Change your habits, change your tyres

I could think of no better way to start than with the question that opened the day: “Would you go to the snow in flip-flops?” The campaign’s slogan could hardly be clearer in making drivers aware of the need to adapt the vehicle to the adverse weather conditions we experience in our country, by fitting winter tyres, which, as we will see, are not only for driving on snow.

If the question caught your attention and you think we have lost our minds, think carefully about the answer and then apply it to your vehicle. You will understand that road conditions change with the seasons and that owners use the same tyres all year round. And winter tyres, besides performing excellently on snowy roads, also offer better performance than summer tyres when temperatures drop below 7ºC, whether on dry or wet surfaces. But let’s take it step by step.

Not just for snow

A very common mistake is to associate winter tyres only with extreme snow or ice conditions, but that is not the reality. The high silica content, together with other compounds in which rubber predominates, allows a much more effective performance on different road conditions during the winter months.

So it does not need to be snowing to appreciate the virtues of this type of tyre: in dry, rainy and even muddy conditions, as long as the temperature is 7ºC or below, grip will be much greater. In most of our geography, the average temperature in the coldest months is below this threshold, especially in the north of the country.

The main reason for this difference in behaviour is that the surface of a summer tyre hardens at low temperatures, preventing optimal contact with the road, and it can even lose contact and grip. The compound used in winter tyres prevents this stiffening.

In addition, the tread pattern has more widely spaced and deeper grooves to evacuate water more effectively and thus improve traction. This tread pattern also contains a large number of sipes that allow greater grip on snowy, wet and icy surfaces, thereby reducing the risk of losing grip and skidding.

First steps towards a common goal

Awareness. This is the clear objective set by the Tyre Manufacturers’ Committee, made up of the five major tyre brands: Bridgestone, Continental, Goodyear, Michelin and Pirelli, to promote the use of winter tyres in our country.

Over the last 2-3 years we have started to hear about winter tyres in our country, but not so long ago they were little known owing to the lack of awareness on the part of public administrations and the media. We do not have to look very far to see how, in certain neighbouring countries, their use is not only encouraged but driving with winter tyres is mandatory in conditions and seasons that require it.

The official designation for identifying them is a pictogram of a mountain with three peaks and a snowflake symbol. This pictogram appears on the tyre sidewall alongside the size and speed rating and, in some cases, alongside the letters M+S (Mud+Snow).

As the chart shows, the fundamental difference between winter and summer tyres, in terms of vehicle behaviour, lies in braking. Let us not forget that in an emergency, emergency braking activates the vehicle’s safety systems such as ABS and ESP, but they are not enough if there is no grip.

And taking this last point further, we cannot fail to mention the false myth that a four-wheel-drive vehicle does not need chains (and therefore winter tyres). Indeed, driving power to all four wheels allows the vehicle to move forward more easily, which is especially noticeable on uphill climbs. But when going downhill, we do not need any kind of traction, we need grip, so it is precisely in this case that winter tyres are most needed, even on vehicles with all-wheel drive.

The test track

All the theory is very well, but practice allows us to see for ourselves that winter tyres

perform far better in rain, snow or ice. The difference is less noticeable in dry conditions, but it does exist.

The test track was a polished cement surface with a grip/friction coefficient similar to rain on a dry surface, and which resembled a snow-covered surface when watered down, as was our case. It is also worth noting that to tell apart a car fitted with one set of tyres or the other, the photos show that on the front wing there is a scarf for winter tyres and a sun for summer ones.

The four dynamic tests replicated the real conditions we may encounter when driving on a road. First, the emergency braking on a bend over a slippery surface (snow): despite the action of ABS and ESP, we could see that with summer tyres the trajectory was almost straight, while with winter tyres the curve was almost perfect.

But where we could see the difference most clearly was in cornering at low speed (around 25-30 km/h), where the summer tyre tended to slide and leave its line at the slightest turn of the wheel, whereas it held its line when cornering with winter tyres.

The chart in the previous section was confirmed in the emergency braking on a wet surface. Both cars reached the same point at a speed of around 50 km/h, and the distance needed to stop completely with summer tyres was nearly 5 metres, roughly the length of a car.

The hill start also showed the huge difference in grip between one tyre and the other. While the traction system barely acted with the winter tyre (left, red car), with the summer tyre (right, blue car) it was really difficult to move even a metre. The photograph that accompanies these lines compares the rotational speed of the summer tyre’s wheels with that of the winter tyre under the same conditions, clearly showing that the summer tyre spins while the winter tyre does not.

When to change tyres?

The Committee recommends changing tyres when we move the clocks forward or back, in line with summer or winter time. So, in early November we can fit winter tyres, and remove them in the last days of March.

It should not be seen as an expense but as an investment, since you will extend the life of your summer tyres and, above all, gain in safety. Awareness is also essential: just as we consider fuel consumption, servicing or maintenance when buying a vehicle, we should include another item in the budget for changing tyres.

Increasingly, workshops offer their customers a storage service for tyres that are not fitted, to encourage their use and to keep the problems of acquiring winter tyres and investing in safety to a minimum.