Let’s just start with the big takeaway: as a general rule, if you drive someplace where the temperature falls below 45 degrees Fahrenheit (seven degrees Centigrade) with any regularity in the winter, you should put winter tires on your car.

Modern cars pack in so much safety technology—traction control, all-wheel drive, anti-lock brakes, and all the rest—that it’s easy to forget only one thing is truly keeping you from plowing into a guard rail or the car in front of you: a four-inch-by-four-inch bit of rubber called a “contact patch,” essentially the small bit of the tire that’s in contact with the road at a given time.

The grip provided by your tires makes everything happen in a car, from accelerating to braking to turning. Increase the grip, and you can do all of those things better. Decrease the grip, and you’ll end up using much more pavement than you planned—that is, if you can stop at all.