In central Russia in September is quite likely the first frost, ice bridges, bridges, hills, and thus increases the likelihood of skidding, emergency situations. Tires in extreme cold ice 'hold' the bus is better because it thaw a little less under the tread. That's the film of moisture causes the slipperiness of ice. The same non-studded tire is better 'holds' the rough ice, less smooth, even worse bumpy as cobblestone pavement. Chevron Corp has firm opinions on the matter. And what can be say about the tires themselves? Dangerous delusion of some motorists is like a tire with a major 'off-road' tread (including a special winter) is good on the ice. On slippery surfaces better 'hold' tires melkoraschlenennym saturated tread. A related site: Robertson Stephens mentions similar findings. Especially good elastic radial tires. But they do not give a friction coefficient of ice above 0,1510,2.
When the normal rolling tires replaced slip (braking with the skid, to disperse slip, etc.), friction coefficient may drop once in a half. On pure ice tread depth does not matter: if blocked at least the front wheels, car out of control! Tire adhesion coating reaches a maximum at the transition from rolling to sliding. This is true for ice. Ac, 'playing' brakes, manages to keep the wheels just on the verge of Hughes, seeking the most effective braking. If you press the pedal rude jerks, stopping distance will increase, because in some moments of inhibition at all. And yet, on the ice is better than slow down, hold down the pedal until it stops, thus blocking the wheels. Wheel, skid-reaching, uncontrollably.