4WD vs AWD – The Difference Explained
These days, more and more vehicles are described as ‘AWD’, and there is widespread confusion around this term.
Technically speaking, AWD simply refers to any vehicle which has the capability of powering all of its wheels. Therefore any 4WD is also an AWD, as it can be set to drive the four wheels (or axle ends, as we learned above).
However, when a vehicle is marketed as an ‘AWD’ – it means something else. When you see ‘AWD’ it simply means that the vehicle uses four-wheel drive all the time, instead of only when the 4WD option is engaged by the driver.
By Vauxford – Own work, CC BY-SA 4.0
AWD vehicles can be driven by all four wheels at all times because they have an extra, central differential (as we saw with Diplock’s traction engine at the start of the last century). The purpose of this differential is to allow the front and rear propeller shafts to spin at different speeds, thus allowing the front and rear axles to turn at different speeds when going around a corner.
This extra diff therefore overcomes the problem of ‘binding’ or ‘wind-up’ —an issue many of you offroaders will know all too well. This problem doesn’t occur on slippery surfaces, as the wheels are able to slip, but when turning a corner on a road or grippy surface with 4WD engaged, a huge amount of pressure is put on the drivetrain leading to damage or problems with steering. This is why ‘part-time’ 4WD should always be disengaged when not offroading.
This video explains it all very well:
For real offroading, a 4WD is much preferable to an AWD. As you’ll well know, in many situations having the two axles ‘locked’ is useful. So, while AWD can give fantastic grip on roads, and even when cornering on slippery surfaces, part-time 4WD is the system of choice for those who want to traverse the really difficult terrain.
