Three-peak mountain snowflake (3PMSF)

How to read it

The symbol is a mountain outline with three peaks, the middle one tallest, and a six-sided snowflake inside, at least 15 mm wide and 15 mm high. In the US, FMVSS 139 calls it the Alpine Symbol and lets a manufacturer mark it on a snow tire: one that reaches a traction index of at least 112 against the ASTM F2493 standard reference test tire in the ASTM F1805-20 snow traction test on medium pack snow. USTMA’s severe snow definition (TISB 37) uses the same test, with a minimum snow grip index of 1.12 against that 16-inch reference tire, or 1.10 against the older 14-inch one, and marks qualifying tires with the M and S letters plus the pictograph. Bridgestone’s glossary calls it the mountain snowflake pictograph.

Also searched as: 3PMSF, alpine symbol, severe snow symbol, snowflake on tire.

Mountain snowflake or M+S?

M+S describes the tread: under USTMA’s definition (TISB 10) it rests on slot sizes and the share of open space in the tread, with no snow test. The mountain snowflake needs a measured result on snow. Continental calls it a more stringent certification, and Bridgestone says tires with it have improved snow performance compared with tires meeting the all-season definition.

Where the symbol came from

The Tire and Rubber Association of Canada says the Canadian tire industry and TRAC led the creation of the ASTM F1805 test and the symbol, and that both have been used around the world since 1999.

Differences by country or standard

Canada’s Motor Vehicle Tire Safety Regulations define a winter tire by the same ASTM F1805 test (a traction index of at least 110 against the 14-inch reference tire, or 112 against the 16-inch one) and require the Alpine Symbol on at least one sidewall. In British Columbia, a tire with the symbol or with M+S counts as a legal winter tire on signed highways; the province notes that some makers mark both. In Europe, Continental’s guide to UN Regulation No. 117, which sets tyre limits for rolling resistance, sound and wet grip, describes 3PMSF tyres as those which have passed the snow test.

Look-alike: the ice grip symbol

USTMA’s TISB 56 describes a second pictograph for passenger tires designed for ice: a mountain with three icicles, the middle one longest, marked alongside M+S and the mountain snowflake. Its design comes from UN Regulation No. 117.