What Car? Q&A - Which car is best in slippery weather?

Q: We live in the Granada area of Spain, which is subject to snow and ice, and want to change my wife's car. We have a shortlist of the BMW 320d Tourer and the Jaguar X-Type Estate. In your reviews, little is made of the safety aspect of four-wheel-drive in the Jaguar, and I don't know much about the traction control aspect of the BMW. Can you cast your vote?
Alan Stafford

A: The four-wheel-drive system available on the Jaguar is called 'Traction 4' and is only available on 2.5- and 3.0-litre V6 models. The system automatically senses the difference in speed between the front and rear wheels, searching for the optimum balance and traction by varying the distribution of power between the front and rear wheels.

Such a system would certainly prove useful in icy conditions. For example, if the rear wheels started to slip, up to 60% of the engine's power could be transferred to the front wheels to counteract it.

The BMW is rear-wheel-drive. However, it has numerous traction devices: Dynamic Brake Control (DBC), Cornering Brake Control (CBC), Dynamic Stability Control (DSC) as well as Dynamic Traction Control (DTC).

These electronic aids act to assist the driver if he or she accelerates too hard, corners too quickly or brakes too sharply.

However, all the electronic aids in the world can't rewrite the rules of physics. These devices make the most of the available traction, but don't provide any extra grip. By distributing power to all four wheels, the X-type will have better traction than a rear-wheel-drive car, because each wheel has only half as much work to do.

It is important not to confuse traction with cornering grip. Traction is the car's ability to put its power to the road surface, while grip is its adhesion to that road surface. Four-wheel-drive improves traction. However, it does not improve cornering grip.

Remember, too, that in much of Continental Europe, drivers fit winter tyres, which dramatically improve traction and grip in snowy conditions.

If you want the safest, most secure drive, we'd go for the four-wheel-drive X-type, and fit snow tyres in the winter months.