I drove in 25* this AM. I'd not recommend it much as at that temp the tires are so cold it's almost like driving in cold rain. I plan to move to snow tires soon. I don't think really under high 30's, is recommended.
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.