High speed fun in snow and ice

ROB MAETZIG
Last updated 13:57 22/08/2012
Taranaki Daily News Online

BMW claims its xDrive all-wheel drive system is the most sophisticated on the market. It gets tested out on snow and ice in the South Island.

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There was a serious side to the high speed fun in the snow and ice driving luxury BMWs in the Southern Alps.

High up in the snow overlooking the Cardrona Valley, BMW New Zealand technical guru Lance Roskilly explains why the German luxury marque's xDrive is the superior all-wheel drive system.

Almost every other modern-day AWD systems are controlled by viscous couplings that contain fluid that remains liquid when cool, and which has to be heated by friction caused by wheel slippage to become near-solid.

So a vehicle with a viscous coupling has to be experiencing slippage before its AWD system can become fully operational, Roskilly explains.

But not xDrive. Its torque transfer case has an electronically controlled clutch that uses numerous other vehicle inputs to react in mere fractions of a second.

It could even be said that xDrive thinks ahead, says the BMW man. Enter a fast bend, climb a hill at speed, drive over a different surface, threaten to move into oversteer or understeer situations, and the system will notice the change and immediately transfer drive torque to the axle with the best traction.

It all happens so quickly - within 200 milliseconds - that before the person behind the wheel even notices a change has taken place, the BMW's behaviour will have been stabilised.

But wait, there's more, says Roskilly.

Whereas other AWD systems can only transfer drive torque between the front and rear axles, xDrive can also transfer it from side to side. It does this by co- ordinating with the BMW's dynamic stability control and its subsidiary function, traction control.

That means, he adds, that even if only one wheel is on a surface on which it can get any decent sort of traction, that can be enough for a BMW with xDrive.

And to prove it all, we traipse outside and head to a steep slope where one side of a pathway is concrete, and the other side is pure ice.

The BMW people arrange for a person in a Japanese 4WD SUV to stop on the slope with its right wheels on the concrete, left wheels on the ice, then attempt to get started again. But it can't happen because the viscous coupling can't handle the requirement.

Then the same thing is attempted with a BMW X5, and this time the vehicle easily heads to the top of the slope. The BMW people try the same thing again, only this time with just one quarter of one tyre on the concrete.

Once again, the X5 with its xDrive simply pulls away. It's an impressive demonstration of just how good xDrive is.

So too is the rest of the day - which mostly involves high-speed fun on the snow and ice of the proving ground in what is known as the BMW Alpine xDrive Experience.

For most of each winter, the Southern Hemisphere Proving Ground is a top-secret facility where northern hemisphere car and tyre manufacturers use their summer months to conduct all sorts of winter testing.

But, come August, all of this testing is finished, which leaves a few weeks for a few luxury car companies to educate paying clients and guests on how to drive in icy conditions. This year BMW, Mercedes-Benz and Audi are all up there.

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It's huge fun, too.

Even right now, groups of BMW guests are being bussed up to the site to spend the day blasting over the snow in a selection of the marque's X1, X3 and X5 sports activity vehicles.

Drifting, slalom courses, braking on a massive sheet of ice, time trials, and opportunities for hot laps with the real experts are all part of each day's programme of activities.

But while there's the massive fun element, there's also a serious side to the xDrive Experience.

"BMW is renowned as having the world's fastest-acting all-wheel- drive system, but even with reassurance such as that, people should adjust their driving style to cope with ice and snow situations,' says the event's lead instructor Mike Eady.

"All too often, speed is the biggest factor which contributes to accidents, and the old adage proves true time and time again - it's vitally important to drive to the conditions.'

Important considerations to keep front of mind when driving on ice and snow are to turn on your lights, increase following distances, slow down, brake on the straight and take your time, he adds.

Making the most of the available traction is key to winter driving, says Mike Eady. ''Loss of traction can lead to wheelspin under acceleration, wheel lock under braking and sideways sliding while cornering. There are many automatic stability control systems which can control these actions to a limited extent, but there is no substitute for the correct technique.

''Investing in a vehicle with ABS is the single-most-effective method of increasing your safety in slippery conditions.

''Traction-control systems can control wheelspin, but bear in mind that these systems are reactive, which means you'll have to be in a certain amount of trouble before they will start to operate - it's much better to avoid the problems to start with.'

HOW TO DRIVE ON SNOW AND ICE:

Pull away and accelerate gently and progressively. In slippery conditions such as snow and ice, aggressive acceleration will almost certainly break traction at the driven wheels. The resulting wheelspin can lead to loss of steering control in a front wheel drive car, or an oversteer slide in a rear wheel drive. Both of these situations will prevent you from going in the direction you want and can be difficult to recover from.

If you do notice wheelspin (or the traction control systems fighting for grip), don't floor the throttle, instead back off the gas and then reapply smoothly.

Best practice is to keep engine revs low in order to maximise your grip in winter conditions. Keep a constant gentle throttle for best results. Most diesel engines will cruise along nicely in low gears without using any throttle.

Change up sooner rather than later, pull away in second gear if possible, and use the highest practical gear at all times. This reduces the torque at the driven wheels and will therefore reduce the chances of wheelspin - also a useful trick when trying to climb a slippery muddy hill. Keep gear changes as smooth as possible - it will be easy to spin the wheels in most gears when conditions are really bad.

Avoid any sudden driver inputs (such as steering, braking, acceleration or gear changes). You only have a finite level of grip available and you don't want to overload your tyres unnecessarily. Driving smoothly will conserve grip, and make you a safer driver.

Brake soon, and gently. Be prepared to ease off the brakes (if you do not have ABS fitted) in order to steer more effectively. Locked wheels cannot steer!

If you do have ABS, you'll be able to tell it has triggered by feeling a pulsing sensation through the brake pedal. If this has occurred do not 'pump' the brakes - rather keep a firm pressure on the pedal for maximum effectiveness. ABS is designed to help you steer as you're slowing down so use this to your advantage and avoid obstacles.

- Taranaki Daily News

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