Winter tires: when to switch and what to buy

Jump to: When to switch · 3PMSF vs M+S · All season vs all weather vs winter · Studded tires · Tread depth for snow · Fit four · Cold weather pressure · Swap checklist

When to switch: the 45°F (7°C) rule

Temperature matters more than the calendar or the first snowfall. Transport Canada explains that below 7°C (about 45°F) all season and summer tires begin to lose elasticity, which means less traction, while winter tires keep their elasticity and grip at much lower temperatures. The Tire and Rubber Association of Canada gives the same trigger: change over once the temperature consistently stays below 7°C.

• Fall: book the swap when daytime highs start sitting near 45°F. Cold, dry pavement is part of the reason, not only snow.
• Spring: swap back once temperatures stay above that point. Soft winter compounds are designed for the cold, so follow your tire maker’s guidance on warm weather use.
• Plan ahead: shops often get busy after the first storm, so an early appointment is easier than a last minute one.

Reading the sidewall: 3PMSF vs M+S

Two markings cause most of the confusion. They are not the same thing.

Marking	What it means	What it does not tell you
M+S (also M/S, M&S, MS)	Meets the USTMA “snow tire” definition. Common on all season tires.	It is not a snow traction test result. CAA says tires marked only M and S are not winter tires.
3PMSF (three peak mountain with a snowflake)	The tire reached a minimum snow grip index against a standard reference tire in a packed snow traction test (USTMA TISB 37). USTMA places it next to the M+S marking.	The test is on medium packed snow, so it does not rate ice grip, wear, or dry braking.

Deciding between one set of all weather tires and all seasons? See our all weather vs all season tires comparison, with a climate picker and Quebec and BC rules.

USTMA describes tires that qualify for the mountain snowflake as having superior snow performance compared with tires that only meet its basic M+S snow tire definition. When you shop, look for the symbol on the sidewall of the exact size you buy, since markings can vary by size within one model line.

All season vs all weather vs winter

Type	Typical markings	Best fit	Trade off
All season	Usually M+S, often no 3PMSF	Mild winters with rare snow, one set all year	Loses grip as temperatures fall below about 45°F
All weather	M+S plus 3PMSF	Changeable winters with some snow, drivers who want one set	A compromise; not built around ice and deep cold like a dedicated winter tire
Winter (studless or studdable)	3PMSF, often M+S too	Regular ice, packed snow, long stretches below freezing	Needs a second set, seasonal swaps, and storage

The Government of British Columbia notes that 3PMSF tires, which include all weather tires, offer better traction on snow and ice, and recommends them for cold weather driving. For a wider look at trade offs, see all season vs winter and all season vs winter vs summer.

Studded tires: check your state first

Studded tire rules are set by each state, and they differ. Some states allow studs only between set dates, and some restrict them further. Washington is a clear example: studded tires are legal there only from November 1 to March 31, the dates apply to visitors too, and there are no individual or out of state waivers. WSDOT also notes that Washington and Oregon share the March 31 removal date while other states may follow different timelines.

• Look up the rules on your state DOT or DMV website, and on the sites of any state you will drive through.
• Studless winter tires with the 3PMSF symbol are an option where studs are restricted.
• Studs are not the same as chains. In Washington, studded tires do not satisfy a posted chain requirement.

Tread depth for snow

Snow grip depends on tread depth, so a winter tire that is legal for summer roads may already be weak in snow. As one government benchmark, British Columbia requires at least 3.5 mm of tread (about 4/32 inch) for a tire to count as a legal winter tire on its posted routes. Check depth across the full width of each tire before the season starts, and see our tread depth guide for how to measure. Also read the DOT date code, because a stored set ages even when the tread looks fine.

Fit four winter tires, not two

Transport Canada advises installing winter tires in sets of four, ideally with the same type, size, speed rating, and load index on every wheel, and not mixing tread patterns or construction. The Tire and Rubber Association of Canada warns never to fit winter tires on the front axle only, because the extra front grip can make the rear slide out (oversteer).

Before you buy, copy the size, load index, and speed rating from your door placard and confirm the winter tire you choose with your installer. See load index and speed rating for how to read the service description.

Cold weather tire pressure

Tire pressure falls as the air gets colder, so the first cold snap often brings a TPMS warning light. Check cold pressure with a gauge at least monthly, and again after a big temperature drop, and set it to the door placard cold PSI, not the maximum on the sidewall. Expect roughly 1 to 2 psi less for every 10°F drop; the cold weather PSI drop calculator gives a quick range.

Seasonal swap checklist

1. Watch the forecast. Book the swap when highs settle around 45°F (7°C).
2. Inspect the winter set for tread depth, cracks, bulges, and age before mounting.
3. Fit all four, matched in size, type, load index, and speed rating as your installer advises.
4. Ask about TPMS sensors if the winter set is on its own wheels.
5. Set cold pressure to the placard value after mounting, and recheck after the first cold week.
6. Clean and store the off season set properly. See our seasonal tire storage guide.

Informational only, not professional, safety, or legal advice. Local laws and your vehicle’s documents take priority, and a licensed installer should mount and balance your tires.