All-Wheel Drive vehicles are designed to improve on-road drivability through the use of a system that powers all four wheels at all time (like a 4WD) but unlike the 4WD systems, the differential between the front and rear axles cannot be locked. The differentials do, however, have ability to limit slippage between the axles if a low traction situation is encountered. Usually this ability is provided with a differential known as a viscous coupling although more recently a similar outcome has been achieved by using electronically-controlled hydraulic or electro-magnetic ‘clutch’ systems.
AWD requires no driver action to implement driving power to all four wheels. The difference to a 4WD is that a 4-Low setting is not available. Due to the lack of a “low range”, AWD vehicles are much less capable in off-road terrain but have advanced on-road traction control to handle muddy, wet, ice slippery conditions. In fact, AWD vehicles are better equipped to handle on-road conditions
than a 4WD, such as a sudden slippery corner or sudden heavy breaking as there is twice the available traction.
Some AWDs are styled as cars and are more obviously designed for city or sporty driving. Other AWDs however are styled and promoted as SUVs however this in itself does not indicate that the vehicle is suitable for taking offroad. Buyer demand has created the SUV market where a higher seating position, and high-tech features deliver exceptional performance and safety through the AWD system and these vehicles might look like a luxury 4WD but are not.
Most AWD’s are termed “Softroaders as they lack the credentials to tackle truly offroad conditions.
At road speeds of anything about 30kph or above on a smooth surface AWD works well. However at lower speeds it handles poorly on uneven terrain, soft sand, mud, rough hill
The ground clearance of AWDs varies, but generally range between 165-220mm. The higher the ground clearance the greater capability to negotiate uneven and rough road conditions
, as the vehicle has a lessened chance of sticking or the underside being damaged.
“Softroaders” do not meet the 220mm ground clearance minimum that is required for offroad driving. The lack of sufficient ground clearance is an important factor in being capable of venturing off formed dirt roads and tracks. Whilst they might manage the dirt roads such as those found in National Parks and regional areas, they are not equipped for fire-trails, State Forests, or long-haul tracks, desert expeditions, or soft sand dunes on the beach or deserts.
Other factors such as lightly built suspension
components and little underbody protection would also limit the use of a Softroader in offroad conditions.
In addition if going offroad you should always carry a spare tyre/wheel that match the 4 rolling ones. Many AWDs including the luxury models such as Volvos, BMWs and Mercedes-Benz don’t have proper spares.
Tyres are yet another important consideration. Soft-roaders leave the factory on tyres that aren’t suitable for the bush where the heavier built casings of Light Truck tyres found of 4x4s make them more resistant to punctures.
Another problem the newer AWD's have is automatic CPU traction and brake assist. When driving on sand the traction assist will force spinning wheels (even if a slight spin) to jar on and off, much like the ABS when braking hard. When the Awd system creates this jarring effect on the wheels, it actually causes the vehicle to get bogged, in other words the Awd system will dig for traction, not a good idea on the sand.
Availability of parts, tyres and spares is a major concern when taking passenger vehicles into remote areas of Australia
and is one of the reasons that many 4WDrivers stick with the traditional truck body style of 4WD.
Pushing softroaders into many typical Australian pursuits stresses them beyond their design limits and results in mechanical trouble and heartache for the owners.