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Snow tires, also known as winter tires, are
tire A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface over which t ...
s designed for use on
snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
and
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
. Snow tires have a tread design with larger gaps than those on conventional tires, increasing traction on snow and ice. Such tires that have passed a specific winter traction performance test are entitled to display a 3PMSF (Three-Peak Mountain Snow Flake) symbol on their sidewalls. Tires designed for winter conditions are optimized to drive at temperatures below . Some snow tires have metal or ceramic studs that protrude from the tire to increase traction on hard-packed snow or ice. Studs abrade dry pavement, causing dust and creating wear in the wheel path. Regulations that require the use of snow tires or permit the use of studs vary by country in Asia and Europe, and by state or province in North America. All-season tires have tread gaps that are smaller than snow tires and larger than conventional tires. They are quieter than winter tires on clear roads, but less capable on snow or ice.


Roadway conditions in winter

Snow tires operate on a variety of surfaces, including pavement (wet or dry), mud, ice, or snow. The tread design of snow tires is adapted primarily to allow penetration of the snow into the tread, where it compacts and provides resistance against slippage. The snow strength developed by compaction depends on the properties of the snow, which depend on its temperature and water content—wetter, warmer snow compacts better than dry, colder snow up to a point where the snow is so wet that it lubricates the tire-road interface. New and powder snow have densities of . Compacted snow may have densities of . Snow or ice-covered roadways present lower braking and cornering friction, compared to dry conditions. The roadway friction properties of snow, in particular, are a function of temperature. At temperatures below , snow crystals are harder and generate more friction as a tire passes over them than at warmer conditions with snow or ice on the road surface. However, as temperatures rise above , the presence of free water increasingly lubricates the snow or ice and diminishes tire friction. Hydrophilic rubber compounds help create friction in the presence of water or ice.
;Dry and moist snow conditions on roadways
File:Mercedes-Benz S203 Yyteri.JPG, Vehicle in cold, dry, powder snow, which offers comparatively better traction than moist snow. File:Саратов пробка у Детского парка.jpg, Vehicles in warm, moist, granular snow encounter decreased roadway traction.


Treads

Attributes that can distinguish snow tires from "all-season" and summer tires include: *An open, deep tread, with a high void ratio between rubber and spaces between the solid rubber *Shoulder blocks, a specialized tread design at the outside of the tire tread to increase snow contact and friction *A narrower aspect ratio between the diameter of the tire and the tread width to minimize resistance from the plowing effect of the tire through deeper snow *
Hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are no ...
rubber compounds that improve friction on wet surfaces *Additional siping, or thin slits in the rubber, that provide more biting edges and improve traction on wet or icy surfaces. Wet-film conditions on hard-compacted snow or ice require studs or chains.


Studs

Many jurisdictions in Asia, Europe, and North America seasonally allow snow tires with metal or ceramic studs to improve grip on packed snow or ice. Such tires are prohibited in other jurisdictions or during warmer months because of the damage they may cause to road surfaces. The metal studs are fabricated by encapsulating a hard pin in a softer material base, sometimes called the ''jacket''. The pin is often made of
tungsten carbide Tungsten carbide ( chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed int ...
, a very hard high performance ceramic. The softer base is the part that anchors the stud in the rubber of the tire. As the tire wears with use, the softer base wears so that its surface is at about the same level as the rubber, whereas the hard pin wears so that it continues to protrude from the tire. The pin should protrude at least for the tire to function properly. Snow tires do not eliminate skidding on ice and snow, but they greatly reduce risks. Studdable tires are manufactured with molded holes on the rubber tire tread. Usually, there are 80 to 100 molded holes per tire for stud insertion. The insertion is done by using a special tool that spreads the rubber hole so that a stud jacket can be inserted and the
flange A flange is a protruded ridge, lip or rim, either external or internal, that serves to increase strength (as the flange of an iron beam such as an I-beam or a T-beam); for easy attachment/transfer of contact force with another object (as the fl ...
at the bottom of the jacket can be fitted nicely to the bottom of the hole. The metal studs come in specific heights to match the depths of the holes molded into the tire tread based on the tread depths. For this reason, stud metals can only be inserted when the tires have not been driven on. A proper stud insertion results in the metal jacket that is flush with the surface of the tire tread having only the pin part that protrudes. When studs come into contact with pavements they abrade the asphalt or concrete surface. This can result in creating polluting dust and wear in the wheel path that prevents proper drainage. For this reason, studded tires are banned, at least seasonally, in many jurisdictions.


