Although capable in their own way, all-season tires present their fair share of disadvantages, especially when it’s extremely snowy or icy. When it comes to traction, and distinguishing itself from the all-season variety – without a dedicated winter tire – the all-weather tire is a step up, typically displaying the 3PMSF (three-peaked mountain snowflake) symbol on its sidewall. Unlike the typical M+S script you see in most all-seasons, which is nothing more than a manufacturer-assigned label based on tread geometry, 3PMSF is a performance-based rating. To receive the rating, tires must pass a standardized test (ASTM F1805) set by the American Society for Testing and Materials.
For a tire to wear the 3PMSF symbol, it must provide at least 12% better acceleration traction than the standard reference test tire (SRTT). It used to be a P195/75 R14 tire (and only required a 10% minimum traction limit) but is now a P225/60 R16 tyre, according to the latest ASTM F2493 standard.
according to this research paper On winter traction performance, ASTM requires several parameters to be met before testing can begin, including preparing the surface and establishing the shear strength of the ice using a CTI penetrometer. Since a medium-packed snow surface is chosen, the ambient air temperature cannot exceed 38 degrees Fahrenheit, and the snow surface temperature must fall between 5 degrees and 25 degrees Fahrenheit. The test tire is then mounted on a special truck and rotated to evaluate its traction coefficient and, consequently, its tractive performance relative to the reference tire.
However, according to the test tire rackBraking or cornering don’t factor in, which is probably why testers found that some all-season tires labeled 3PMSF performed better in the real world than some other all-season tires.
Understanding the Latest Ice Grip Ratings
Where these all-season tires struggle for grip, proper winter/snow tires excel. In addition to the 3PMSF pictograph, some winter tires have another sidewall marking (a snowy mountain), known as the Ice Grip symbol, which requires compliance with the standardized braking test (ISO 19447:2021) set by the International Organization for Standardization.
You may have noticed the Ice Grip symbol on the Nokian Hakkapeliitta R5, which is one of Consumer Reports’ top picks when it comes to winter tires. To have that symbol printed on the sidewall, the tire has to undergo several rounds of brake tests on a flat, polished snow surface and provide a minimum of 18% better grip than the reference tire (according to ASTM F2493). according to car and driverThe snowy test bed is properly prepared to ensure that the surface temperature is between 5 degrees and 23 degrees Fahrenheit and the air temperature (measured 3 feet above the surface) is between 5 degrees and 39 degrees Fahrenheit, with no snowfall or rain.
A test vehicle with ABS that supports multiple wheel sizes is selected. Test tires are inflated according to the manufacturer’s recommendations, after which they are broken in by driving on dry pavement for 62 miles. Once everything is in order, the actual testing begins, which involves a series of braking runs over three different test cycles, during which the tire’s grip after coming to a complete stop from speeds of 12 to 15 mph is evaluated. As a fairly new addition to the tire grip/safety landscape, the Ice Grip rating will help consumers clearly differentiate between dedicated winter tires that stop well on snow and other tires carrying the 3PMSF symbol, which merely certifies the tire’s snow-traction capabilities.
