I think the better choice would be the Michelin X-Ice Xi2. The Bridgestone Blizzak WS-60 uses a multicell compound that is fantastic on ice, but that compound only runs through the first 55% of the tire, because the Blizzak compound doesn't have the necessary stiffness to make up the whole tire. After that, it's just a regular winter tire compound, which will not perform as well as the Xi2 will for its full life. Tires that are good on ice work by sucking up the thin layer of water on top of the ice - that's how you get traction. Multicell compounds do this best; apart form multicell tires, the Xi2 is the best choice for this, because it has lots of tiny little tubes designed to pump away the water from the surface of the ice.
I would actually recommend another tire for ice performance (the most important aspect of winter tire performance for me): the Yokohama Ice Guard IG20 (or for light trucks and SUVs the Geolandar I/T G072). It's got a multicell compound, but they solved the problem of tire stiffness by adding billions of tiny, semi-rigid bubbles throughout the tire, so the multicell compound makes up the whole tire, meaning that you get top-notch ice traction for the whole life of the tire. I think that the Yokohama Ice Guard and Geolandar are the best choice for winter tires, followed by the X-Ice Xi2. If Bridgestone manage to make a Blizzak with multicell compound through the whole tire in the next generation, it will be right back in contention.
It's worth noting that the Xi2 is currently ranked as the Best Winter Tire on the Consumer Search website, which aggregates results from a variety of sources, including a bunch of tough Scandinavian tests. It edged out the Blizzak in tests for the Tire Rack website. It's not quite as highly ranked by the Automobile Protection Association as the Yokohama and Blizzak tires (four stars versus five stars, but again, they're looking at the performance of the first 55% of the Blizzak, which is the deal breaker for me).
Here excerpts from are a couple of really good writeups on winter tires from the Toronto Star's John Mahler that will help to explain things:
ON THE YOKOHAMA ICE GUARD IG20:
The problem in winter driving is that there is almost always a film of water between the tire and the snow or ice.
The film of water is created by the weight of the car pushing on and compressing the snow or ice. The resultant film acts as a lubricant.
The next issue to solve was at what temperature was this phenomenon at its worst. There are two temperature ranges where this mini-aquaplaning occurs.
The first is when the temperature is between -6C to 0C. Here conditions are perfect for pressure from the tire to create water. The second situation is when ambient temperatures are above freezing and road ice is melting on its own.
The answer: a water-absorbing tire compound will work best. Multicell compounds have been around for a few years. These are compounds with little cavities in the rubber tread. As the tire rotated, new cavities were exposed, water could temporarily retreat into the hole and better rubber to road contact was possible.
Both the Bridgestone Blizzak and last year's Yokohama Ice Guard IG10 used that principle.
The problem is that all that porosity in the rubber made for a very sloppy drive on pavement.
The rubber was just not rigid enough to make emergency manoeuvres with confidence. The Bridgestone is only multicelled for the first 55 per cent of its tread life.
Yokohama looked to solve all of these problems with its new Ice Guard IG20, and it has succeeded, big time. The first brainwave was to use hard, hollow resin micro bubbles in the tread.
Dispersed like little beads throughout the tread, the bubbles allow the tire to remain rigid for more assuring grip in corners and under braking.
When the come in contact with the road, they pop open and suck in the water much like a suction cup. It is sort of like popping the bubbles in bubble wrap.
These little guys are typically 0.25 mm, which is very small to you and I, but looks like a huge cave to a 10-micron-thick water droplet.
After determining just how many of these resin pop toys could be used in a tire, Yoko went for the hat trick of water absorption via carbon flakes.
These flakes were shaped into heavily layered "beehives" measuring a giant 0.5mm. Capillary action draws road water up into these layers. As the tire rotates, water is expelled.
In total the average IG20 tire has about 2.5 billion of these hard micro bubbles and 1 billion carbon deposits.
To top all this, the Yoko IG20's tread pattern uses other elements to help manage winter roads. Four wide, straight grooves around the circumference of the tire help evacuate snow and water and contribute to straight-line stability.
Slush grooves run out to the shoulder of the tires to help drain wet snow and slush.
Driving pre-production IG20s last winter proved to me that the lab theory translated well where the rubber meets the ice.
In back-to-back comparisons with the new Ice Guard IG20, Goodyear UltraGrip Ice, Bridgestone Blizzak WS-50 and the Michelin Alpin, the new Ice Guard aced every test.
ON THE MICHELIN X-ICE Xi2:
Michelin has finally created a tire that uses air spaces in the rubber to act as little suction devices to improve ice grip. Michelin calls its design "micro-pump technology." Bridgestone pioneered this kind of grip enhancement with its Blizzak brand, and Yokohama continued in this direction with the IG20 Ice Guard.
Michelin has not entirely gone the route of the other two, which randomly have air pockets throughout the tread rubber. Michelin has added little tubes in a well-planned mixture through the tires' heavily siped pattern. The result is amazing stopping grip on ice superior to the X-Ice.
Ice is slippery because when we step on it or a car drives on it, the weight causes a thin film of water to be released. The water acts as a lubricant to increase the slip and slide of whatever caused the pressure.
Michelin combines the round micro-pumps with a new tread block heavily siped and made of a new rubber compound called FleX-Ice technology into its tread design.
It works simply. The leading edge of the tread block pushes most of the water out of the way in to the bigger grooves; the micro pumps absorb the remaining water; the sipes have better grip on the now-mostly-dry ice surface and, as the car moves forward, the pumps expel the water to be ready for the next contact.
It is an elegant solution to ice grip. On dry roads, the tire retains enough firmness in the tread to resist that dreaded "winter tire squirm."
The X-Ice Xi2 gets the "Green X" rating from Michelin, which means the rubber it uses is part of a line of tires that has lower rolling resistance and lower fuel consumption compared to a regular rubber. Michelin claims that if the world's vehicles were equipped with Green X tires, carbon dioxide emissions would be cut by 72.6 million tonnes.
Michelin claims its new tire will last 75 per cent longer than its main rival. The unnamed rival, I suspect, is the Bridgestone Blizzak. And that vast difference in wear rate would be based on the fact the Blizzak is a multicell compound for only 55 per cent of its tread depth. The remaining 45 per cent of the tire is a standard winter compound.