Tire/snow interactions

The compacted snow develops strength against slippage along a shear plane parallel to the contact area of the tire on the ground. At the same time, the bottom of the tire treads compress the snow on which they are bearing, also creating friction. The process of compacting snow within the treads requires it to be expelled in time for the tread to compact snow anew on the next rotation. The compaction/contact process works both in the direction of travel for propulsion and braking, but also laterally for cornering. The deeper the snow that the tire rolls through, the higher the resistance encountered by the tire, as it compacts the snow it encounters and plows some of it to either side. At some point on a given angle of uphill pitch, this resistance becomes greater than the resistance to slippage achieved by the tread's contact with the snow and the tires with power begin to slip and spin. Deeper snow means that climbing a hill without spinning the powered wheels becomes more difficult. However, the plowing/compaction effect aids in braking to the extent that it creates rolling resistance.
;Tire/snow interactions
File:Snow tire compacting snow ahead of it.jpg, Compaction of snow under an advancing snow tire, causing rolling resistance while passing through about of snow. File:Impression left by snow tire rolling through snow.jpg, Compaction in about of snow left behind a snow tire, showing tread-snow interaction.


Regulations

ASTM International ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
(American Society for Testing and Materials International) is an international
standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization (SSO) is an organization whose primary function is developing, coordinating, promulgating, revising, amending, reissuing, interpr ...
that develops and publishes voluntary consensus technical
standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object ...
s for a wide range of materials, products, systems, and
services Service may refer to: Activities * Administrative service, a required part of the workload of university faculty * Civil service, the body of employees of a government * Community service, volunteer service for the benefit of a community or a p ...
. The pertinent standard for snow tires is ASTM F1805 – 16, ''Standard Test Method for Single Wheel Driving Traction in a Straight Line on Snow- and Ice-Covered Surfaces'', which assess tire performance on snow and ice. It measures the traction of tires under acceleration in the rolling direction. Tires that pass this test are entitled to display the 3PMSF (Three-Peak Mountain Snow Flake) symbol.


Asia

All
prefectures of Japan Japan is divided into 47 prefectures (, ''todōfuken'', ), which rank immediately below the national government and form the country's first level of jurisdiction and administrative division. They include 43 prefectures proper (, '' ken''), two ...
, except for the southernmost prefecture of
Okinawa is a Prefectures of Japan, prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 Square kilometre, km2 (880 sq mi). ...
, require the motorized vehicles to be fitted with winter tires or tire chains if the road is icy or slushy. If tread grooves of snow tires are worn off for more than 50% of its original depth, tires must be replaced to meet the legal requirements. Drivers will be fined for failing to comply with the snow tire or tire chains requirements. Nationwide studded tire restrictions for passenger vehicles came in effect in April 1991, followed by restrictions for commercial trucks in 1993. Studded tires are technically still legal in Japan, but the usage is restricted by environmental law and it is a criminal offence to operate a vehicle fitted with studded tire on dry asphalt or concrete.


Europe

As of 2016, regulations pertaining to snow tires in Europe varied by country. The principal aspects of regulations were whether use was mandatory and whether studded tires were permitted. *''Mandatory use'' – The following countries required snow tires between specified dates or when roads are snowy or icy: Austria, Bosnia-Herzegovina, Croatia, Czechia, Estonia, Finland, Germany, Latvia, Lithuania, Montenegro, Norway, Romania, Serbia, Slovakia, Slovenia, Sweden, and Russia. *''Studded tires banned'' – The following countries ban the use of studded tires: Albania, Belgium, Bosnia-Herzegovina, Bulgaria, Croatia, Czechia, Germany, Hungary, Luxembourg, North Macedonia, Montenegro, Netherlands, Poland, Portugal, Romania, Serbia, Slovakia, and Slovenia. *''Studded tires restricted'' – The following allowed the seasonally restricted use of studded tires: Austria, Denmark, Estonia, Finland, France, Great Britain, Iceland, Ireland, Latvia, Lithuania, Norway, Russia, Spain, Sweden, and Switzerland.


