Tire buying guides

How are M+S and 3PMS calculated?

SimpleTire Graphic showing icons and location for M+S and 3PMS.
Last updated 10/14/2022 - Originally published 2/15/2021
Written by SimpleTire

Just as a group like Underwriters Laboratories performs testing and establishes safety standards for consumer products, winter tires are tested and graded for overall traction, braking performance, and handling. Tires that meet those standards are marked either with the M+S (Mud and Snow) stamp or 3PMS (a graphic of three mountain peaks and a snowflake) symbol, both of which represent industry standards. However, the testing processes and the traction they can deliver are quite different.

M+S deep dive

M+S Icon

What the M+S rating means

The tire industry realized they needed a better traction rating system in the ‘70s, as the clunky, old, heavy bias-ply “snow tires” from your dad’s old Buick were quickly becoming obsolete.

The M+S rating means that a tire has better mud/snow traction than a summer tire, but it doesn’t really tell the whole story. An M+S rated tire will have better traction on packed snow or mud, but the rating doesn’t reflect traction for wet, soupy mud, slush, ice, fresh snow or even cold, dry pavement.

That said, if your area doesn’t see more than an inch or two of snow most winters, an M+S rated tire can be a great year-round choice.

How M+S is calculated

Our industry’s standards are a little complex, so let’s simplify it a bit: for the M+S rating, 25 percent of a tire’s tread area has to be taken up by grooves to allow the tire to eject mud and snow, and always have a clear section of tire to dig in as the wheel turns.

Other computer-modeled, laboratory, and real-world testing methods come into consideration before a tire can be certified with the M+S designation. For instance, Toyo has developed artificial intelligence-based testing for winter traction that’s as reliable as any real-world testing. Other tire manufacturers like Continental, Michelin, Nitto, and Nokian all have specific tests for traction, cornering, acceleration, and braking performance on snow-, slush- or ice-covered pavement.

3PMS deep dive

3PMS Icon

What the 3PMS rating means

There are more stringent requirements for “severe snow service” tires and that’s what the 3PMS rating indicates. The tread formulation has a lot to do with this rating; in subfreezing temperatures, all season tires tend to stiffen up and lose traction, but a tire that’s 3PMS rated is designed to stay flexible in cold weather. That means an enhanced ability to dig in on snow and slush, like the difference between the hard rubber of a hockey puck which slides on the ice, and the soft rubber of a snow boot that flexes, conforms, and grips otherwise slippery surfaces.

How 3PMS is calculated

This is another one where the ratings are a little narrowly-defined. The 3MPS rating is determined by acceleration on medium-packed snow only, with no consideration for braking or cornering traction.You can think of all weather 3PMS tires as splitting the difference between all season tires and dedicated winter tires - and unlike winter tires, they don’t have to be changed when temperatures get above 40 degrees F.

We should probably mention that many light truck all terrain tires will have the 3PMS stamp on the sidewall too, although they’re not always ideal in heavy snow. Still, on a 4WD truck or SUV, all terrain tires with the 3PMS rating can be a great choice to get you through when things get rough.

It’s also worth noting here that there are provinces in Canada, as well as several far-north states in the US, that mandate 3PMS tires, during certain times of the year. If you’re living in one of those areas, it’d be worth your time to check if your tires comply with local mandates.

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