3PMSF vs. M+S: What the Snow Symbols on Tires Mean

Look closely at the sidewall of a tire and you will find small codes molded into the rubber. Two of them cause the most confusion every fall: the letters M+S and a tiny mountain with a snowflake inside it. They seem to say the same thing. They don’t. One describes how the tread is shaped. The other tells you the tire passed an actual snow test.

This guide explains what each mark stands for, what it does and doesn’t prove, which kinds of tires usually carry it, and how to find it before you buy. If you are still deciding whether you need winter tires at all, our comparison of winter tires vs. all-season tires covers that question. Here we stick to the symbols.

What M+S really means

M+S stands for “mud and snow.” You may also see it printed as M/S or a similar variation. The mark has been around for decades, and it is based on tread geometry: the pattern of grooves, slots and open space in the tread. It is not based on how the tire actually performs in snow.

Under the long-standing industry definition, an M+S tread needs slots or pockets along its edge that reach in toward the center, plus a minimum amount of open “void” space (about a quarter of the contact surface, measured from the mold). Those open channels give snow and mud somewhere to go, which helps the tread keep biting instead of packing up.

What M+S does not tell you matters just as much:

• No snow test is required. A tire can earn the letters on its tread design alone. Major tire makers say plainly that M+S is not a certified performance rating.
• It says nothing about the rubber. Winter grip depends heavily on a compound that stays soft in the cold. Michelin, for example, notes that all-season rubber begins to stiffen below about 45°F, and the M+S mark doesn’t tell cold-weather and warm-weather compounds apart.
• It isn’t a winter rating. Plenty of all-season, all-terrain and mud-terrain tires carry M+S. That makes the mark common, but it is not a sign the tire was designed for winter roads.

What the three-peak mountain snowflake means

The Three-Peak Mountain Snowflake, usually shortened to 3PMSF, shows a mountain outline with three peaks and a six-sided snowflake in the middle. The U.S. and Canadian tire industries have used it since 1999 so drivers would have a mark backed by a test, not just a tread shape.

To carry the symbol, a tire goes through a standardized traction test, known as ASTM F1805, on medium-packed snow. The test measures how well the tire grips while it pulls the vehicle forward, then compares the result to a standard reference test tire. The current U.S. federal definition, updated in 2022, calls for a score of at least 112 on a scale where today’s reference tire scores 100. You may still see 110 quoted. That was the bar against an older reference tire that is no longer made, and NHTSA set the new number so the requirement stays about as strict as before.

Three points are worth keeping in mind:

• It’s pass or fail. The symbol shows a tire cleared a minimum bar. It is not a grade, and two tires with the snowflake can perform quite differently.
• It focuses on packed snow. The test looks at traction while accelerating. Braking, cornering and grip on ice are not part of it.
• The mark lasts, the tread doesn’t. The symbol stays on the sidewall for the life of the tire. As the tread wears down, snow grip fades even though the mark is still there.

What about the ice grip symbol?

Some winter tires carry a third, less common mark: the ice grip symbol. It comes from a separate ISO braking test on ice. According to Nokian, a tire must perform at least 18% better than a standard reference tire in that ice braking test to earn it. You won’t see it on every winter tire, so its absence alone doesn’t prove a tire is weak on ice. If ice is your main worry, it is one more clue to look for.

M+S vs. 3PMSF at a glance

Which tires carry which marks

• Dedicated winter tires. These generally carry both 3PMSF and M+S. They combine the tested snow traction with rubber made to stay flexible in the cold and treads full of small slits called sipes. Brands such as Bridgestone, Continental, Nokian, Goodyear and Mastercraft all make winter lines, and you can browse them in our winter tires category.
• All-weather tires. These are meant to stay on the car all year, and they carry the 3PMSF symbol. They suit drivers who see real snow but would rather not swap tires twice a year. They are a compromise, though, not a tire built only for winter.
• All-season tires. Most carry M+S only. Some newer tires sold under an all-season name also have the snowflake, and brands label their lines differently. That is why the sidewall matters more than the name when you shop all-season tires.
• All-terrain tires. Their open tread usually earns M+S. Some models also pass the 3PMSF test, which can make them a reasonable middle ground for pickups and SUVs that see gravel in summer and snow in winter. Check the sidewall of any all-terrain tire you are considering.

How to find the marks on a sidewall

1. Work in good light or use a flashlight. The marks are molded in the same color as the rubber and can be small.
2. Scan the area around the tire size (for example, 225/65R17). Markings are often grouped nearby, but placement varies by brand, so check the whole sidewall.
3. If you can’t find a mark on the outer side, check the inner side too.
4. For 3PMSF, look for the full symbol: three peaks with a snowflake inside. A winter-sounding model name is not the same thing.
5. For M+S, look for the letters M+S, M/S or a close variation.

Shopping online? A product title or category tells you what kind of tire it is, but it may not list every sidewall marking. If a listing doesn’t mention 3PMSF, check the tire maker’s own page for that model and size, or contact us before you order.

What the marks mean for your winter plans

Treat these marks as a starting point, not the whole story.

• Regular snow, cold mornings or icy stretches. Start with tires that carry 3PMSF. If ice and long cold spells are routine, a dedicated winter tire pairs that tested snow traction with cold-weather rubber. Our guide on how to choose the right winter tire walks through vehicle type, size and road conditions.
• Mixed use and moderate winters. A 3PMSF all-weather or all-terrain tire can cover both seasons without a changeover.
• Traction laws. Some states build these marks into their winter rules. Colorado’s Traction Law, for example, accepts AWD or 4WD vehicles on tires marked M+S or M/S, tires with the mountain-snowflake icon, or all-weather rated tires, each with at least 3/16 inch of tread. Vehicles that don’t meet that standard need chains or an approved alternative traction device. Colorado’s own tire guidance also notes that M+S tires are more limited than winter tires, so being legal and being well equipped are not always the same. Rules differ by state and can change, so check the state DOT before a mountain trip.
• Buy a full set. Tire makers advise putting winter tires on all four wheels, whatever your drivetrain, so grip stays balanced front to rear.
• Match your vehicle. Confirm size, load index and speed rating against the door-jamb placard or owner’s manual, and ask a certified tire shop if you’re unsure.

When you order, you can have tires shipped straight to a local installer. Enter the shop’s address as the shipping address and the shop’s name in the Company name field, and call the shop first so they know the tires are coming. Shipping is free on orders to the contiguous US (the 48 states plus Washington, DC), and tracking is emailed when your order ships.