Winter testing at new Bridgestone proving ground

With the increasing use of cold weather tyres across many European markets as a result of legislation, recent harsh winters, and increased product awareness, the development cycle for new models has reduced in length. The world’s biggest manufacturer, Bridgestone has responded to the increased interest in the segment – and the resultant quickening of technological improvements – by signing a long-term lease on its new Sweden Proving Ground (SPG), located in Vidsel in the north of the country under 100km from the polar circle, and an hour’s drive north of Lulea airport. Its representatives told tyrepress.com that the estimated new seasonal product cycle would now be “no more than two winters”, since the “life cycle of a winter tyre is getting shorter”.

In temperatures ranging between -25 and -36°C and with the ground blanketed in thick, powdery snow, the company showed tyrepress.com the new facilities the SPG offered, completing a number of demonstrations in Audi A3 Sportback 2.0 TDIs on its current model Blizzak LM-30 tyre in comparison with a prototype of what will become its replacement – the LM-32. For comparison, T&A also sampled the performance in the same conditions of the company’s recently launched A001 Weather Control all-season tyre, and some Turanza ER300 summer tyres.

The most direct comparison of the three tyres came in the safety test performed on a long, flat, white runway, and involving one sharp corner, a slalom and a straight-line braking test. The kindest thing that can be said of the performance of summer tyres on snow is that they are unresponsive. Attempting to slalom at anything above a snail’s pace resulted in catastrophe for the cones marking the route. Meanwhile, attempting to reduced the A3’s speed from 50kmh to a standstill was complicated by the inability to pick up speed quickly enough to reach the target by the braking point. Even at speeds lower than suggested, braking on snow at -31°C on the ER300 cannot be recommended.

Perhaps the most interesting subjective comparison of the day for T&A came in performing the same tests on the new A001 all-weather rubber. The tyre is designed as a “light winter tyre” according to Bridgestone representatives, and it is easy to see how this rubber can be applied to mild weather markets – Bridgestone uses the term “Oceanic” – such as the UK. With January temperatures often averaging between 5 and 10°C and July between 10 and 20°C. Markets such as the UK, Benelux and northern France and Germany are regarded as Bridgestone’s “optimum regions” for the tyre.

Using the A001 in temperatures firmly outside its optimum operating range, and on resolutely heavy, rather than light snow, T&A experienced a large performance gap between the all-weather compound and the ER300. The tyre enabled the A3 to reach the correct speed for the braking test, and while the stopping distance was quite a bit longer than the tyres designed actually to operate well on the snow, the car ground to a halt much quicker than when the test was run on ER300s. Not a single cone was hurt in the running of the slalom.

Comparing the LM-30 and the LM-32 prototype on the safety test was to see the incremental improvements premium brands often aim to achieve in all new tyre models. As you would expect, both were appreciably more stable than the ER300 and A001, allowing T&A to move and brake at far greater speed, while the braking test was completed without fuss. Playing the two tyres off against each other, the stability offered by the symmetrical pattern of the prototype against the asymmetric LM-30 allowed testers to achieve braking of 55-0kmh and acceleration of 15-55kmh in distances shorter by 1-3 metres. This was confirmed by the SPG’s objective testing devices on board the A3s.

All-weather the way to go in UK?

In terms of the UK market, this testing was very interesting. While the increases in winter tyre demand after 2009 in the market have been an encouraging sign that some drivers are waking up to the mobility advantages of different tyres in the winter months, it is easy to see how another mild winter such as the 2011/12 season could cool interest considerably. Judging by the improvements yielded by fitting all-weather rubber instead of the usual summer tyre that the vast majority of Britons continue to operate in winter, it seems that the compromise could increase safety during the temperate British seasons, while also removing the short term cost of purchasing – and changing onto – a second set of tyres. And on the odd particularly harsh winter day, meaning only a few degrees under freezing in the British climate, the indication is that these tyres would vastly improve the safety, and even the viability, of travelling the UK’s road networks.

Specifically, the A001 improves front-rear balance, and gives cars more stable cornering and strong traction in both wet and dry. On wet roads, its lens-shaped blocks allow smoother water evacuation with lower water turbulence, reducing the risk of hydroplaning. The pattern’s high-density siping helps the tyre grip on cold, frozen and snowy roads, increasing confidence in handling and braking. Bridgestone has also tuned the tread pattern for low noise and optimum road contact in all surface conditions. The tyre is M+S (Mud + Snow) marked and rated as a snow tyre in most markets where winter tyres are required by law. It is available in 11 popular small and compact sizes.

Andy Dingley, communications manager, Bridgestone Europe North Region made the point that the tyre could help address winter conditions the way UK drivers tend to use the product: “We feel that a balance must be struck where families can drive safely in all road conditions in the UK without breaking the bank, and Weather Control tyres could be that balance for many motorists.”

Objective testing facilities

Dingley and other Bridgestone representatives also said that the company was focused on providing “specific tyres for all conditions”, and while the A001 seems like a decent single-tyre compromise for Oceanic climates such as the UK’s, developing winter-specialist products for Europe remains a commitment; hence the investment in the SPG.

The proving ground has the space and facilities to give Bridgestone the capability to use objective winter tyre testing, the equivalent of that conducted at the company’s summer tyre proving ground in Aprilia, Italy. Objective testing measures vehicle movement quantitatively, enabling engineers to calculate the tyre grip force in contact with the frozen surface. The data provides the platform for much more precise tyre design. Bridgestone was keen to stress this in the prototype tyre’s case – the tyre is completely redesigned, with a new tread pattern and lighter construction, the latter of which should help reduce fuel consumption.

“Our investment in SPG provides Bridgestone engineers with the data-driven analysis they need for class-leading winter tyre development” explains Fernando Baldoni, general manager of Tire Research at Bridgestone Europe. Traditional winter testing has been largely based on “subjective” handling, supported by laboratory simulation, with drivers scoring tyres on a “feel” basis for steering, cornering and overall grip. Objective testing includes GPS-based and optical sensors on the car relay data on the vehicle dynamics, which are simultaneously compared to actual steering angle information.

“Bridgestone’s winter proving ground is more than an icy test track… it’s an engineering centre at the heart of winter tyre technology development” says Baldoni. The facility provides the company with an exclusive winter tyre testing facility for 14 to 17 weeks a year. The data from the ground provides the platform for much more precise tyre design – such as that found in the prototype LM-32.

Underlining its commitment to winter tyres Bridgestone will be a main partner at 34 Audi FIS Alpine Ski World Cup events in nine European countries – Austria, Finland, France, Germany, Italy, Slovenia, Norway, Sweden and Switzerland – during the 2011-2012 season. Associating its brand with winter sports gives the company access to a strong following and TV audience, in addition to accessing the prestige and performance messages of top level sport.