North America

The U.S.
National Highway Traffic Safety Administration The National Highway Traffic Safety Administration (NHTSA ) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" rela ...
(NHTSA) and
Transport Canada Transport Canada (french: Transports Canada) is the department within the Government of Canada responsible for developing regulations, policies and services of road, rail, marine and air transportation in Canada. It is part of the Transporta ...
allow display of a ''3PMSF'' symbol to indicate that the tire has exceeded the industry requirement from a reference (non-snow) tire. As of 2016, snow tires were 3.6% of the US market and 35% of the Canadian market. US states and Canadian provinces control the use of snow tires. Quebec is the only state or province that requires snow tires jurisdiction-wide. They may require snow tires or chains only in certain areas during the winter: *'' British Columbia'' – Snow tires are only required by law in certain "designated winter tire & chain-up routes" in mountainous regions. In these areas, motorists must use winter tires or carry tire chains. *''
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Terri ...
'' –
Banff National Park Banff National Park is Canada's oldest national park, established in 1885 as Rocky Mountains Park. Located in Alberta's Rocky Mountains, west of Calgary, Banff encompasses of mountainous terrain, with many glaciers and ice fields, dense conif ...
or
Jasper National Park Jasper National Park is a national park in Alberta, Canada. It is the largest national park within Alberta's Rocky Mountains spanning . It was established as a national park in 1930 and declared a UNESCO World Heritage Site in 1984. Its locatio ...
require cars to have snow tires or tire chains between 1 November to 31 March, or any other period during which the road is covered with snow or ice. *''
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirteen ...
'' – Winter tires or studded tires must be used from 1 December to 15 March. The use of studded tires is regulated in the United States and Canada by individual states and provinces, as follows: *Unrestricted use of studded snow tires is allowed in: (United States'')'' Colorado, Kentucky, North Carolina, Vermont, and Wyoming; (Canada'')'' Alberta, Northwest Territories, Saskatchewan, and Yukon **South Carolina – only restriction is studs must be no more than 1/16 of an inch. **Wyoming – chains must be used during snow emergencies. *Studded snow tires may not be used in Hawaii, Mississippi, Puerto Rico, or Southern Ontario. **Georgia – only during "snow and ice" conditions. **Illinois – prohibited for nearly all vehicles; only rural mail carriers and persons with disabilities in rural areas may use, 15 November – 1 April. **Minnesota – rural mail carriers and non-residents (maximum of 30 days) only, 1 November – 15 April; The non-resident exemption does not extend to out-of-state students and non-residents employed in Minnesota. **Wisconsin – only mail carriers, school buses and emergency vehicles, 15 November – 1 April; vehicles registered in states which permit studded tires may use in Wisconsin for up to 30 days during the same window. *All other states and provinces allow seasonal use of studded snow tires. **Alabama, Alaska, Florida, Louisiana, Michigan and Texas – only rubber studs are allowed. **Alaska – 16 September – 30 April north of 60 degrees north latitude (including
Anchorage Anchorage () is the largest city in the U.S. state of Alaska by population. With a population of 291,247 in 2020, it contains nearly 40% of the state's population. The Anchorage metropolitan area, which includes Anchorage and the neighboring Ma ...
and
Fairbanks Fairbanks is a home rule city and the borough seat of the Fairbanks North Star Borough in the U.S. state of Alaska. Fairbanks is the largest city in the Interior region of Alaska and the second largest in the state. The 2020 Census put the p ...
); 1 October – 14 April south of 60 degrees north latitude (including
Juneau The City and Borough of Juneau, more commonly known simply as Juneau ( ; tli, Dzánti K'ihéeni ), is the capital city of the state of Alaska. Located in the Gastineau Channel and the Alaskan panhandle, it is a unified municipality and the ...
). **Idaho – firefighting vehicles may use year-round; all other vehicles may use 1 October – 30 April. **New Brunswick - Vehicles may use between 15 October - 1 May. **Newfoundland & Labrador - Vehicles may use 1 November - 30 April. **North Dakota – school buses may use year-round; all other vehicles may use 15 October – 15 April. **Nova Scotia - Fire department vehicles may use year-round; all other vehicles may use 15 October - 31 May. **Prince Edward Island - All vehicles may use between 1 October - 31 May. **South Dakota – school buses and municipal fire vehicles may use year-round; all other vehicles may use 1 October – 30 April.


See also

*
Snow chains Snow chains, or tire chains, are devices fitted to the tires of vehicles to provide increased traction when driving through snow and ice. Snow chains attach to the drive wheels of a vehicle or special systems deploy chains which swing under ...
*
Snow socks Snow socks (also known as auto socks) are textile alternatives to snow chains. Snow sock devices wrap around the tires of a vehicle to increase traction on snow and ice. Snow socks are normally composed of a woven fabric with an elastomer attach ...


References

{{DEFAULTSORT:Snow Tires Tires Snow Ice in transportation Inclement weather management Automotive safety Vehicle safety technologies
Tyres A tire (American English) or tyre (British English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineering), t ...