Swapping summer tires for snow tires was something Grandpa did every fall. Science says Grandpa was right.

Repeated testing by multiple independent organizations in North America and Europe has shown that winter tires will out-perform most all-season tires when the temperature drops below 40 degrees F. At those temperatures, winter tires start to gain an advantage in grip and handling on dry pavement — and are significantly better when the weather turns nasty.

All-season tires are designed with tread patterns that offer long wear and acceptable traction in a variety of conditions, including light snow and slush. They’re fine for places that see only an occasional dusting of snow or limited days of frigid weather, which is why most new cars sold in North America are outfitted with them. But in most cases, all-season tires are actually a compromise between convenience and cold-weather performance.

Below 40 degrees, the rubber in most all-season tires will start to stiffen and become less pliable, compromising both grip and handling. Cars will be more susceptible to skids and will need substantially more distance to brake safely.

Winter tires: Not just for snow

Winter tires have two major differences that set them apart from their fair-weather peers. First, they’re made with rubber compounds formulated to remain flexible and grippy even down to -25 degrees F. That flexibility is enhanced by a design that incorporates multiple thin grooves in the tread, called sipes. These spread slightly under pressure to get more rubber on the road, increasing traction on ice, snow and wet pavement.

On wet, slushy roads, the siping can help a winter tire brake 20 percent shorter than an all-season tire, which could mean the difference between a close call and a crumpled bumper.

In severe cold weather, the advantages of modern winter tires really start to stand out. The Transportation Research Center at the University of Fairbanks, Alaska —where the official school mascot is a polar bear named Nanook — ran a series of tests in temperatures averaging a balmy 10 degrees. Researchers found that winter tires stopped faster and climbed snowy hills significantly better than all-season tires and, in a surprising twist, performed about as well as studded tires, the traditional choice for extreme cold-weather driving.

Studded tires had a slight edge in icy conditions, as expected, but researchers discovered that it was a short-lived advantage: All three types of tires were re-tested after 1,000 miles and the winter tires performed as well or better than the studded tires and all-seasons.

In one of the most convincing tests, teams of Canadian researchers from the Automobile Protection Association, Transport Canada and the Rubber Association of Canada compared all-seasons with winter tires on a variety of vehicles in simulations that mimicked real-world driving scenarios. The result: on every car, from compact sedans to large SUVS, winter tires offered as much as 50 percent better traction than all-season tires and allowed drivers to stop faster and turn safer.

Those are the major reasons why Quebec now requires all cars registered in the province use winter tires from December 15 to March 15.

If you’re thinking about a set of winter tires:

  • Look for the mountain snowflake symbol. It identifies winter tires that beat or exceed winter tire snow traction standards set by the American Society for Testing and Materials (ASTM).
  • Don’t be fooled by a “M+S” symbol. It’s an older designation that indicates a tire with a tread designed for mud and snow, but the tire doesn’t have the special rubber compounds and siping that meet the tougher testing standards for a winter tire.
  • Install winter tires in complete sets of four, especially on all-wheel drive vehicles, to avoid inconsistencies in traction between the wheels. Too much of a difference in grip will negatively affect handling and the performance of a car’s traction-control systems.
  • If convenience is key and cost is no factor, consider looking into winter-rated all-season tires. These are made by a handful of manufactures, including the Finnish company Nokian.

Mike Saunders is a former Boston Globe writer who spends entirely too much time in his garage.