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09/05/2011
Winter tyre safety on trial

Tyres in control

 

An account of a day of tests in the shadow of the Matterhorn organized by Assogomma and Federpneus to draw the attention of the media, the institutions and the police to the difference between winter and summer tyres through personal experience. 

By Mino de Rigo

Various vehicles were available for the trials, from Alfa Romeo Giuliettas to Jaguar XKR supercars to Mercedes GLK SUVs (front-wheel drive, rear drive, and four-wheel drive, respectively), the Toyota Auris and the Peugeot 5008.

 

For six years now it has been the custom for the Assogomma and Federpneus winter holiday week to coincide with the organization of a broad series of dynamic tests centred on winter tyres and on a wide-ranging comparison with their summer counterparts. The aim was to give practical demonstrations of the importance of using the former during the winter for your own safety and that of others. This year's appointment in a snow-covered Cervinia in the middle of February was with the manufacturing members of Assogomma (Bridgestone, Continental, Goodyear, Dunlop, Marangoni, Michelin, Pirelli, Yokohama). The tests were created as part of the "Tyres in control" campaign and had a considerable number of participants from the police forces and institutions, and the subsequent presence of numerous journalists from the general and specialist press. "The main purpose" - stated Assogomma director Fabio Bertolotti - "is to give a practical demonstration that will emphasize the superiority of winter tyres during the coldest months, regardless of the type of vehicle, drive and engine, or of road conditions and therefore even with no snow". The characteristics of winter tyre performance were tested not only on a flat snow-covered circuit and on the track of an ice drome borrowed for the occasion from the karts, but also just outside the town in sleet and on a wet road, which was duly closed to traffic, with straight uphill and downhill stretches and hairpin bends. 

 

Vehicles of different type, drive and engine
Various vehicles were available for the trials, from Alfa Romeo Giuliettas to Jaguar XKR supercars to Mercedes GLK SUVs (front-wheel drive, rear drive, and four-wheel drive, respectively), the Toyota Auris and the Peugeot 5008; the comparisons were made by driving identical vehicles fitted with winter tyres, their summer counterparts, and mixed tyres, with winter tyres on the drive axle of two-wheel drive vehicles. Vans were also included in the tests at Cervinia.
Mercedes Sprinter school buses were tested on a snow-covered road and had to make an emergency swerve at 45 km/h and then at 50: the first manoeuvre was successful for both drivers, the second was not; steering was lost in the bus with the summer tyres and it veered dangerously off course. Then it was the turn of two ambulances (vehicles that weigh 2,200 kg), which drove along a straight road at 50 km/h and then made an emergency stop: the vehicle with the winter tyres came to a stop in 21.5 metres; its twin with summer tyres took over 10 metres more.


Behind the wheel for a direct comparison
The result was in line with the experience in the other vehicles and with Assogomma data: for an average-size vehicle fitted with winter tyres travelling at 40 km/h on compacted snow and in an ambient temperature close to zero, braking distance can be shortened by up to 50%; at 90 km/h on wet roads, the braking distance can be decreased by up to 15% compared to a vehicle fitted with summer tyres. At last it was time to test the supersporty XKRs. We had to drive several times at increasing speeds on a track that simulated entering and driving on a roundabout in order to evaluate the difference between the vehicle fitted with winter tyres and another of the same kind fitted with a mixed set; parked on the flat in the snow, the third car fitted with summer tyres was out of action. Thanks to the long-wheelbase, generous section width (275/35 R19) and rear-wheel drive, there was a distinct difference in behaviour between the two vehicles which both had active electronic controls. In the first, we were able to reach a maximum of 40 km/h before it became more difficult to handle and moved towards the outside, but in the second, at 25 km/h it already began to show obvious signs of understeer and went off course. This demonstrated that a complete set of winter tyres is more than just good sense. The test in the Giuliettas was impressive. Fitted with three sets (winter, summer and mixed), they did a short slalom in the snow, an emergency stop and swerve, as if to avoid an unexpected obstacle.

 

Mixed tyres
The Giulietta with the winter tyres easily negotiated the cones at over 30 km/h and stayed on course even after "panic" braking at 45 km/h. Then we tried the Giulietta with the winter tyres only on the front drive: at the start there was a reassuring feeling of being in charge of the vehicle, and initially there was no lack of traction or steering. But after a few twists and turns, suddenly it went into a sideslip and the rear wheels began to lose traction without any warning.
Conscious of their inadequacy, we were more prudent when we tried the car with the summer tyres, but it showed signs of losing grip (the same on all wheels) and going off course was predictable.
"As far as we are concerned" - the director of Assogomma emphasized - "we recommend a solution that is unequivocal and optimal: always use four identical winter tyres".
The test in the Mercedes GLK 220 CDI 4Matic (four-wheel drive and automatic shift) was very instructive. First we did the stopping and starting test on a short slope with an incline of about 30°, and then we followed a marked route with a short hairpin bend and came back down the same slope.

 

KO for 4x4 SUVs with summer tyres
We did the first part of the ascent without any problem in the car with the summer tyres; but after we stopped, the GLK couldn't get started again and began to do some remarkable side slipping. We had to put it in neutral, keep our foot on the brake and let the car slide backwards to a point that was less steep and it could get going again. Going back down at just over 30 km/h there was no grip either and the SUV was totally unable to stop. The data testified to an extremely risky slide of 38 metres compared to the 12 the SUV with winter tyres needed to stop, which, by the way, took us up the slope without any hesitation. The next test was on an uphill and downhill stretch of road that was part asphalt and part snow. Handling and braking the Toyota Auris and the Peugeot 5008 fitted with summer tyres and chains paled in comparison with that of their sisters fitted with winter tyres. The carousel of winter-summer comparisons concluded at the ice drome with two empty Fiat Ducatos and then with 400 kg loads in the back. Telemetry testified that the former had higher deceleration peaks compared to the latter, which was thanks to grip given by the compound and sipes, and much shorter stopping distances that were emphasized by the load configuration. The van with summer tyres did not do more than 30 km/h, but the one with winter tyres completed the circuit without any obvious loss of grip at around 40 km/h: a safety test that was complete and convincingly successful.

 

• Non-stop growth for winter tyres


The winter tyre market continues to grow at a fast pace. According to Assogomma, in two years sales have more than doubled from about 3.2 million units in the 2008-2009 season to almost 6.5 for the winter that has just ended: "Compared to the previous year" - added Assogomma director Fabio Bertolotti - "sell-out has had extraordinary growth and already stands at 4.5 million units. And the margins for development are still particularly wide".

 

 

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