3PMSF vs M+S
Two markings on a tire's sidewall claim winter ability. They are not equivalent.
M+S (Mud and Snow)
M+S is a geometric definition: a tire qualifies if its tread has a certain proportion of void space and groove width. No performance test is involved. Almost every all-season tire sold in North America carries M+S, including tires that perform poorly on snow.
3PMSF (Three-Peak Mountain Snowflake)
The severe-snow symbol is earned by passing ASTM F1805, a standardized acceleration traction test on medium-packed snow, with results at least 10% better than a reference tire. It is the only certified winter-performance marking on a tire. All dedicated winter tires carry it, and a growing number of all-weather and all-terrain tires do too.
What 3PMSF does not test
The test measures acceleration traction on snow. It says nothing about braking on snow, ice grip, or cold-weather handling, where a true winter tire with a softer compound still has a large advantage. An all-weather tire with 3PMSF is a strong compromise for one-set-year-round drivers in moderate winter climates; it is not a winter tire.
How we score it
3PMSF counts for 10% of a tire's score in categories where some tires carry it. In summer-tire categories, where none do, the component is dropped and the rest of the formula rescales. See the formula and the best all-season tires for snow.