear, when torque or drive is coming from the engine in the most ideal on-road driving conditions.

The Subaru’s AWD system provides excellent grip on slippery road conditions

The Subaru’s AWD system provides excellent grip on slippery road conditions

There is no mechanical connection between the front and rear axle of the vehicle making the system not suitable for very difficult terrain. But thanks to modern computer controlled technology, drive is now directed to the wheel with the most bite on the road via the added program on the computer of the ABS system. This is called electronic traction control. In more advanced computer programs it also connects to the engine management system and actually cuts power from the engine to prevent slipping out of control. This is now called Dynamic Stability Control. These are all excellent safety devices but will not get you thru very difficult real off-road terrain.

Which brings us to the real 4WD–the kind that is used on really tough challenging terrain. Real four-wheel-drive also is no guarantee of successfully getting thru difficult terrain either. Though the front and the rear axle spin at the same speed, the moment one tire on each axle finds least resistance or traction, all the drive to the particular axle is sent to the wheel with the least resistance making forward progress near impossible in certain ground conditions. The reason why this is so is because the differentials on our axles are designed to prevent both left and right wheels from spinning at the same time when making a turn because left and right tires spin at different distances. If you follow this article we will discuss in the weeks ahead on how this is overcome by additional traction aids. For now let’s stick with the basics.

Aside from both front and rear axles are spinning at the same time in real 4WD or 4H (four-high meaning high speed, real 4WD’s also have a low speed ratio or 4L-L standing for low speed). Contrary to what the public may think, this low gear setting is designed to slow down the speed of the wheels so that the tires may have better bite on the off-road driving surface. So why then do we need low range when all one has to do is back off the accelerator for more bite or traction? Because low speed also doubles the twisting force on the wheels for more torque to overcome the driving surface resistance.

The 4x4 system of the Range Rover provides excellent traction even when there are no roads

The 4×4 system of the Range Rover provides excellent traction even when there are no roads

These basics are best understood by those who have the real need for real 4WD and by those who need to make an informed decision on purchasing a vehicle for a particular need. Till the next article, see you next time.


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