We like
Extra grip, balance, lack of torque steer, price premium

Room for improvement
Thumpy suspension, no brake assist, visual subtlety

ONE way to make our roads safer would be to legislate that all-wheel drive be a standard feature of all cars.

Expensive, maybe, but there’s little doubt that all-wheel traction is safer than two-wheel traction. Particularly in sedan cars, and especially in slippery conditions.

Generally, a four-wheel drive car will stick to its line when accelerating around a slippery corner.

It will also be happy to move away cleanly from a standing start in conditions that would have a front or rear-wheel drive car either uselessly spinning its front wheels, or slewing sideways as the rear-end scrabbles for traction. AWD is the best way to get the most out of a powerful engine.

Indeed, there are some indications that 4WD sedans might become extremely common, as people like Subaru, Audi, Volkswagen, Mitsubishi – and Volvo – take up the all-wheel option.

There are many ways of making a sedan car all-wheel drive, dictated by things like the original drive system (front or rear-wheel), the placement of the engine (north-south or east-west) and the amount of space available underneath to run the drive shaft through to the rear wheels.

Then there is the method all-wheel systems can use either a third differential between front and rear axle, a multi-plate clutch system, or a viscous coupling to apportion drive to wherever it’s most needed.

Of all the systems, probably the most effective is the third differential arrangement. This sends drive permanently to all wheels, contrasting with, say, a multi-plate clutch system that operates as a front-drive only until the onset of wheelspin, when the back wheels will be brought progressively into play.

Because there is a delay in directing additional traction to help out the spinning wheels, such a system will tend to be less smooth-acting than one with all wheels driving at all times.

Then again, a constant all-wheel drive will tend to wear tyres out more quickly, while also consuming more fuel due to friction losses within the system.

Balancing the positives and negatives, and acknowledging the need to control development costs, is a delicate act often dictated by the amount of readily available technology - and hardware.

Mitsubishi, for example, picked up the three-differential arrangement used in its Lancer rally cars and adapted it to create an effective AWD system for the Magna. The systems used by Audi depend on the model: The transverse-engined TT quattro, for example, uses a multi-plate clutch system where the longitudinally engined A4 uses three differentials.

Volvo’s first foray into AWD was with its Cross Country V70 wagon, which relayed motive power from the transverse-mounted five-cylinder engine to the rear wheels via a multi-plate clutch. This system has also been adopted by the new XC90 soft-roader as well as the S60 AWD.

It is in the latter that the Ford-owned Swedish company reveals the directions its sedan cars may head in the future. The S60 AWD is not quite a tarmac-clenching supercar – it offers only a conservative 154kW – but then again it’s much more of a driver’s car than a regular S60.

It is definitely the Volvo to choose for a quick blast along a winding country road, or a night out in the rain.

The AWD system may not be full-time, but the transition from two-wheel drive is generally seamless - unless the car is asked to accelerate forcefully from a standing start, in which case the front wheels will emit a brief squeak before the rear-end has a chance to kick in.

Elsewhere, the system functions invisibly, only impinging on the driver’s awareness in the way it helps the car stay on line, and continue to accelerate cleanly when the road happens to get tight and slippery. There’s no levers or buttons to push, and no sounds or transmitted sensations to tell you how much is actually going on.

What is going on is a complex interchange between sensors detecting speed variations in the front and rear driveshafts. These signal the wet multi-plate Haldex clutch whether or not it should be engaged progressively to send drive through to the rear wheels.

So the S60 AWD is able to make full use of its 154kW, adding an unmistakable sense of security and maintaining grip where it would be unimaginable in a regular front-drive car. Perhaps the only downside is the typically Volvo suspension that can be felt bumping and crashing without too much provocation from the road surface.

The AWD S60 is also helped along by Volvo’s TRACS traction control system operating on the brakes to control a slipping wheel that, because of the AWD system, is not particularly prone to slipping anyway.

What it doesn’t get, however, is Volvo’s electronic stability control system which, on two-wheel drive S60s, helps counter tendencies to run wide in understeer, or lurch into a tail-out oversteer. This is undoubtedly due to the two different technologies – AWD and electronic stability control - not talking to each other.

Perhaps for the same reasons, the all-disc, four-channel ABS braking system does not incorporate the brake assist function that is also standard on other S60s.

And don’t expect your new Volvo S60 AWD to proudly announce its technological prowess: The presence of all-wheel drive is revealed with about as much discretion as you could possibly imagine – just a small badge on the boot and a set of special, 7.5 x 17-inch "Amalthea" alloy wheels running 225/45 tyres.

It’s essentially an S60 2.4T with a $2000-extra all-wheel drive system. This means multi-adjustable but manually controlled leather seats, climate-control air-conditioning, 60-40 split-folding rear seat, cruise control, trip computer and an eight-speaker sound system with single-CD player.

It differs from the 2.5T, in terms of interior presentation, via brushed aluminium highlights on the doors and glovebox.

If you want the extra safety margins, and enjoy a bit of a fling occasionally, the AWD S60 is a very worthwhile investment over a regular 2.5T.

The all-wheel system virtually substitutes for stability control, delivering not-dissimilar results via an electronically dependent but quite different control philosophy that makes it a driver’s car, not merely a safe one.