Snow tire

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 . ;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. 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. ;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. Tread Attributes that can distinguish snow tires from "all-season" and summer tires include the following: 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, 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. Studded 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 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, metal studs can be inserted only 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. ==Standards==

Regardless of what conditions a tire is designed to handle, regional authorities may require minimum tread depth such as 6/32 or 3/16-inch (~4.75mm) in the U.S. or 4mm (~5/32in) in Europe, the use of chains, or close road access all together in freezing conditions. Snow: M+S The M+S tire code arose in the 1970s to indicate tires whose tread design performs better in "Mud and Snow" conditions than regular "non-M+S" street tires, and is distinct from the tire code "M+T" for "Mud and Terrain". The USTMA includes requirements that M+S tire tread has recesses that extend at least 1/2 inch from the edge toward the center, with a minimal cross-section of 1/16 inch, and be angled to the direction of travel from 35 to 90 degrees (perpendicular). The Tire and Rubber Association of Canada (TRAC, formerly the Rubber Association of Canada) also uses USTMA standards. The ISO defines both "snow tyre" and "mud and snow tyre" (UN R117) definitions and revisions have used M+S to indicate tires whose tread pattern, tread compound or structure are designed to outperform a normal tire in "mud and fresh or melting snow". Whether a tire has a "M+S marking (Y/N)" is included "grip index" test report forms. Reg. No. 172. Currently, 68 countries have signed to UN Regulations regarding tires, the United States and Canada being the two notable exceptions which use USTMA and their respective laws. Severe Snow: Alpine Symbol, 3PMSF The Alpine Symbol or Three-Peak Mountain Snow Flake (3PMSF) pictogram depicts a "mountain profile" with "three peaks with the middle peak being the tallest" containing "a six-sided snowflake" half the height of the tallest peak is an international indicator of tires of various classes rated for "severe snow use", such as a passenger vehicle tire that performs 10 to 12% better in straight-line "traction test" than a Standard Reference Test Tire (SRTT) to meet USTMA's standard . It is used in addition and adjacent to the M+S mark, and was standardized in 1999. Snow tires should be installed on all wheels, never just the front which could lead to adverse handling. ISO defines a "severe snow use tyre". The USTMA requires of tires for "severe snow conditions" equal or exceed that of a SRTT using straight line "traction test" ASTM F1805-18 on a medium packed snow surface. For example, with the SRTT having a SG of 1.00, a 14-inch tire would need a SG of 1.10, and a 16-inch tire a SG of 1.12, basically 10 or 12% better respectively. UN R117 requires "severe snow" tires for a passenger car (C1) to equal or exceed a "brake test" SG of 1.07 and "traction test" SG of 1.10, while light commercial (C2) have a lesser "brake test" SG of 1.02, whereas heavy duty (C3) vehicles only "acceleration test" SG of 1.25. Whether a tire has a "3PMSF marking (Y/N)" is also included grip index test report forms. It is placed in addition and adjacent to both the 3PMSF mark (whose requirements it must also meet) and M+S mark, and was standardized in 2021. Tires for "ice conditions" should be installed on all wheels, never just the front which could lead to adverse handling. UN R117 defines an "ice grip tyre" as 3PMSF-rated passenger car tire with a GI of 1.18 or greater using the same procedures used by USTMA. Studded tires should be installed on all wheels, never just the front which could lead to adverse handling. Whether to avoid rear-end collisions or damage from flung material, some countries have used the same Ш "Sha" in a red triangle on the rear of studded vehicles to alert following motorists (Russian law 1993-2018, Ukraine present), a similar logo (Lithuania), or a spiked tire logo (Austria). ==Regulations==

Asia All prefectures of Japan, except for the southernmost prefecture of Okinawa, have a traffic regulation requiring motorized vehicles to be fitted with winter tires or tire chains when the road is covered by ice or snow. In addition, tire chains must be fitted for all vehicles on rural designated highways in snow country regions when regulated by traffic signs requiring tire chains. In many prefectures, tread grooves of snow tires are worn off for more than 50% of their original depth, tires must be replaced to meet the legal requirements. Studded tires are still legal in Japan, but their usage is restricted by environmental law and it is a criminal offence to operate a vehicle fitted with a studded tire on dry asphalt or concrete. • Snow tires mandatory between specified dates or when roads are snowy or icy: Austria, Bosnia-Herzegovina, Croatia, Czechia, Estonia, Finland, France, Germany, Latvia, Lithuania, Montenegro, Norway, Romania, Serbia, Slovakia, Slovenia, Sweden, and Russia. • Studded tires restricted seasonally: Austria, Denmark, Estonia, Finland, France, Iceland, Ireland, Latvia, Lithuania, Norway, Russia, Spain, Sweden, and Switzerland. • Studded tires banned: Albania, Belgium, Bosnia-Herzegovina, Bulgaria, Croatia, Czechia, Germany, Hungary, Luxembourg, North Macedonia, Montenegro, Netherlands, Poland, Portugal, Romania, Serbia, Slovakia, and Slovenia. North America NHTSA (United States) and Transport Canada allow the 3PMSF symbol on tires that meet or exceed 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. Canada : sign seasonally requiring 3PMSF or M+S tires.The U.S. National Highway Traffic Safety Administration Federally, Transport Canada advises drivers to use winter tires on snow- or ice-covered roads. Canada’s provinces, territories, and national parks also have various winter-tire and traction requirements, which differ by date, location, weather conditions, and vehicle classification. Quebec is the only jurisdiction that requires vehicles registered therein to have 3PMSF-rated or studded tires December 1 through March 15 regardless of weather. United States : Some U.S. states, especially those in snowy or mountainous regions ==See also==