Winter is the harshest season for your vehicle and the most dangerous for you as a driver. Your car will be exposed to snow, ice, rain, slush, freezing temperatures, and road salt. On top of that, many of us will be driving thousands of miles over the Christmas holidays under unpredictable road conditions.
For your security, the single most important item is to use winter tires, (aka snow tires). No matter how carefully you drive, not using winter tires on snow, ice, or slush will increase your chance of spending some time in the car repair shop or worse.
Winter tires not only guarantee that you will be able to brake securely, but also that your car won’t loose grip accelerating or driving around corners.
All-season tires (those marked ‘M+S’ or ‘M&S’) are appropriate under most conditions. Just remember that these tires stiffen and loose grip under extremely low temperatures. If you have to drive under those conditions, remember to keep a longer security distance from the vehicle in front of you. However, if you are security minded, just change your summer tires before the first snow has fallen. They are clearly a little bit cheaper than having two sets of tires (for winter and for summer). However, I doubt that it represent a true saving. All-season tires wear more than normal summer tires and have less grip than normal winter tires. And in the case of an accident, the saving is definitely gone.
Some SUV drivers make the mistake of thinking that since they have large wheels with wide tires, they don’t need winter tires. Actually, only tires explicitly marked as winter tires (or all-season) are suitable for snow and ice. Otherwise, no matter how aggressive the profile of your tire may be, you will have to mount new tires on your vehicle. Winter tires are not only different in their profile, but also on the rubber they are made from.
And last but not least, don’t try to save a couple of bucks putting winter tires only on the traction wheels. Your car need the same kind of tires on all its wheels. If you mix tires with different attributes, your car may exhibit an unpredictable braking pattern, even if you have the most advances security features like ESP (Electronic stability control).