ZCanadian

So, about that R-compound rubber, see this From TireRack.com:


Whether you blame it on climate change, a polar vortex or what seems to be the beginning of the next ice age, there's no doubt recent weather patterns have exposed many drivers to freezing temperatures and wintery driving conditions. In anticipation of the next time Mother Nature extends her cold reach, drivers with vehicles equipped with summer performance tires need to know those tires are not designed for near- or below-freezing temperatures on clear roads, nor in slush, snow and ice.

When faced with near- and below-freezing temperatures, drivers should leave their summer performance tire-equipped vehicle at home and drive a vehicle equipped with all-season or winter tires.

Summer performance tires feature tread compounds engineered to provide traction in warm to hot ambient temperatures. They were never intended to experience near- and below-freezing temperatures, nor the wintry driving conditions that often accompany them.

As ambient temperatures get colder, typically in the 40-45° Fahrenheit range, summer performance tires lose a noticeable percentage of traction as their tread compound rubber properties change from a pliable elastic to inflexible plastic. The tire industry uses the term "glass transition" to describe the temperature where a summer performance tire's grip/slip performance changes dramatically. This means the summer performance tires that provide predictable traction in warm to hot conditions will be found to be very challenging to drive in cold to freezing temperatures. This is especially true when the tires first begin to be driven or if the driver aggressively applies gas pedal pressure with today's turbocharged fours or high-torque sixes and eights. Fortunately, glass transition is a reversible condition that allows the tires' normal traction to return as the ambient temperatures climb.

If ambient temperatures drop to near- or below-freezing, driving or rolling a vehicle equipped with summer performance tires risks the possibility of tread compound cracking. Tread compound cracking is a permanent condition that requires the tires to be replaced. The other condition that can be caused by running summer performance tires in cold temperatures is the possibility of chipping away the edges of the tread blocks.

Since both of these conditions only occur as the result of what's considered improper use or storage, they are not typically covered by the manufacturer's warranty.

Tire Tech - Performance Tires in Cold Weather